BTB-BACK-TAZ domain protein MdBT2-mediated MdMYB73 ubiquitination negatively regulates malate accumulation and vacuolar acidification in apple

As an important primary metabolite,malate plays a key role in regulating osmotic pressure,pH homeostasis,stress tolerance,and fruit quality of apple.The R2R3-MYB transcription factor(TF)MdMYB73 was identified as a protein that plays a critical role in determining malate accumulation and vacuolar acidification by directly regulating the transcription of aluminum-activated malate transporter 9(MdALMT9),vacuolar ATPase subunit A(MdVHA-A),and vacuolar pyrophosphatase 1(MdVHP1)in apple.In addition,the bHLH TF MdCIbHLH1 interacts with MdMYB73 and enhances the transcriptional activity of MdMYB73.Our previous studies demonstrated that the BTB-BACK-TAZ domain protein MdBT2 can degrade MdCIbHLH1 to influence malate accumulation and vacuolar acidification.However,the potential upstream regulators of MdMYB73 are currently unknown.In this study,we found that MdBT2 directly interacts with and degrades MdMYB73 through the ubiquitin/26S proteasome pathway to regulate malate accumulation and vacuolar acidification.A series of functional assays with apple calli and fruit showed that MdBT2 controls malate accumulation and vacuolar acidification in an MdMYB73-dependent manner.Overall,our findings shed light on the mechanism by which the BTB-BACK-TAZ domain protein MdBT2 regulates malate accumulation and vacuolar acidification by targeting MdMYB73 and MdCIbHLH1 for ubiquitination in apple.This information may help guide traditional breeding programs and fruit tree molecular breeding,and lead to improvements in fruit quality and stress tolerance.

Malate and Lactate Dehydrogenases of a Freshwater Catfish: Impact of Endosulfan

A sublethal concentration of technical grade endosulfan (END) inhibited 35 to 55% of the activities of cytoplasmic malate dehydrogenase (cMDH), mitochondrial malate dehydrogenase (mMDH), and lactate dehydrogenase (LDH) in the liver and the skeletal muscle of a freshwater catfish, Clarias halrachus, after 7 days of exposure. The activity remained in the inhibited state up to 28 days. The withdrawal of END from the medium after 1 week of exposure gradually restored the activities to control levels within 21 days in the skeletal muscle and 28 days in the liver. The administration of actinomycin D or cycloheximide between the 14th and the 21st day of the withdrawal of END almost completely inhibited the withdrawal-dependent recovery in the activities of all the three enzymes. This indicates de novo synthesis of the enzymes during the recovery period. A conjoint treatment of END and triiodothyronine (T_3) raised the activities of cMDH, mMDH, and LDH in the liver and the skeletal muscle up to the control levels. This shows that the inhibitory effect of END may be relieved in presence of T_3. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed few changes in the pattern of cytoplasmic proteins of the liver and the skeletal muscle in response to exposure to END. 1990 Academic Press. Inc.

Effect of Nitric Oxide on the Interaction Between Mitochondrial Malate Dehydrogenase and Citrate Synthase

Mitochondrial malate dehydrogenase （mMDH） and citrate synthase （CS） are sequential enzymes in Krebs cycle. mMDH, CS and the complex between mMDH and CS （mMDH＋CS） were treated with nitric oxide solution. The roles of notric oxide （NO） on the secondary structures and the interactions between mMDH and CS were studied using circular diehroism （CD） and Fourier transform surface plasmon resonance （FT-SPR）, respectivley. The effects of NO on the activities of mMDH, CS and mMDH＋CS were also studied. And the regulations by NO on mMDH and CS were simulated by PyMOL software. The results of SPR conifrmed that strong interaction between mMDH and CS existed and NO could signiifcantly regulate the interaction between the two enzymes. NO reduced the mass percents ofα-helix and increased that of random in mMDH, CS and mMDH＋CS. NO increased the activities of CS and mMDH＋CS, and inhibited the activity of mMDH. Graphic simulation indicated that covalent bond was formed between NO and Asn242 in active site of CS. However, there was no direct bond between NO and mMDH. The increase in activity of mMDH＋CS complex depended mostly on the interaction between NO and CS. All the results suggested that the regulations by NO on the activity and interaction between mMDH and CS were accord with the changes in mMDH, CS and mMDH＋CS caused by NO.

Solid and Solution Structural Studies of Dimeric and Tetrameric Molybdenum(VI) Malate Complexes

Reactions of potassium molybdate with racemic malic acid （H3mal = C4H6O5） result in the isolation of two mesomeric molybdenum malate complexes K8[（MoO2）2O（R-mal）2][（MoO2）2O（Smal）2]-4H2O 1 and （Him）2K6[（MoO2）4O3（R-mal）2][（MoOE）4O3（S-mal）2]-8H2O 2. Complex 1 belongs to the monoclinic system, space group C2/c with a = 14.8637（3）, b = 6.9544（1）, c = 19.6783（5）A, β = 100.081（2）°, V = 2002.70（7） A^3, Mr = 1452.88, Z = 2, F（000） = 1416, T = 173 K, Dc = 2.409 g/cm3, fl（MoKa＇） = 2.167, R = 0.0283 and wR = 0.0733.2 is of triclinic system, space group P1^- with a = 8.7707（2）, b = 9.3310（3）, c = 17.9093（7）A, α= 83.781（3）, β = 85.626（2）, y= 84.822（2）°, V = 1447.84（8）A^3, Mr = 2160.68, Z = 1, F（000） = 1048, T = 173 K, Dc = 2.478 g/cm^3,μ（MoKα） = 2.230, R = 0.0234 and wR = 0.0584.1 is the first isolated dinuclear molybdenum（VI） malato complex in 1：1 molar ratio. The molybdenum atoms in the two complexes are six-coordinated in an approximately octahedral geometry. Two malates coordinate tridentately with the Mo atom via their α-alkoxy, α-carboxy and α-carboxy groups in 1 and 2. β-Carboxy group in 2 further links with the other two Mo atoms to give a tetrameric unit. The solution ^1H and ^13C NMR spectra indicate that dimeric malate molybdenum in 1 dissociates partly in solution and exists in an equilibrium with tetrameric species, while 2 is stable and retains its tetrameric structure without any dissociation.

Molecular Weight of Cytoplasmic Malate Dehydrogenase,Mitochondrial Malate Dehydrogenase and Lactate Dehydrogenase of a Freshwater Catfish

The multiple molecular forms of cytoplasmic malate dehydrogenase (cMDH), mitochondrial malate dehydrogenase (mMDH ) and lactate dehydrogenase (LDH ) were studied in the liver and skeletal muscle of the freshwater catfish, Clarias batrachus. There were two electrophoretically distinguishable bands (AA andBB) of cMDH and mMDH which suggests that they are apparently encoded at two gene loci (A and B) in both the tissues.However, the presence of a single band (LDH-1 ) of LDH in liver and double bands (LDH-1and LDH-2) in skeletal muscle in which LDH-2 was predominant reflects the differential expression of LDH genes in different metabolic tissues to meet the requirement of energy production. The AA isoform (74 kd) of liver cMDH was smaller than those of the AA form (110 kd) of skeletal muscle. In contrast, the BB isoform of liver (42 kd) and skeletal muscle (54 kd) were more or less similar in size. Unlike the case of cMDH, the molecular weight of AA isoform (115 kd) of liver mMDH was higher than those of the AA form (87kd) of skeletal muscle. Whereas the molecular weight of BB isoform (58 kd) of liver was in proximity to the weight of BB form (44 kd) of skeletal muscle mMDH. The size of AA isoform (74 kd) of liver cMDH was smaller, while the AA isoform (110 kd) of skeletal muscle was larger as compared to AA form of mMDH in the liver (115 kd) and skeletal muscle (87 kd). But the size of BB isoform of both the isozymes was almost equal in these metabolic tissues. The molecular weight of liver LDH-1 (96 kd) was close to the weight of LDH-1 (82 kd) in skeletal muscle. The molecular weight of skeletal muscle LDH-2 was deduced as 37 kd which is much more lower than the weight of LDH-1 in liver and skeletal muscle. The smaller size of LDH-2 in skeletal muscle may be of a physiological significance in this anaerobic tissue

Duplication of Locus Coding of Malate Dehydrogenase in Populus tomentosa Carr

Horizontal starch-gel electrophoresis was used to study crude enzyme extraction from young leaves of 234 clones of Populus tomentosa Cart. selected from nine provenances in North China. Ten enzyme systems were resolved. One hundred and fifty-six clones showing unusual allozyme band patterns at locus Mdh-Ⅰ were found. Three allozyme bands at locus Mdh-Ⅰ were 9：6：1 in concentration. Further studies on the electrophoretic patterns of ground mixed pollen extraction of 30 male clones selected at random from the 156 clones were conducted and it was found that allozyme bands at locus Mdh-Ⅰ were composed of two dark-stained bands and a weak band. Only one group of the malate dehydrogenase （MDH） zymogram composed of two bands was obtained from the electrophoretic segregation of pollen leachate of the same clones. A comparison of the electrophoretic patterns one another suggested that the locus Mdh-Ⅰ coding malate dehydrogenase in diploid species of P. tomentosa was duplicated. The duplicate gene locus possessed three same alleles and was located in mitochondria. The locus duplication of alleles coding malate dehydrogenase in P.tomentosa was discovered and reported for the first time.

Different Effects of Malate on the Activities of Photosystem II in Detached Leaves of Maize and Tobacco

Malate is the first stable product after CO2 is fixed in NADP-dependent malic enzyme (NADP-ME) type of C4 plants, which transfers CO2 and the reducing equivalent from mesophyll cell (MC) to vascular bundle sheath cell (BSC) chloroplasts and affects the redox state of BSC. The aim of this experiment is to investigate the effect of exogenous malate on the activity of photosystem II (PS II) in C4 and C3 plants. The leaf discs from the 5th fully expanded leaves of maize (NADP-ME type C4 plants) and the 10th fully expanded leaves of tobacco (C3 plants) were treated with malate of 50, 100 μM and the chlorophyll fluorescence parameters were measured. Malate treatments decreased the photochemical reaction efficiency (FV/FM) in maize leaves, as a result of rising in initial fluorescence (FO) and decreasing in maximal fluorescence (FM). The number of active PS II reaction center (RC) per excited cross section (RC/CS) declined in malate-treated maize, suggesting that malate inactivated PS II RC. Malate treatments also increased Wk, representing the severity of oxygen-evolving complex (OEC) damage, and decreased the rate of photosynthetic oxygen evolution. We conclude that exogenous malate regulates the activity and structure of PS II in C4 plant maize. No significant changes in the activity of PS II were observed in malate-treated C3 plant tobacco. It is suggested that the short term malate treatment will inhibit PS II of leaves which have C4 anatomy and C4 enzymes.

Structural Basis for the Interaction of 14-3-3<i>β</i>with Tricarboxylic Acid Cycle Intermediate Malate

The protein family of 14-3-3(s) has risen to a position of higher importance as an adaptor protein in cell biology. The seven highly conserved human 14-3-3 proteins coordinate diverse cellular processes including apoptosis, DNA damage response, protein trafficking, and others. In liver hepatocytes, 14-3-3β binds to Ser196-phosphorilated glucose-responsive carbohydrate response element-binding protein (ChREBP) to inhibit converting excess carbohydrate to fat by regulating the nuclear/cytosol trafficking of ChREBP. Here, we report X-ray crystal structures of homodimeric mammalian 14-3-3β in its apo, Malate-bound forms. The determined apo structure was captured with one monomer in the closed state, whereas the other one had an open conformation. Strikingly, 14-3-3β binds Malate dynamically with a double-closed state, which is distinct from all previously characterized 14-3-3(s) and target ligand-binding modes. Malate docks into a first-time observed cofactor pocket located at the concaved interface of 14-3-3β helices α2, α3, α4 through mainly electrostatic and hydrogen interactions. Such a Tricarboxylic Acid Cycle intermediate Malate bond model might offer a new approach to further analyze insulin-independent 14-3-3/ChREBP pathway of de novo fat synthesis in the liver.

A Review on Molecular Physiology of Malate and Lactate Dehydrogenases in Fishes

The malate(EC 1.1.1.37)and lactate(EC 1.1.1.27)dehydrogenases are themetabolic enzymes directly or indirectly involved in energy production,gluconeogenesis and lipogenesis.Malate dehydrogenase(MDH)exists in twoisoenzymic forms,cytoplasmic(cMDH)and mitochondrial(mMDH),composed of Aand/or B subunits(dimeric molecule:MW 40,000-120,000).Lactate dehydrogenase(LDH)has tetrameric(MW 35,000-110,000)structure made up of either A and/or B,orC(C,E,F)subunits.They catalyze an ordered bisubstrate(substrate and coenzyme)

Whole-genome resequencing identifies candidate genes and allelic variation in the MdNADP-ME promoter that regulate fruit malate and fructose contents in apple

Soluble sugar and organic acids are key determinants of fruit organoleptic quality and directly affect the commodity value and economic returns of fruit crops.We performed whole-genome sequencing of the apple varieties Gala and Xiahongrou,along with their F1 hybrids,to construct a high-density bin map.Our quantitative genetic analysis pinpointed 53 quantitative trait loci(QTLs)related to 11 sugar and acid traits.We identified a candidate gene,MdNADP-ME,responsible for malate degradation,in a stable QTL on linkage group 15.Sequence analysis revealed an A/C SNP in the promoter region(MEp-799)that influences binding of the MdMYB2 transcription factor,thereby affecting MdNADP-ME expression.In our study of various apple genotypes,this SNP has been demonstrated to be linked to malate and fructose levels.We also developed a dCAPS marker associated with fruit fructose content.These results substantiate the role of MdNADP-ME in maintaining the equilibrium between sugar and acid contents in apple fruits.

Molecular Characterization of a Cytosolic Malate Dehydrogenase Gene（GhcMDH1） from Cotton

Malate dehydrogenase（MDH） is a key enzyme that catalyzes the reversible oxidation of oxaloacetate to malate and plays an important role in the physiological processes of plant growth and development. However, cyto- solic malate dehydrogenase（cMDH）, which is crucial for malate synthesis in the cytosol, still has not been extensively characterized in plants. Here, we isolated a cytosolic malate dehydrogenase gene, designated as GhcMDH1, from Gossypium hirsutum and characterized its possible molecular function in cotton fiber. The cloned cDNA of GhcMDH1 is 1520 base pairs in length, and has an open reading frame of 999 base pairs, encoding for 332 amino acid residues with an estimated molecular weight of 35580 and pI of 6.35. Sequence alignment showed that the de- duced amino acid sequence of GhcMDH1 protein shared a high similarity to other plant cMDHs. Confocal and im- munological analysis confirmed that GhcMDH1 protein was subcellularly localized to the cytosol. Quantitative real-time polymerase chain reaction（PCR） revealed that GhcMDH1 was constitutively expressed in all vegetative cotton tissues, with slightly lower levels in roots than stems and leaves. Interestingly, the transcripts of GhcMDH1 were detected in 5--25 d post anthesis（DPA） fibers and highly abundant at 15 DPA fibers. The total MDH activities and malate contents of cotton fibers were positively correlated with the fiber elongation rates, suggesting that GhcMDH1 may function in malate synthesis in fast fiber elongation. In agreement with this suspicion, the recombi- nant His-GhcMDH1 protein mainly drives the reaction towards malate generation in vitro. In conclusion, our mole- cular characterization of the GhcMDH1 gene provides valuable insights to further investigate the malate equilibrium in cotton fiber development.

The Plastid-Localized NAD-Dependent Malate Dehydrogenase Is Crucial for Energy Homeostasis in Developing Arabidopsis thaliana Seeds

In the absence of photosynthesis, ATP is imported into chloroplasts and non-green plastids by ATP/ADP transporters or formed during glycolysis, the latter requiring continuous regeneration of NAD＋, supplied by the plastidial isoform of NAD-MDH. During screening for T-DNA insertion mutants in the plNAD-MDH gene of Arabidopsis, only heterozygous plants could be isolated and homozygous knockout mutants grew only after complementation. These heterozygous plants show higher transcript levels of an alternative NAD＋-regenerating enzyme, NADH-GOGAT, and, remarkably, improved growth when ammonium is the sole N-source. In situ hybridization and GUS-histochemical stain- ing revealed that plNAD-MDH was particularly abundant in male and female gametophytes. Knockout plNAD-MDH pollen exhibit impaired tube growth in vitro, which can be overcome by adding the substrates of NADH-GOGAT. In vivo, knockout pollen is able to fertilize the egg cell. Young siliques of selfed heterozygous plants contain both green and white seeds corresponding to wild-type/heterozygous （green） and homozygous knockout mutants （white） in a （1：2）：1 ratio. Embryos of the homozygous knockout seeds only reached the globular stage, did not green, and developed to tiny wrinkled seeds. Complementation with the gene under the native promoter rescued this defect, and all seeds developed as wild-type. This suggests that a blocked major physiological process in plNAD-MDH mutants stops both embryo and endosperm development, thus avoiding assimilate investment in compromised offspring.

Lung protective effects of dietary malate esters derivatives from Bletilla striata against SiO_(2) nanoparticles through activation of Nrf2 pathway

Objective: To study the protective activities of the dietary malate esters derivatives of Bletilla striata against SiO_(2)nanoparticles-induced A549 cell lines and its mechanism action.Methods: The components were isolated and elucidated by spectroscopic methods such as 1D NMR and 2D NMR. And MTT assays was used to tested these components on the A549 cell survival rates and ROS or proteins levels were detected by Western blotting.Results: A new glucosyloxybenzyl 2-isobutylmalate(a malate ester derivative), along with 31 known compounds were isolated and identified from n-BuOH extract of EtOH extract of B. striata. Among them,compounds 3, 4, 11, 12 and 13 possessed noteworthy proliferative effects for damaged cells, with ED50of 14.0, 13.1, 3.7, 11.6 and 11.5 μmol/L, respectively, compared to positive control resveratrol(ED50, 14.7 μmol/L). Militarine(8) prominently inhibited the intracellular ROS level, and increased the expression of Nrf2 and its downstream genes(HO-1 and γ-GCSc). Furthermore, Nrf2 activation mediates the interventional effects of compound 8 against SiO_(2)nanoparticles(nm SiO_(2))-induced lung injury.Moreover, treatment with compound 8 significantly reduced lung inflammation and oxidative stress in nm SiO_(2)-instilled mice. Molecular docking experiment suggested that 8 bound stably to the HO-1 protein by hydrogen bond interactions.Conclusion: The dietary malate esters derivatives of B. striata could significantly increase the viability of nm SiO_(2)-induced A549 cells and decrease the finer particles-induced cell damages. Militarine is especially promising compound for chemoprevention of lung cancer induced by nm SiO_(2)through activation of Nrf2 pathway.

Brassinosteroid signaling regulates phosphate starvation-induced malate secretion in plants

Inorganic phosphate(Pi)is often limited in soils due to precipitation with iron(Fe)and aluminum(Al).To scavenge heterogeneously distributed phosphorus(P)resources,plants have evolved a local Pi signaling pathway that induces malate secretion to solubilize the occluded Fe-P or Al-P oxides.In this study,we show that Pi limitation impaired brassinosteroid signaling and downregulated BRASSINAZOLE-RESISTANT 1(BZR1)expression in Arabidopsis thaliana.Exogenous 2,4-epibrassinolide treatment or constitutive activation of BZR1(in the bzr1-D mutant)significantly reduced primary root growth inhibition under Pi-starvation conditions by downregulating ALUMINUM-ACTIVATED MALATE TRANSPORTER 1(ALMT1)expression and malate secretion.Furthermore,At BZR1 competitively suppressed the activator effect of SENSITIVITY TO PROTON RHIZOTOXICITY 1(STOP1)on ALMT1 expression and malate secretion in Nicotiana benthamiana leaves and Arabidopsis.The ratio of nuclear-localized STOP1 and BZR1 determined ALMT1 expression and malate secretion in Arabidopsis.In addition,BZR1-inhibited malate secretion is conserved in rice(Oryza sativa).Our findings provide insight into plant mechanisms for optimizing the secretion of malate,an important carbon resource,to adapt to Pi-deficiency stress.

Legume-specific SnRK1 promotes malate supply to bacteroids for symbiotic nitrogen fixation

Nodulation is an energy-expensive behavior driven by legumes by providing carbon sources to bacteroids and obtaining nitrogen sources in return.The energy sensor sucrose nonfermenting 1-related protein kinase 1(SnRK1)is the hub of energy regulation in eukaryotes.However,the molecular mechanism by which SnRK1 coordinates the allocation of energy and substances during symbiotic nitrogen fixation(SNF)remains unknown.In this study,we identified the novel legume-specific SnRK1α4,a member of the SnRK1 family that positively regulates SNF.Phenotypic analysis showed that nodule size and nitrogenase activity increased in SnRK1α4-overexpressing plants and decreased significantly in snrk1α4 mutants.We demonstrated that a key upstream kinase involved in nodulation,Does Not Make Infection 2(DMI2),can phosphorylate SnRK1α4 at Thr175 to cause its activation.Further evidence clarified that SnRK1α4 phosphorylates the malate dehydrogenases MDH1/2 to promote malate production in the cytoplasm,supplying carbon sources to bacteroids.Therefore,our findings reveal an essential role of the DMI2–SnRK1α4–MDH pathway in supplying carbon sources to bacteroids for SNF and provide a new module for constructing cereal crops with SNF.

Regulation of a vacuolar proton-pumping P-ATPase MdPH5 by MdMYB73 and its role in malate accumulation and vacuolar acidification

As the main organic acid in fruits,malate is produced in the cytoplasm and is then transported into the vacuole.It accumulates by vacuolar proton pumps,transporters,and channels,affecting the taste and flavor of fruits.Among the three types of proton pumps(V-ATPases,V-PPases,and P-ATPases),the P-ATPases play an important role in the transport of malate into vacuoles.In this study,the transcriptome data,collected at different stages after blooming and during storage,were analyzed and the results demonstrated that the expression of MdPH5,a vacuolar proton-pumping P-ATPase,was associated with both pre-and post-harvest malate contents.Moreover,MdPH5 is localized at the tonoplast and regulates malate accumulation and vacuolar pH.In addition,MdMYB73,an upstream MYB transcription factor of MdPH5,directly binds to its promoter,thereby transcriptionally activating its expression and enhancing its activity.In this way,MdMYB73 can also affect malate accumulation and vacuolar pH.Overall,this study clarifies how MdMYB73 and MdPH5 act to regulate vacuolar malate transport systems,thereby affecting malate accumulation and vacuolar pH.

Function, kinetic properties, crystallization, and regulation of microbial malate dehydrogenase

Malate dehydrogenase （MDH） is an enzyme widely distributed among living organisms and is a key protein in the central oxidative pathway. It catalyzes the interconversion between malate and oxaloacetate using NAD＋ or NADP＊ as a cofactor. Surprisingly, this enzyme has been extensively studied in eukaryotes but there are few reports about this enzyme in prokaryotes. It is necessary to review the relevant information to gain a better understanding of the function of this enzyme. Our review of the data generated from studies in bacteria shows much diversity in their molecular properties, including weight, oligomeric states, cofactor and substrate binding affinities, as well as differences in the direction of the enzymatic reaction. Furthermore, due to the importance of its function, the transcription and activity of this enzyme are rigorously regulated. Crystal structures of MDH from different bacterial sources led to the identification of the regions involved in substrate and cofactor binding and the residues important for the dimer-dimer interface. This structural information allows one to make direct modifications to improve the enzyme catalysis by increasing its activity, cofactor binding capacity, substrate specificity, and thermostability. A comparative analysis of the phylogenetic reconstruction of MDH reveals interesting facts about its evolutionary history, dividing this superfamily of proteins into two principle clades and establishing relationships between MDHs from different cellular compartments from archaea, bacteria, and eukaryotes.

Human lactate dehydrogenase and malate dehydrogenase possess the catalytic properties to produce aromatic α‑hydroxy acid

Lactate dehydrogenase and malate dehydrogenase are the two main alpha-hydroxy acid dehydrogenases in the human body.We investigated the catalytic properties of human lactate dehydrogenase LDHC,LDHL6A and malate dehydrogenase MDH1 on aromatic α-keto acids phenylpyruvic acid,p-hydroxyphenylpyruvic acid and 3,4-dihydroxyphenylpyruvic acid.The optimum temperatures for LDHC,LDHL6A,and MDH1 are 37℃,35℃,and 45℃,respectively;and the optimum pH is 6.5,6.5,and 5.5,respectively.The K_(m)of LDHC for phenylpyruvic acid and 3,4-dihydroxyphenylpyruvic acid were 0.90 mM and 0.92 mM,respectively.LDHL6A has a high affinity for phenylpyruvic acid and 3,4-dihydroxyphenylpyruvic acid with K_(m)of 0.77 mM and 0.80 mM,respectively;MDH1 has an extremely high affinity(K_(m)=0.46 mM)and catalytic efficiency(k_(cat)/K_(m)=23.87 s^(-1)·mM^(-1))for p-hydroxyphenylpyruvic acid.It also has a high affinity for 3,4-dihydroxyphenylpyruvic acid with a K_(m)of 0.90 mM,but with a low affinity for phenylpyruvic acid(K_(m)=3.76 mM).The catalytic properties of human LDHC,LDHL6A,and MDH1 for the abovementioned aromatic α-keto acids may be one of the sources of L-phenyllactic acid,L-p-hydroxyphenyllactic acid,and L-3,4-dihydroxyphenyllactic acid in humans.

血清Irisin、PTX3及MALAT1水平与糖尿病视网膜病变病情程度的关系及联合诊断价值

目的研究血清鸢尾素(Irisin)、长正五聚蛋白3(PTX3)、人肺腺癌转移相关转录本1(MALAT1)水平与糖尿病视网膜病变(DR)病情程度的关系及联合诊断的价值。方法选取2022年4月至2023年4月沧州市中心医院2型糖尿病(T2DM)合并DR患者85例设为DR组,85例单纯T2DM患者设为非DR组,同时期85例健康志愿者设为对照组。将DR组患者以是否处于增生型DR为标准分为增生型组(38例)与非增生型组(47例)。收集DR组患者病例临床资料,包括性别、舒张压、年龄、收缩压、病程、空腹血糖(FPG)、体质量指数、糖化血红蛋白(HbA1c)、吸烟史、甘油三酯(TG)、饮酒史、收缩期峰值流速、舒张末期峰值流速、阻力指数、空腹胰岛素(FINS)、糖尿病家族史、总胆固醇(TC)、胰岛素抵抗指数(HOMA-IR)。酶联免疫吸附法检测各组患者血清Irisin、PTX3水平,实时荧光定量PCR法检测血清MALAT1水平。采用Pearson相关性分析检测血清Irisin、PTX3及MALAT1水平与DR患者病情程度的相关性。Logistic回归分析DR患者病情程度的影响因素。受者工作特征曲线(ROC曲线)分析血清Irisin、PTX3及MALAT1单独诊断DR的价值。ROC曲线、净重新分类指数(NRI)及综合判别改善指数(IDI)分析含与不含血清Irisin、PTX3及MALAT1方案诊断DR的价值。结果3组患者血清Irisin、PTX3、MALAT1水平比较,差异均有统计学意义(均为P<0.001)。增生型组患者病程长于非增生型组,收缩期峰值流速、舒张末期峰值流速、血清Irisin水平均低于非增生型组,阻力指数、FPG、HbA1c、TG、FINS、HOMA-IR及血清PTX3、MALAT1水平均高于非增生型组,差异均有统计学意义(均为P<0.05)。DR患者血清Irisin水平与DR病情程度呈负相关(r=-0.512,P<0.001),PTX3、MALAT1水平与DR病情程度均呈正相关(r=0.497、0.573,均为P<0.05)。Logistic回归分析结果显示,病程、FPG、HbA1c、TG、FINS、HOMA-IR、收缩期峰值流速、舒张末期峰值流速、阻力指数及血清Irisin、PTX3、MALAT1水平均为DR病情程度加重的影响因素(均为P<0.05)。血清Irisin、PTX3、MALAT1诊断DR的曲线下面积(AUC)分别为0.743、0.811、0.773。与常规诊断方案比较,含有血清Irisin、PTX3、MALAT1水平的新诊断方案的AUC明显增大(Z=2.708,P=0.007),NRI、IDI分别为0.039(95%CI:0.022~0.069)、0.026(95%CI:0.014~0.047)(均为P<0.05)。结论DR患者血清Irisin水平降低,PTX3、MALAT1水平升高,且与患者DR病情程度密切相关,含有血清Irisin、PTX3、MALAT1指标的诊断方案具有较高的诊断价值。

lncRNA MALAT1调控GPx3去甲基化参与非小细胞肺癌的发生发展

目的探讨长链非编码RNA(lncRNA)MALAT1通过调控谷胱甘肽过氧化物酶3(GPx3)对非小细胞肺癌(NSCLC)增殖与侵袭的影响及其机制。方法通过TCGA数据库分析NSCLC患者的mRNA表达信息、甲基化数据及其临床信息,确定关键基因MALAT1与GPx3在NSCLC中的表达差异及其与患者预后之间的关系。采用免疫组织化学染色评估GPx3在肺腺癌组织中的表达水平,通过细胞培养、实时定量PCR、MTT法检测细胞增殖、细胞克隆形成以及迁移与侵袭能力来研究抑制MALAT1表达对A549细胞增殖与侵袭能力的影响。蛋白免疫印迹实验用于检测相关蛋白表达的变化。结果在NSCLC组织中,MALAT1的表达显著升高且与患者不良预后相关;GPx3的表达水平则显著降低,GPx3低表达患者的总生存率显著低于高表达组。其中MALAT1高甲基化水平与肺腺癌发生发展关系密切。沉默MALAT1可显著抑制肺癌细胞的增殖、克隆形成以及迁移和侵袭能力,同时促进GPx3的表达。蛋白表达分析进一步证实MALAT1的沉默减少了肿瘤干细胞标志物的表达,并抑制了上皮-间充质转化(EMT)过程。MALAT1通过募集LSD2调控GPx3的表达,从而在NSCLC的发展中发挥关键作用。结论lncRNA MALAT1通过抑制GPx3表达,促进NSCLC肿瘤细胞的增殖与侵袭能力。MALAT1高表达及高甲基化水平与NSCLC患者不良预后之间存在密切关联,为NSCLC的早期诊断、治疗及预后评估提供了新的生物标志物。