PMID: 36156Apr 12, 1979

Some properties of starch phosphorylase from cotyledons of germinating seeds of Voandzeia subterranea

Biochimica Et Biophysica Acta
G M Umezurike, S A Ekhorutomwen


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.

Related Concepts

Cations, Divalent
Cyclic AMP, (R)-Isomer
5'-Adenylic Acid
Hydrogen-Ion Concentration
Edetic Acid, Calcium, Sodium Salt

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