KINETIC-PROPERTIES OF 2 STARCH PHOSPHORYLASES FROM PEA SEEDS

Both of the starch phosphorylase fractions from Victory Freezer pea seeds, that can be separated by DEAE-cellulose chromatography and purified by Sepharose 4B-starch affinity chromatography, contain pyridoxal 5′-phosphate. The addition of further quantities of pyridoxal 5′-phosphate causes inactivation. Both enzymes showed similar bi-substrate kinetics with d-Glc-1-P and varying amounts of amylopectin and also with Pi and varying amounts of amylopectin. In the direction of glucan sythesis the Km for amylopectin with phosphorylase II was much higher than with phosphorylase I. However, the two enzymes differed in their behaviour on glucan degradation at varying concentrations of Pi. With phosphorylase II the Km for amylopectin was dependent on the concentration of Pi but that for phosphorylase I was constant. Phosphorylase II was strongly inhibited by ADPG in the direction of glucan degradation but only slightly in the direction of glucan synthesis by both ADPG and UDPG. Phosphorylase I was only slightly inhibited by ADPG in both directions and by UDPG in synthesis. UDPG inhibited both enzymes moderately in glucan degradation,. © 1978.