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B6db references: 79187983

type Journal Article
authors Umezurike, G. M.; Ekhorutomwen, S. A.
title Some properties of starch phosphorylase from cotyledons of germinating seeds of Voandzeia subterranea
journal Biochim Biophys Acta
ui 79187983
year (1979)
volume 567
number 2
pages 331-8.
keywords Adenosine Monophosphate/pharmacology
abstract Two isoenzymes (Forms I and II) of starch phosphorylase (1,4-alpha-D- glucan: orthophosphate alpha-glucosyltransferase, EC were found in cotyledons of germinating seeds of Voandzeia subterranea L. Thouars. Phosphorylase I, which was the major component, had a pH optimum of 5.5--5.6, whereas phosphorylase II had a pH optimum of 6.1-- 6.3. Phosphorylase I had a molecular weight of 204 000 +/- 4000 and a subunit molecular weight of about 95 000. Phosphorylase I was stimulated by Mg2+, Mn2+, AMP, cyclic AMP, pyruvate and EDTA, but inhibited by Fe2+, Cu2+, Zn2+ and ATP. Stimulation of phosphorulase I by AMP was accompanied by changes in the affinity of the enzyme for glucose-1-phosphate in the presence of increasing AMP concentrations, and of AMP in the presence of increasing glucose-1-phosphate concentrations. Double-reciprocal plots of initial velocity data were non-linear (convex up) at low glucose-1-phosphate concentrations but became linear in the presence of AMP or ATP. Double-reciprocal plots were linear at high glucose-1-phosphate concentrations in the absence or presence of modifiers.
last changed 2002/11/12 16:17

B6db references