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Substrate (chemistry)

About: Substrate (chemistry) is a research topic. Over the lifetime, 35902 publications have been published within this topic receiving 740722 citations. The topic is also known as: enzyme substrate.


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Journal ArticleDOI
TL;DR: This mode of oxidation appears to be unique to substrates with a positively charged quaternary nitrogen; the hydroxylation of other nonaldehydic heterocyclic substrates for the human enzyme is sensitive to conventional aldehyde oxidase inhibitors.
Abstract: HUMAN LIVER ALDEHYDE OXIDASE (ALDEHYDE: O(2) oxidoreductase, EC 1.2.3.1) has been purified 60-fold and some of its properties studied. Like aldehyde oxidase from other mammalian species, human liver aldehyde oxidase is an enzyme with dual substrate specificity, possessing the ability to catalyze not only the oxidation of aldehydes to the corresponding carboxylic acids, but also the hydroxylation of a number of nonaldehydic heterocyclic compounds; its relative activity towards the latter group of substrates is low, however, when compared with that of liver aldehyde oxidase from rabbit and guinea pig. When the aromatic aldehyde benzaldehyde is used as substrate, human liver aldehyde oxidase, like the rabbit enzyme, is strongly inhibited by menadione, estradiol-17beta, antimycin A, Triton X-100, and N-alkylphenothiazines; the human enzyme differs from the rabbit enzyme, however, in being relatively insensitive to oligomycin and Amytal. Like the rabbit enzyme, the human enzyme can catalyze the 3-hydroxylation of phenazine methosulfate (PMS) and the 6-hydroxylation of N-methylnicotinamide (NMN). With the rabbit enzyme, however, the aerobic hydroxylation of these substrates proceeds by a conventional mechanism, while with the human enzyme, the aerobic hydroxylation of PMS and NMN is anomalous in that the reaction is inhibited only by agents with affinity for the substrate-binding site, such as cyanide and N-alkylphenothiazines, and not by agents which inhibit the "internal electron transport chain" of the enzyme, such as menadione and diethylstilbestrol. This mode of oxidation appears to be unique to substrates with a positively charged quaternary nitrogen; the hydroxylation of other nonaldehydic heterocyclic substrates for the human enzyme is sensitive to conventional aldehyde oxidase inhibitors.

145 citations

Journal ArticleDOI
TL;DR: The method of immobilization can overcome the problem of reduced permeability of xylan, a high molecular weight substrate, to its enzyme which is conventionally entrapped within the alginate beads.

145 citations

Journal ArticleDOI
TL;DR: A new and rapid continuous assay of rat liver microsomal UDP-glucuronyltransferase (EC 2.4.1.17) has been developed, and lipid solubility seems important for determining the conversion rate: poorly lipid-soluble substrates were glucuronidated only at a low rate and high lipid solube seems to be a prerequisite for high conversion rate.
Abstract: 1. A new and rapid continuous assay of rat liver microsomal UDP-glucuronyltransferase (EC 2.4.1.17) has been developed. It is based on measurement of UDP production from UDP-glucuronate during the glucuronidation reaction; UDP production was continuously measured by coupling it to the conversion of NADH into NAD+ through pyruvate kinase and lactate dehydrogenase. This assay is independent of the acceptor substrate used; several findings confirm its applicability. 2. The glucuronidation rate of a series of phenol derivatives was determined with this assay, by using a Triton X-100-activated microsomal preparation as enzyme source. Conjugation of a series of nitrophenol derivatives was also investigated by the 'classical' assay (measurement of disappearance of the yellow colour of the nitrophenol during glucuronidation). The substrate with the highest conversion rate was 3-methyl-2-nitrophenol. 3. Both electron releasing and electron withdrawing ring substituents increased the glucuronidation rate of the phenol derivatives, as compared with phenol. 4. Lipid solubility seems important for determining the conversion rate: poorly lipid-soluble substrates were glucuronidated only at a low rate and high lipid solubility seems to be a prerequisite for high conversion rate. Glucuronidation of poorly lipid-soluble compounds may be limited by diffusion. 5. The consequences of these findings for the interpretation of studies on heterogeneity of the enzyme are discussed.

145 citations

Journal ArticleDOI
TL;DR: In 68 men 23 to 45 years old, whose semen analyses were normal, the seminal plasma maltase activity was generally decreased in patients with infertility disorders, and isomaltase appeared to be absent from seminal plasma.
Abstract: Hitherto, seminal plasma maltase has been measured with maltose as substrate; this method is time consuming and lacks specificity. The use of a synthetic substrate, p-nitrophenol-alpha-D-glucopyranoside, allows accurate and rapid determination of this activity. When maltase is added to the incubation medium (the substrate and reduced glutathione in potassium phosphate buffer, pH 6.8), maintained at 37 degrees C, hydrolysis of the original substrate to p-nitrophenol goes at a constant rate during 4 h. Under optimal conditions of incubation, the Michaelis constant of the reaction, calculated by the Hanes method, was 2.92 +/- 0.84 (SD) X 10(-3) for six different semen samples. Isomaltase appeared to be absent from seminal plasma. The enzyme is stable to freezing and slow thawing and can be stored for at least 26 days at -80 degrees C. Its molecular weight is 259 000. Tris(hydroxymethyl)aminomethane (pH 6.8) exerts a noncompetitive inhibition on the enzyme activity. In 68 men 23 to 45 years old, whose semen analyses were normal, the seminal plasma maltase activity was 467 +/- 135 (SD) mU/g of protein. It was generally decreased in patients with infertility disorders.

145 citations

Journal ArticleDOI
TL;DR: Two NAD-dependent aldehyde dehydrogenase enzymes from rat liver mitochondria have been partially purified and characterized and by utilization of the different substrate properties of these two enzymes it was possible to demonstrate a time-dependent release from digitonin-treated Liver mitochondria.

145 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202214
2021807
20201,053
20191,064
20181,112
20171,024