Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.21 (beta-glucosidase)
 3,280 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Myrosinase (thioglucoside glucohydrolase; EC 3.2.3.1) is a plant enzyme that hydrolyses glucosinolates, principally to isothiocyanates. Myrosinase was purified to homogeneity in good yield from 8-day-old seedlings of Raphanus sativus (daikon) using a four-step procedure involving chromatographies on anion exchange, hydrophobic Phenyl-Sepharose, gel filtration and concanavalin A-Sepharose. In order to stabilize the enzyme and to avoid excessive peak broadening during chromatography, 30% (v/v) glycerol was added to dialysis and chromatography buffers. The purified enzyme was eluted as a single peak from a gel-filtration sizing column with an apparent molecular mass of 120 kDa. The enzyme was resolved into two subunits with molecular masses of 61 and 62 kDa by SDS/PAGE. Ascorbic acid activated the purified enzyme more than 100-fold. The V(max) and K(m) values for the hydrolysis of allyl glucosinolate (sinigrin) were 2.06 micromol/min per mg of protein and 23 microM in the absence of ascorbate and 280 micromol/min per mg of protein and 250 microM in the presence of 500 microM ascorbate, respectively. As the ascorbate concentration was increased from 50 to 500 microM, the V(max) and K(m) values increased in parallel, and thus the V(max)/K(m) ratio remained constant. Similarly, raising the concentrations of sinigrin increased the concentration of ascorbic acid required for half-maximal activation (K(a)). At a sinigrin concentration of 250 microM, the K(a) for ascorbic acid was 55 microM. Sulphate, a reaction product, was a competitive inhibitor of activity, having a K(i) of 60 mM with respect to sinigrin and of 27 mM with respect to ascorbate. Thus activation of myrosinase from R. sativus by ascorbic acid exemplifies an unusual and possibly unique example of linear 'uncompetitive activation' (i.e. a proportionate increase in V(max) and K(m)) of an enzyme. The enzyme also had beta-glucosidase activity and hydrolysed p-nitrophenyl-beta-d-glucopyranoside.
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PMID:An unusual case of 'uncompetitive activation' by ascorbic acid: purification and kinetic properties of a myrosinase from Raphanus sativus seedlings. 1041 37

Screening for novel thioglucoside hydrolase activity resulted in the isolation of Sphingobacterium sp. strain OTG1 from enrichment cultures containing octylthioglucoside (OTG). OTG was hydrolysed into octanethiol and glucose by cell free extracts. Besides thioglucoside hydrolysis, several other glucoside hydrolase activities were detected in the Sphingobacterium sp. strain OTG1 cell free extract. By adding beta-glucosidase inhibitors it was possible to discriminate between these different activities. Ascorbic acid and D-gluconic acid lactone inhibited the hydrolysis of p-nitrophenyl beta-glucoside, but did not affect octyl- and octylthioglucoside hydrolase activity. Besides OTG, various other thioglucosides were hydrolysed by the novel thioglucosidase, with almost the same activities regardless of the nature of the aglycone, including the myrosinase model substrate sinigrin (a glucosinolate). Sinigrin could also be used as a growth substrate by Sphingobacterium sp. strain OTG1, although at concentrations exceeding 0.15 mM degradation was not complete.
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PMID:Thioglucosidase activity from Sphingobacterium sp. strain OTG1. 1160 17