Mathematical Modeling of Sucrose Hydrolysis with Product and Substrate Inhibition

In this work, the enzymatic hydrolysis reaction of sucrose through invertase under unsteady-state conditions has been investigated. The aim is to evaluate the inhibition phenomena influence on the reaction rate and, then, on the concentration and temperature profiles by simulating the process in a tubular reactor, varying the enzyme concentration and the reactant mixture velocity. The transport phenomena considered during the enzymatic hydrolysis process have been described by means of unsteady-state momentum, mass and energy balance equations, taking into account molecular and convective transport and generation terms. Interpretation and discussion of the results obtained by FEM resolution of PDEs involved allow to understand the relevance of the operating parameters.

Analytical Expressions for Steady-State Concentrations of Substrate and Product in an Amperometric Biosensor with the Substrate Inhibition—The Adomian Decomposition Method

A mathematical model of an amperometric biosensor with the substrate inhibition for steady-state condition is discussed. The model is based on the system of non-stationary diffusion equation containing a non-linear term related to non-Michaelis–Menten kinetics of the enzymatic reaction. This paper presents the analytical expression of concentrations and current for all values of parameters φ2s φ2s α and β . Here the Adomian decomposition method (ADM) is used to find the analytical expressions for substrate, product concentration and current. A comparison of the analytical approximation and numerical simulation is also presented. A good agreement between theoretical predictions and numerical results is observed.

Alleviated photoinhibition on nitrification in the Indian Sector of the Southern Ocean

Nitrification,a central process in the marine nitrogen cycle,produces regenerated nitrate in the euphotic zone and emits N_(2)O,a potent greenhouse gas as a by-product.The regulatory mechanisms of nitrification in the Southern Ocean,which is a critical region for CO_(2)sequestration and radiative benefits,remain poorly understood.Here,we investigated the in situ and dark nitrification rates in the upper 500 m and conducted substrate kinetics experiments across the Indian Sector in the Cosmonaut and Cooperation seas in the late austral summer.Our findings indicate that light inhibition of nitrification decreases exponentially with depth,exhibiting a light threshold of 0.53%photosynthetically active radiation.A positive relationship between dark nitrification and apparent oxygen utilization suggests a dependence on substrate availability from primary production.Importantly,an increased NH_(4)^(+) supply can act as a buffer against photo-inhibitory damage.Globally,substrate affinity(α)increases with depth and transitions from light to dark,decreases with increasing ambient NH_(4)^(+)and exhibits a latitudinal distribution,reflecting substrate utilization strategies.We also reveal that upwelling in Circumpolar Deep Water(CDW)stimulates nitrification through the introduction of potentially higher iron and deep diverse nitrifying microorganisms with higherα.We conclude that although light is the primary limiting factor for nitrification in summer,coupling between substrate availability and CDW upwelling can overcome this limitation,thereby alleviating photoinhibition by up to 45%±5.3%.

Kinetic and binding equilibrium studies of dihydroflavonol 4-reductase from Vitis vinifera and its unusually strong substrate inhibition

Dihydroflavonol 4-reductase (DFR), a member of the short-chain dehydrogenase family, catalyzes the last common step in the biosynthesis of flavan-3-ols and condensed tannins. Initial rates of DFR were measured by monitoring the 340-nm absorbance decrease resulting from the joint consumption of dihydroquercetin (DHQ) and NADPH, as a function of pH, temperature and ionic strength. At pH 6.5 and 30o C, substrate inhibition was observed above 30 μM DHQ. At lower/non-inhibitory DHQ concentrations, NADP+ behaves as a competitive inhibitor with respect to NADPH and as a mixed inhibitor with respect to DHQ, which supports a sequential ordered mechanism, with NADPH binding first and NADP+ released last. Binding-equilib-rium data obtained by means of the chromatographic method of Hummel and Dreyer at pH 7.5 and by isothermal calorimetric titration at pH 6.5 led to the conclusion that ligands of the apoenzyme included NADPH, NADP+ and DHQ. The mechanism which best accounts for substrate inhibition at pH 6.5 in the absence of product involves the formation of a binary non-productive E.DHQ complex. Thus, a productive ternary complex cannot be formed when DHQ binds first. This mechanism of inhibition may prevent the accumulation of unstable leucoanthocyanidins within cells.

Enhancement of α-ketoisovalerate production by relieving the product inhibition of L-amino acid deaminase from Proteus mirabilis

L-Amino acid deaminase(LAAD) is a key enzyme in the deamination of L-valine(L-val) to produce α-ketoisovalerate(KIV). However, the product inhibition of LAAD is a major hindrance to industrial KIV production.In the present study, a combination strategy of modification of flexible loop regions around the product binding site and the avoidance of dramatic change of main-chain dynamics was reported to reduce the product inhibition.The four mutant PM-LAAD^(M4)(PM-LAAD^(S98A/T105A/S106A/L341A)) achieved a 6.2-fold higher catalytic efficiency and an almost 6.7-fold reduction in product inhibition than the wild-type enzyme. Docking experiments suggested that weakened interactions between the product and enzyme, and the flexibility of the "lid" structure relieved LAAD product inhibition. Finally, the whole-cell biocatalyst PM-LAAD^(M4) has been applied to KIV production,the titer and conversion rate of KIV from L-val were 98.5 g·L^-1 and 99.2% at a 3-L scale, respectively. These results demonstrate that the newly engineered catalyst can significantly reduce the product inhibition, that making KIV a prospective product by bioconversion method, and also provide the understanding of the mechanism of the relieved product inhibition of PM-LAAD.

Synthesis and NO production inhibition of novel Mannich base derivatives of irisolidone

Five new C-8 Mannich base derivatives of irisolidone 2a-2e were synthesized and their nitric oxide（NO）production inhibitory activity was evaluated.Compounds 2a,2b,2c and 2e displayed stronger activities in vitro than the parent compound irisolidone.

Effect of initial substrate and biomass concentrations on anaerobic fermentative hydrogen production in batch reactors

The effects of initial substrate (5-60 g /L) and biomass concentration (0.5-3 g /L) on fermentative hydrogen production by mixed cultures were investigated in batch tests using glucose as substrate.The experimental results showed that the hydrogen production increases as the initial substrate concentration increases from 0 to 25 g /L.It indicated that the shift in the metabolic pathway or in the composition of the bacterial flora occurs.The maximum hydrogen yield of 1.78 mol /mol-glucose is obtained at the substrate concentration of 15 g /L.This study also shows that initial biomass concentration affects the hydrogen yield as the cumulative hydrogen production has been increased with the increase of initial cell concentration up to 1.5 g /L and reached the highest level.The maximum hydrogen yield is obtained at the cell concentration of 1.5 g /L.It indicated that the optimum biomass /substrate ratio,maximizing the hydrogen yield and the hydrogen production rate,is determined to be 0.1 g biomass /g glucose.

Hydrolysis of Raw Corn Starch Granules by Glucoamylase and Product Inhibition During the Hydrolysis

Raw corn starch granules were hydrolysized by glucoamylase in a chemostat. The hydro- lysis of three different-sized granules shows that smaller granules undergo more hydrolyzation than larger ones. After 78 h, 9700 of the granules was hydrolysized with diameter between 0.15 mm and 0.3 mm at 50 ℃. When corn starch concentration increased from 100 g/L to 250 g/L, the amount of reducing sugar produced was proportional to the initial substrate concentration and no substrate inhibition phenomenon appeared. In order to study the product inhibition exactly, the product from hydrolysis reaction itself was added into the hydrolysis system at the beginning of starch hydrolysis. Product inhibition with different quantities of product added were studied in the initial several hours, during which period enzyme inactivation could be neglected and product inhibition could be studied separately. The experiments indicate that product inhibition happens when the additional quantity exceeds 9.56 g/L.

Improvement of Concrete Properties and Reinforcing Steel Inhibition Using a Natural Product Admixture

The use of a natural white juice, taken from magrabe banana stem, as concrete admixture to improve mechanical and physicrvchemical properties of concrete has been studied. The compressive strength, bulk density the free lime liberated during hydration and the combined water content were determined. The results indicate that the admixture acts as a retarder in most cases and as accelerator in some ones. Also, the admixture effect on the corrosion resistance of the reinforcing steel against surrounding aggressive media has been investigated using galvanostatic polarization technique. The addition of 0.2% admixture leads to the more inhibition of the steel

Product of the Schistosoma mansoni Glutathione Peroxidase Gene is a Selenium ContainingPhospholipid Hydroperoxide Glutathione Peroxidase (PHGPx) Sharing MolecularWeight and Substrate Specificity WithIts Mammalian Counterpart

In the blood fluke Schistosoma mansoni a functionally active, monomeric, phospholipid hydroperoxide glutathione peroxidase (PHGPx) has been purified and characterized. This enzyme contains a catalytically active selenocysteine. The protein has been shown to be the product of a cloned gene, previously referred to as a glutathione peroxidase gene. S. mansoni PHGPx has been found 5 times more abundant in female than in male worm extract. As in vertebrate PHGPx, homology alignment indicates that the residues involved in the glutathione binding by the tetrameric cellular glutathione peroxidase are mutated in the S. mansoni enzyme. Thus, this aspect appears a landmark of the PHGPx-type of glutathione peroxidases,which might be of functional relevance

A soluble FcγR homolog inhibits Ig M antibody production in ayu spleen cells

Classical Fc receptors (FcRs) mediate the binding to and recognition of the Fc portion of antibodies and play an important role during immune responses in mammals. Although proteins similar to soluble FcRs have been identified in fish, little is known about the role of such proteins in fish immunity. Here, we cloned a cDNA sequence encoding a soluble Fc receptor for an immunoglobulin G (FcγR) homolog from ayu (Plecoglossus altivelis)(PaFcγRl). The predicted protein was composed of two immunoglobulin C2-like domains but lacked a transmembrane segment and a cytoplasmic tail. The PaFcγRl transcripts were distributed at low levels in all tested tissues, but significantly increased after Vibrio anguillarum infection. The PaFcγRl protein was expressed in the head kidney, trunk kidney, and neutrophils. Recombinant PaFcγRl (rPaFcγRl) was secreted when transfected into mammalian cells and the native protein was also detected in serum upon infection. rPaFcγRl was also demonstrated to bind to ayu IgM, as assessed by cell transfection. Suppressive activity of the recombinant mature protein of PaFcγRl (rPaFcγRlm) on in vitro anti-sheep red blood cell (SRBC) responses was detected by a modified hemolytic plaque forming cell assay. In conclusion, our study revealed that PaFcγRl is closely involved in the negative regulation of IgM production in the ayu spleen.

Evaluation of the effect of compound aqueous solubility in cytochrome P450 inhibition assays

It is a common practice in drug discovery organizations to screen new chemical entities in order to predict future drug-drug interactions. For this purpose, there are two main assay strategies, one based on recombinant cytochrome P450 (rCYP) enzymes and fluorescent detection, and other on human liver microsomes (HLM) and liquid chromatography coupled to mass spectrometry. Many authors have reported a poor correlation between both technologies, giving rise to concerns about the usefulness of fluorometric methods for predicting drug-drug interactions. In this study, we investigated the role that compound aqueous kinetic solubility may play in this lack of correlation. We found that drug discovery compounds with unacceptable kinetic solubility, measured by a turbidimetric solutibility assay, tended to yield higher IC50 values in in vitro models based on human liver microsomes, whereas compounds with kinetic solubility values higher than 50 μM showed very similar IC50 values in both in vitro models. Our results show that the turbidimetric solubility assay is a useful tool to identify those discovery compounds that may require further investigation in order to avoid overlooking future drug-drug interactions.

Subfunctionalization of a monolignol to a phytoalexin glucosyltransferase is accompanied by substrate inhibition

Uridine diphosphate-dependent glycosyltransferases(UGTs)mediate the glycosylation of plant metabolites,thereby altering their physicochemical properties and bioactivities.Plants possess numerous UGT genes,with the encoded enzymes often glycosylating multiple substrates and some exhibiting substrate inhibition kinetics,but the biological function and molecular basis of these phenomena are not fully understood.The promiscuous monolignol/phytoalexin glycosyltransferase NbUGT72AY1 exhibits substrate inhibition(Ki)at 4 mM scopoletin,whereas the highly homologous monolignol StUGT72AY2 is inhibited at 190 mM.We therefore used hydrogen/deuterium exchange mass spectrometry and structure-based mutational analyses of both proteins and introduced NbUGT72AY1 residues into StUGT72AY2 and vice versa to study promiscuity and substrate inhibition of UGTs.A single F87I and chimeric mutant of NbUGT72AY1 showed significantly reducedscopoletin substrate inhibition,whereas its monolignolgly cosylation activity was almost unaffected.Reverse mutations in StUGT72AY2 resulted in increased scopoletin glycosylation,leading to enhanced promiscuity,which was accompanied by substrate inhibition.Studies of 3D structures identified open and closed UGT conformers,allowing visualization of the dynamics of conformational changes that occur during catalysis.Previously postulated substrate access tunnels likely serve as drainage channels.The results suggest a two-site model in which the second substrate molecule binds near the catalytic site and blocks product release.Mutational studies showed that minor changes in amino acid sequence can enhance the promiscuity of the enzyme and add new capabilities such as substrate inhibition without affecting existing functions.The proposed subfunctionalization mechanism of expanded promiscuity may play a role in enzyme evolution and highlights the importance of promiscuous enzymes in providing new functions.

我国设施生态农业主要模式及配套技术的研究与实践

设施生态农业是指在设施种植和设施养殖中采用清洁、绿色、健康生产方式,以提高资源利用效率、农产品产量与质量、环境效益为目标的生态农业模式。2002年农业部重点推广的设施生态农业模式主要有两大类:一类是种养沼三结合的“四位一体”生态模式,从最初以农户为单位的单体日光温室到以村庄为单位的种养结合生态温室群模式,拓展到在一个大区域内将大型猪场的粪污进行工业化沼气并网发电,沼液通过管道输送到农田来减少化肥施用和改良土壤的宏观生态农业模式,相关的结构配置、配套的种养殖技术和装备也在不断研发和提升中。另一类是采用综合性生态农业技术的设施生态农业模式,包括:采用各类立体/垂直栽培技术提高土地资源利用率;通过各种轮作栽培技术减少设施蔬菜土壤连作障碍和降低农药使用量;采用土壤健康栽培技术,通过有机肥的合理施用改善土壤性状;采用有机基质栽培技术,用农林废弃物发酵后的物料作为栽培基质为作物提供养分;采用覆盖防虫网、色板诱杀、灯光诱杀、高温封棚、蒸气消毒、有色膜覆盖土壤、天敌昆虫生物防治等病虫草害生态防治技术来减少有害生物发生。期望通过相关配套装备技术的进一步研发提高设施生态农业的信息化、自动化水平,实现设施农业的可持续发展。

肉制品中晚期糖基化终末产物研究进展

肉类富含蛋白质和脂质,有利于晚期糖基化终末产物(AGEs)的生成。研究表明,AGEs会对人体产生多种危害,应尽量减少其在加工过程中的生成量。本文对近年来食品中尤其是肉制品中AGEs的形成、危害、检测进行介绍,并综述影响肉制品中AGEs生成量的因素,以期为探究减少肉制品加工过程中AGEs生成量的新方法提供思路。

抑制活菌泡菜贮藏过程中品质劣变的研究

目的:研究活菌泡菜产品在贮藏流通过程中由微生物引起的产品品质变化,开发延长泡菜贮藏期的新方法。方法:对从泡菜中分离鉴定出来的8种乳酸菌,在不同pH培养基条件下检测各种乳酸菌生长速度。对8种乳酸菌进行产气测定。在发酵前添加泡菜汁、嗜酸乳杆菌、植物乳杆菌、木糖醇等,在不同温度条件下发酵和贮藏,对泡菜的色泽进行评分,对酸度、混浊度、挥发性物质进行测定。结果:在pH 4.5时,植物乳杆菌是优势菌,其次是短乳杆菌。在pH 4.0~3.0时,嗜酸乳杆菌是优势菌,其次是植物乳杆菌,主要产气菌是短乳杆菌、假肠膜明串珠菌、坏发酵乳杆菌。pH 4.0~4.5时,主要产气菌是短乳杆菌。在pH 3.5时,主要是坏发酵乳杆菌产气。在pH 3.0时,不容易产气。发酵前添加2 mL/L 1×10~5CFU/mL植物乳杆菌和20 mg/g木糖醇,可显著延长常温和低温下泡菜的贮藏期和货架期。结论:1×10~5CFU/mL植物乳杆菌和20 mg/g木糖醇处理,显著抑制常温贮藏泡菜的总挥发物积累,抑制泡菜的异硫氰酸烯丙酯、萘类积累,有利于维持原初气味特征。

离子交换树脂法规模化生产乳源酪蛋白糖巨肽及其对流感病毒的血凝抑制活性

目的:优化规模化生产乳源酪蛋白糖巨肽(CGMP)的工艺条件,并探讨其对流感病毒的血凝抑制能力。方法:以阴离子交换树脂为分离介质,唾液酸含量为产品的活性检测指标,分别从上样体积、上样流量、洗脱液浓度、洗脱液体积和树脂使用周期5个工艺条件,在前期小试和中试的基础上,考察从乳清粉中规模化生产CGMP;同时利用血球凝集抑制试验验证产品CGMP对流感病毒的抑制活性。结果:优化的CGMP产品技术路线为上样体积3BV、上样流量0.8 L/min、洗脱体积1BV、洗脱液浓度0.6 mol/L、树脂适宜使用周期4次。该工艺条件下处理乳清粉溶液体积为108 L(2160 g)、树脂36 L,得到CGMP产品21.183 g,得率为0.981 g/100 g,产品纯度为89.032%,回收率为51.972%,唾液酸含量为21.503 g/100 g,蛋白CGMP产品对流感病毒A(H1N1)和流感病毒B的最低抑制质量浓度分别为1.0000,1.2500 mg/mL。结论:利用优化的技术路线生产获得CGMP产品的纯度和唾液酸含量均优于市售商品CGMP,且对流感病毒有明显的抑制作用。

猪细小病毒血凝抑制试验抗原、阳性血清与阴性血清的制备与鉴定

猪细小病毒(Porcine parvovirus,PPV)血凝抑制试验抗原、阳性血清和阴性血清在猪细小病毒制品的效力检验中不可或缺,对猪细小病毒相关生物制品的质量控制至关重要。试验采用PPV 7909株病毒同步接种PK-15细胞制备血凝抑制试验抗原,用制备的抗原乳化后免疫豚鼠制备阳性血清,同时用未免疫的阴性豚鼠制备阴性血清。对抗原、阳性血清和阴性血清进行鉴定,结果表明,制备的PPV血凝抑制试验抗原HA效价达1∶512;阳性血清HI效价达1∶1024;阴性血清HI效价小于1∶8,且特异性均良好。用制备的HI试验抗原与不同PPV疫苗株的阳性血清进行HI试验,同时,用制备的阳性血清、阴性血清与不同PPV疫苗株的灭活抗原进行HI试验。结果表明,制备的抗原与阳性血清具备良好的血清学交叉反应性,制备的阴性血清与不同疫苗株抗原均呈阴性反应,可用于PPV制品的统一评价。

数字经济与中国企业出口产品质量:理论机制与经验事实

本文通过拓展Antoniades(2015)的异质性企业模型发现数字经济的发展能够通过创新促进效应和竞争抑制效应影响企业出口产品质量,前者提高了出口产品质量,后者则降低了出口产品质量。基于中国工业企业数据、海关数据和企业专利数据的实证分析表明,在两种效应的共同作用下,数字经济的发展提高了企业出口产品质量,且企业生产率在该过程中发挥着正向调节作用。

试析生成式AI对媒介内容生产的生态级革命

生成式AI技术作为一种可感知、重体验、易操作的模型系统,带来了全新的智能生产浪潮,在媒介内容生产领域正在发挥着越来越重要的作用,媒介内容生产机制和传媒业态都将迎来巨大变革。为进一步认识生成式AI对媒介内容生产带来的影响,文章梳理媒介内容生产的演变过程,结合生成式AI的技术特点和应用潜力,重点分析生成式AI对媒介内容生产的底层赋能和在媒介内容生产的宏观思维层面、中观组织层面、微观操作层面的转型升级,并对生成式AI赋能媒介内容生产所面临的风险挑战及如何把握好人机互构过程中人类主体性这一价值锚点给出借鉴性思考。