Topic
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.
Papers published on a yearly basis
Papers
More filters
TL;DR: A comparison of the enzyme activities on various glycosidic substrates indicated that HGT-BG is a broad-specificity type of fungal β-glucosidase, which is of great potential interest in wine and fruit juice processing because it releases aromatic compounds from flavorless glucosidic precursors.
Abstract: Aspergillus oryzae was found to secrete two distinct beta-glucosidases when it was grown in liquid culture on various substrates. The major form had a molecular mass of 130 kDa and was highly inhibited by glucose. The minor form, which was induced most effectively on quercetin (3,3',4',5,7-pentahydroxyflavone)-rich medium, represented no more than 18% of total beta-glucosidase activity but exhibited a high tolerance to glucose inhibition. This highly glucose-tolerant beta-glucosidase (designated HGT-BG) was purified to homogeneity by ammonium sulfate precipitation, gel filtration, and anion-exchange chromatography. HGT-BG is a monomeric protein with an apparent molecular mass of 43 kDa and a pI of 4.2 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing polyacrylamide gel electrophoresis, respectively. Using p-nitrophenyl-beta-D-glucoside as the substrate, we found that the enzyme was optimally active at 50 degreesC and pH 5.0 and had a specific activity of 1,066 micromol min-1 mg of protein-1 and a Km of 0.55 mM under these conditions. The enzyme is particularly resistant to inhibition by glucose (Ki, 1. 36 M) or glucono-delta-lactone (Ki, 12.5 mM), another powerful beta-glucosidase inhibitor present in wine. A comparison of the enzyme activities on various glycosidic substrates indicated that HGT-BG is a broad-specificity type of fungal beta-glucosidase. It exhibits exoglucanase activity and hydrolyzes (1-->3)- and (1-->6)-beta-glucosidic linkages most effectively. This enzyme was able to release flavor compounds, such as geraniol, nerol, and linalol, from the corresponding monoterpenyl-beta-D-glucosides in a grape must (pH 2.9, 90 g of glucose liter-1). Other flavor precursors (benzyl- and 2-phenylethyl-beta-D-glucosides) and prunin (4',5,7-trihydroxyflavanone-7-glucoside), which contribute to the bitterness of citrus juices, are also substrates of the enzyme. Thus, this novel beta-glucosidase is of great potential interest in wine and fruit juice processing because it releases aromatic compounds from flavorless glucosidic precursors.
321 citations
TL;DR: Consistent with the subcellular localization of most proteins bearing O-GlcNAc, the activity appears to reside in the cytosolic portion of the cell when compared to two lumenal marker enzymes, galactosyltransferase and mannose-6-phosphatase.
321 citations
TL;DR: It is proposed that the conformational flexibility of aromatic residues generates a plasticity in the active center that contributes to the high efficiency of AChE and its ability to respond to external stimuli.
319 citations
TL;DR: The effects of hydrogen-ion concentration on enzyme activity are consistent with the view that unprotonated amines are the species which bind to the enzyme, and led to formulation of a proposed mechanism of dehydrogenation which does not depend upon intermediate formation of Schiff base from the substrate amine.
318 citations
TL;DR: Gly-Pro β-naphthylamide or Gly-Pro-Leu was a competitive inhibitor with each X-Pro p-nitroanilide as substrate, which had the highest activity among the substrates at pH 8.7, followed by p-NitroAnilides of Ala, Lys, Arg, Glu, and Asp in a decreasing order of activity.
315 citations