title: Inhibition of potato starch phosphorylase by alpha-D-glucopyranose-1,2-cyclic phosphate.
abstract: alpha-D-Glucopyranose-1.2-cyclic phosphate is a potent inhibitor of potato starch phosphorylase-catalyzed (1,4-alpha-D-glucan:orthophosphate alpha-glucosyltransferase, EC 2.4.1.1) starch elongation. The inhibition is competitive with respect to alpha-D-glucopyranose 1-phosphate (Glc-1-P) with Ki approximately 0.07 mM at pH 6.3 and 30 degrees C in 25 mM citrate buffer. The affinity of the phosphorylase - starch complex for the cyclic ester is therefore nearly 30 times as large as for Glc-1-P. Under conditions where alpha-D-glucopyranose-1,2-cyclic phosphate slows starch elongation by a factor of 3, UDPglucose, ADPglucose, D-glucose 6-phosphate, and D-glucose 2-phosphate cause rate reductions of less than 10%. The origin of the relatively strong binding of the cyclic ester to the phosphorylase, and its possible biological significance are discussed.
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D005958:Glucosephosphates / Q000494:pharmacology*; D007700:Kinetics; D006005:Phosphorylases / Q000037:antagonists & inhibitors*; D010944:Plants / Q000201:enzymology*; D013816:Thermodynamics; D014532:Uridine Diphosphate Glucose / Q000494:pharmacology
chemical_list: D005958:Glucosephosphates; D000245:Adenosine Diphosphate Glucose; C015239:glucopyranose-1,2-cyclic phosphate; D006005:Phosphorylases; D014532:Uridine Diphosphate Glucose