|
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 |
Activity |
2.4.1.1 |
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 2.4.1.1) 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 |
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