Abstract
Affinity purification of two phosphorylases from pea cotyledons has been achieved by chromatography on amylopectin bound to Concanavalin A—Sepharose. Cytoplasmic enzyme bound to amylopectin from normal-starch but the plastid enzyme required the amylopectin from high-amylose starch, with a longer average chain length. The V max/ K m values for a series of branched α-glucans with differing average chain lengths were linearly related to average external chain length. Rabbit-muscle phosphorylase limit-dextrin competitively inhibited the cytoplasmic enzyme with a K is of 13 μM non-reducing end-groups. Progress curves of phosphorolysis with both enzymes showed no product inhibition by d-glucose α-1-phosphate. A study of molecular models of the two reactions suggests that separate binding patterns of glucan may not be necessary for phosphorolysis and synthesis.
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