title: Some properties of starch phosphorylase from cotyledons of germinating seeds of Voandzeia subterranea.
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.
mesh_terms: D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005958:Glucosephosphates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D006005:Phosphorylases / Q000378:metabolism*; D011773:Pyruvates / Q000494:pharmacology; D012639:Seeds / Q000201:enzymology*
chemical_list: D002413:Cations, Divalent; D005958:Glucosephosphates; D011773:Pyruvates; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D000242:Cyclic AMP; D006005:Phosphorylases