Measuring phosphatidic acid phosphohydrolase (EC 3.1.3.4) activity using two phosphomolybdate-based colorimetric methods

Phosphatidic acid phosphohydrolase (3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4), also known as PAP, catalyzes the dephosphorylation of phosphatidic acid (PtdOH) to form diacylglycerol (DAG) and inorganic orthophosphate. In eukaryotes, the PAP driven reaction is the committed step in the synthesis of triacylglycerol (TAG). Existing methods for measuring PAP activity rely on the use of radioactive PtdOH. These methods are costly and cumbersome. In this report, we describe a simple assay procedure to measure released inorganic orthophosphate, which is a coproduct of the PAP reaction. Each molecule of PtdOH would release one molecule of DAG and one molecule of inorganic orthophosphate (Pi) when subjected to enzymatic breakdown under optimal conditions. Given the published rates of in vitro PAP enzymatic activity from various sources, we proposed that colorimetric determination of released Pi is possible. With this view, we performed in vitro PAP activity assays using freshly isolated enzyme from bitter gourd, Momordica charantia, and measured the released Pi using two spectrophotometric methods. Both methods gave about 2.0 to 2.25 ηkat per mg of protein. Thus, it is now possible to perform PAP activity using a simple procedure that uses nonradioactive substrates, provided the sample is dialyzed extensively to lower the intrinsic concentration of free phosphate. The kinetics data presented in this study is comparable to that of other PAP enzymes reported elsewhere, which gives credence to the notion that non-radioactive methods can be used to perform PAP activity.

Purification, characterization, and bioinformatics studies of phosphatidic acid phosphohydrolase from <i>Lagenaria siceraria</i>

Phosphatidic acid phosphohydrolase (PAP), EC 3.1.3.4, is the penultimate step in the Kennedy pathway of triacyl glycerol (TAG) synthesis leading to the formation of diacylglycerol (DAG), which is a key intermediate in TAG synthesis. We partially purified a soluble PAP from mid maturing seeds of bottle gourd, Lagenaria siceraria. The steps include both anionic and cationic ion exchanger columns. Catalytic characterization of the partially purified PAP revealed that the optimum pH and temperature for activity were at 5.5?C and 45?C. Under optimum assay condition using dioleoyl phosphatidic acid (DPA) as the substrate, the Vmax and Km were 0.36 ηkat/mg of protein and 200 μM, respectively. For the synthetic substrate, ρ-nitrophenylphosphate, ρ-NPP, the Vmax and Km were 33.0 nkat/mg of protein and 140 μM, respectively. The activity was neither inhibited nor enhanced by the presence of Mg2+ at a concentration range of 0 to 10 mM. Two major protein bands at 42-kDa and 27-kDa were visible in SDS-PAGE after partial purification. Bioinformatics analysis of tryp-sinized protein fractions containing PAP activity showed peptide sequences with sequence homology to various phosphate metabolizing enzymes including cucumber and castor bean purple acid phosphatase, polyphosphate kinase, fructose biphosphate aldolase, and enolase from various dicotyledonous plants including rice, corn, grape, and Arabidopsis lyrata.

Identification of an Mg2+-Independent Soluble Phosphatidate Phosphatase in Cottonseed (Gossypium hirsutum L.)

Cotton (Gossypium hirsutum L.) provides a major source of oil for food and feed industries, but little was known about the enzymes in the oil biosynthesis pathway in cottonseed. We are interested in a better understanding of enzymatic components for oil accumulation in cottonseed. The objective of this study was to identify one key enzyme in oil biosynthesis pathway: phosphatidic acid phosphatase (PAP, 3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4). PAP hydrolyzes the phosphomonoester bond in phosphatidate yielding diacylglycerol and Pi. PAPs are generally categorized into Mg2+-dependent soluble PAP and Mg2+-independent membrane-associated PAP. Cottonseed from 25 - 30 days post anthesis was used for the study. The results showed that an Mg2+-independent soluble PAP activity was identified from the cottonseed. While the microsomal fraction of the extract provided only 9% of the PAP activity, 69% of the PAP activity was associated with the cytosol. The PAP activity correlated well with enzyme concentration and incubation time. The pH and temperature optima of the enzyme were pH 5 and 55℃, respectively. Under optimized assay conditions, the Vmax and Km values of cottonseed PAP for dioleoyl phosphatidic acid as the substrate were 2.8 nkat/mg of protein and 539 μM, respectively. Inclusion of the detergent Triton X-100 (0% - 0.5%) or magnesium chloride (1 mM) in the reaction mix did not alter activity to a significant degree. This is the first report of a PAP activity in the seeds of Gossipium hirsutum. This study should provide a basis for purification and characterization of this important enzyme from cottonseed in the future.

Involvement of phosphatidate phosphatase in the biosynthesis of triacylglycerols in Chlamydomonas reinhardtii

Lipid biosynthesis is essential for eukaryotic cells, but the mechanisms of the process in microalgae remain poorly understood. Phosphatidic acid phosphohydrolase or 3-sn-phosphatidate phosphohydrolase(PAP) catalyzes the dephosphorylation of phosphatidic acid to form diacylglycerols and inorganic orthophosphates. This reaction is integral in the synthesis of triacylglycerols. In this study, the mRNA level of the PAP isoform CrPAP2 in a species of Chlamydomonas was found to increase in nitrogen-free conditions. Silencing of the CrPAP2 gene using RNA interference resulted in the decline of lipid content by 2.4%–17.4%. By contrast, over-expression of the CrPAP2 gene resulted in an increase in lipid content by 7.5%–21.8%. These observations indicate that regulation of the CrPAP2 gene can control the lipid content of the algal cells. In vitro CrPAP2 enzyme activity assay indicated that the cloned CrPAP2 gene exhibited biological activities.

Contribution of microbial phytases to the improvement of plant growth and nutrition: A review

Phytases belong to the class of phosphohydrolases that begin the step-wise hydrolysis of phosphates from phytates. Phytates are a derivative of myo-inositol, which is the primary storage form of organic phosphorus in plant cells. Phytase has been used globally to diminish phosphorus pollution and to enhance nutrition in monogastrics. In this review, the classification, sources, and diversity of microbial phytases, and their practical applications, as well as supplementation of the soil with transgenic and wild types of microbial strains, which can release phytase to enhance phosphorus availability for plant uptake and reduce the need for fertilizers, are discussed. The overexpressed microbial phytases in transgenic plants enhance the growth capacity of co-cultivated plants and can therefore be employed in agricultural and biotechnological practices, such as intercropping. The introduction of phytases into the soil for improved plant growth and enhanced crop yield can be accomplished without extra cost. A diverse group of photoautotrophic microalgae can synthesize phytase and will likely be useful in many human food and animal industries.

Protective effect of resveratrol on rat cardiomyocyte H9C2 cells injured by hypoxia/reoxygenation by regulating mitochondrial autophagy via PTEN-induced putative kinase protein 1/Parkinson disease protein 2 signaling pathway

OBJECTIVE:To investigate the protective effect of resveratrol on cardiomyocytes after hypoxia/reoxygenation intervention based on PTEN-induced putative kinase protein 1/Parkinson disease protein 2(PINK1/PARKIN)signaling pathway.METHODS:3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used to detect the effect of resveratrol on the viability of H9C2 cells;the hypoxia/reoxygenation(H/R)model was established in tri-gas incubator;2’,7’-Dichlorofluorescin diacetate staining was used to measure the content of reactive oxygen species(ROS);the changes of mitochondrial membrane potential was determined by 5,5’,6,6’-Tetrachloro-1,1’,3,3’-tetraethyl-imidacarbocyanine iodide staining;the changes of mitochondrial respiratory chain complex activity was evaluated by enzyme activity kits;flow cytometry was used to detect the ratio of apoptotic cells;transmission electron microscope was used to observe the ultrastructure of H9C2 cells;Western blot was used to detect the protein changes of mitochondrial 20 k Da outer membrane protein(TOM20),translocase of inner mitochondrial membrane 23(TIM23),presenilins associated rhomboid-like protein(PARL),PINK1,PARKIN and mitofusin 1(Mfn1),mitofusin 2(Mfn2),phosphotyrosine independent ligand for the Lck SH2 domain of 62 k Da(P62),microtubule-associated protein 1 light chain 3 beta(LC3B);the m RNA levels of PINK1 and PARKIN was detected by quantitative polymerase chain reaction;immunoprecipitation assay was used to detect the interaction between PARKIN and Ubiquitin.RESULTS:Resveratrol could inhibit the proliferation of H9C2 cells in a time-and concentration-dependent manner;however,pretreatment with low cytotoxic resveratrol could reduce the H/R-induced increase in cellular ROS levels,alleviate the loss of mitochondrial membrane potential induced by H/R,inhibit H/R-induced apoptosis of H9C2 cells,and protect the mitochondrial structure and respiratory chain of H9C2 cells from H/R damage.Resveratrol could further increase the levels of p62,PINK1,PARKIN protein,the expression of PINK1,PARKIN m RNA and the ratio of LC3BⅡ/LC3BⅠin H/Rinduced H9C2 cells,inhibit the interaction between PARKIN and Ubiquitin in H/R-induced H9C2 cells,and further reduce the expression of TOM20,TIM23,PARL,Mfn1 and Mfn2 protein in H/R-induced H9C2 cells.The effect of resveratrol is consistent with that of autophagy activator on H/R-induced H9C2 cells.CONCLUSIONS:Resveratrol can protect H9C2 cells from H/R injury,which may be related to resveratrol promoting mitochondrial autophagy by activating PINK1/PARKIN signaling pathway.

Effect of compound Guizhu capsule on phosphate and tension homology deleted on chromsome ten and murine double mimute 2 gene expression in lung cancer of mice

OBJECTIVE: To observe the inhibitory effect of the Chinese herbal compound Guizhu capsule(CGZC)on lung cancer and explore the possible mechanism underlying its actions by evaluating its effects on the expression of phosphate and tension homology deleted on chromsome ten(PTEN) and murine double mimute 2(MDM2) in lung cancer model mice.METHODS: A mouse model of transplanted lung cancer was established by subcutaneous inoculation of cancer cells into the axillae of mice. Twenty-four hours later, the mice were weighed and randomly divided into the model control group, cisplatin group(DDP group), and high, moderate and low dosage CGZC groups, with ten mice in each group. The control mice received an equal volume of distilled water. DDP was intraperitoneally injected at 1 mg/kg in the DDP group, once a day for 3days. CGZC diluted with distilled water was admin-istered at 20 g/kg(10 times the clinical adult dosage) in the high-dose group, 10 g/kg(5 times the clinical adult dosage) in the moderate-dose group and 5 g/kg(2.5 times the clinical adult dosage) in the low-dose group once a day for 10 days. On the11 th day, the mice were weighed and killed. The tumor tissues were weighed and the tumor inhibition rate was calculated. PTEN and MDM2 protein expression were detected by immunohistochemical analysis of tumor tissues.RESULTS: The CGZC high-and moderate-dose groups showed a significant inhibitory effect on tumor growth(P < 0.05); there was no significant difference between the high dose group and the DDP group(P > 0.05). The CGZC high-dose group also showed enhanced expression of PTEN protein(P <0.01) and decreased expression of MDM2 protein(P < 0.01) in lung cancer cells of the mice. There was no significant difference between the high dose group and the DDP group.CONCLUSION: CGZC has a significant inhibitory effect on transplanted lung cancer in mice. The mechanism may involve reducing expression of PTEN and decreasing the expression of MDM2 in the lung cancer tissues of the mice.

Fuzheng Kang'ai decoction(扶正抗癌方) inhibits cell proliferation,migration and invasion by modulating mir-21-5p/human phosphatase and tensin homology deleted on chromosome ten in lung cancer cells

OBJECTIVE:To elucidate the potential molecular mechanism by which Fuzheng Kang’ai decoction(扶正抗癌方,FZKA)inhibits proliferation,migration,and invasion of lung cancer cells.METHODS:Varying FZKA concentrations were used to manage lung cancer cells(A549 and PC9).We employed:cell counting kit-8(CCK-8)and plate clone formation assays to examine the cell viability;flow cytometry(FCM)to analyze the cycle arrest;transwell and woundhealing assays to assess the cell invasion and migration,respectively.Further,a quantitative real-time polymerase chain reaction(q RT-PCR)assay was adopted to evaluate the miR-21-5p expression.For protein expression analysis,we employed the Western blot technique.Recombinant miR-21-5p overexpression adenovirus vector harboring GFP was constructed and transfected into A549 and PC9,after which we explored the effect of FZKA on miR-21-5p overexpression.RESULTS:Notably,treatment with FZKA inhibited viability,clone-formation ability,invasion,and migration of lung cancer cells.Mechanistically,FZKA markedly suppressed miR-21-5p expression but elevated the human phosphatase and tensin homology deleted on chromosome ten(PTEN)protein level in both A549 and PC9 cells.Over-expression of miR-21-5p lowered PTEN protein expression.Besides,overexpressed miR-21-5p levels with adenovirus antagonized FZKA-upregulated PTEN protein expression.CONCLUSION:The present study demonstrates how FZKA modulates cell biological behaviors,for instance,it impedes the proliferation by upregulating PTEN expression with miR-21-5p as the target.These findings unveil the potential novel molecular mechanisms from the micro RNA aspect by which FZKA suppresses the growth of human lung cancer cells.

Mechanism of total glucosides from Chishao(Radix Paeoniae Rubra)on proliferation and apoptosis of hepatocellular carcinoma cells via phosphatase and tensin homolog deleted on chromosome ten/phosphatidylinositol 3-kinase/protein kinase B signaling pathway

OBJECTIVE:To investigate the possible molecular mechanism of total glycosides of Chishao(Radix Paeoniae Rubra)(TG-RPR)on proliferation and apoptosis of hepatocellular carcinoma cells.METHODS:The proliferation of TG-RPR on Hep G2 cells was detected using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)assay.The apoptosis of Hep G2 cells was measured by annexin V-FITC/double staining.The phosphatase and tensin homolog deleted on chromosome ten(PTEN)/phosphatidylinositol 3-kinase(PI3 K)/protein kinase B(Akt)signaling pathway was evaluated by Western Blot and reverse transcription-polymerase chain reaction(RT-PCR).RESULTS:TG-RPR can up-regulation the expression of pro-apoptotic factors such as PTEN and BCL2-Associated X(Bax),down-regulation the expression of anti-apoptotic factors including B-cell lymphoma-2(Bcl-2),PI3 K,and Akt.CONCLUSION:TG-RPR significantly inhibits the proliferation of Hep G2 cells in a dose-dependent manner and promotes apoptosis.These results demonstrated TG-RPR has significant inhibitory effect on Hep G2 cells.These results identify a critical role of TG-RPR in proliferation and apoptosis of Hep G2 cells via modulating PTEN/PI3 K/Akt signaling pathway.TG-RPR may offer a promise as a potential pharmaceutical therapy for hepatocellular carcinoma.