Hexokinase II of pea seeds

A second hexokinase (EC 2.7.1.1) was obtained from pea seed (Pisum sativum L. var. Progress No. 9) extracts. The enzyme, termed hexokinase II, had a high affinity (Km, 48 micromolar) for glucose and a relatively low affinity (Km, 10 millimolar) for fructose. The Km for MgATP was 86 micromolar. Mg2+...

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Bibliographic Details
Published in:Plant physiology (Bethesda) 1981-11, Vol.68 (5), p.1123-1127
Main Authors: Turner, J F, Copeland, L
Format: Article
Language:English
Subjects:
Aluminum
Citrates
Dehydrogenases
Enzymes
Hexoses
Liver
Monovalent cations
Peas
Phosphorylation
Sugars
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Summary:A second hexokinase (EC 2.7.1.1) was obtained from pea seed (Pisum sativum L. var. Progress No. 9) extracts. The enzyme, termed hexokinase II, had a high affinity (Km, 48 micromolar) for glucose and a relatively low affinity (Km, 10 millimolar) for fructose. The Km for MgATP was 86 micromolar. Mg2+ was required for activity, but excess Mg2+ was inhibitory. MgADP inhibited hexokinase II. The addition of salts of monovalent cations increased hexokinase II activity. Al3+ was a strong inhibitor of the enzyme at pH 6.6 but not at the optimum pH (8.2). Citrate and 3-phosphoglycerate activated pea seed hexokinase II at pH 6.6, probably by coordinating with aluminum present as a contaminant in commercial ATP. The properties of hexokinase II are compared with those of the other three hexose kinases obtained from pea seed extracts. The possible role of these enzymes in plant carbohydrate metabolism is discussed.
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.68.5.1123