Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Soluble chloroplast coupling factor 1 (CF1) and the ATP synthase complex, under uncoupled conditions, can form bound ATP from tightly bound ADP and medium Pi. This partial reaction is a powerful probe of the mechanism of ATP synthesis. During our study of the synthesis of bound ATP by CF1 other enzyme activities, which generate [32P]nucleotides from 32Pi, were characterized and controlled. Two enzymes present at significant levels in the preparations are polynucleotide phosphorylase and adenylate kinase. Polynucleotide phosphorylase (PNPase) was found both in thylakoid and CF1 preparations and catalyzed the formation of [beta-32P]ADP via its Pi----ADP exchange activity. The formation of [beta-32P]ADP during net photophosphorylation is attributable to adenylate kinase action on the [32P]ATP formed since hexokinase and glucose effectively block its production. In addition, PNPase also degraded RNA present in thylakoid preparations yielding all four [32P]nucleoside diphosphates. PNPase was also shown to catalyze a Pi----ATP exchange that is dependent on RNA primers and other cofactors.
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PMID:Enzymatic activities in thylakoid membranes, which form medium [32P]NDP and [32P]ATP from 32Pi. Polynucleotide phosphorylase and adenylate kinase. 609 Jan 33

Polynucleotide phosphorylase (PNPase) is a prokaryotic enzyme that catalyzes phosphorolysis of polynucleotides with release of NDPs. It is also believed to play a key role in turnover of prokaryotic transcripts, thus regulating gene expression. At the moment, only radioisotopic methods are available for assaying PNPase in crude extracts; these involve incubating [32P]phosphate and poly(A) in the presence of the enzyme, separating [32P]phosphate from [32P]ADP, and quantifying ADP by scintillation counting. Photometric assay using pyruvate kinase and lactate dehydrogenase as auxiliary enzymes is not feasible in crude extracts because of endogenous ATPase activities, which regenerate ADP from the ATP released by pyruvate kinase. Here, we present a simple photometric assay that uses a cyclic detection system which, due to the sequential action of pyruvate kinase and hexokinase, results in an exponential increase of ADP and glucose 6-phosphate. Glucose 6-phosphate is then revealed by a glucose-6-phosphate dehydrogenase reaction. Based on the theoretical model, a linear increase in absorbance is predicted as a function of the square of the reaction time, with a slope proportional to PNPase activity. Experimental data confirmed the theoretical predictions and showed that the assay was quantitative and unquestionably specific. We also devised a simple procedure for determining absolute enzyme activities (expressed in micromoles of product formed per minute) using exact amounts of pure PNPase as internal standards.
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PMID:Photometric assay for polynucleotide phosphorylase. 1022 10