抄録
The apparent Km values of yeast α-glucan phosphorylase [EC 2.4.1.1] for glucose 1-phosphate, glycogen and maltopentaose were 1.3mM, 0.10mM and 8.8mM, respectively. The Km values for maltopentaose clearly distinguished the muscle and yeast enzymes from the potato enzyme. Comparison of the Km values for maltooligosaccharides in the directions of both glycogen synthesis and degradation showed the similarity of the muscle and yeast enzymes. Affinity-gel electrophoresis indicated that the dissociation constant of the yeast enzyme for maltoheptaose was 0.23mM, which was 26-fold smaller than the Km value for maltoheptaose (5.9mM). Inhibition of the yeast enzyme activity by glucose 6-phosphate and UDP-glucose was much stronger than that by fructose 6-phosphate and fructose 1, 6-bisphosphate. Moreover, tryptic inactivation of the yeast enzyme was greatly increased by UDP-glucose and glucose 6-phosphate. Based on the kinetic properties, a regulatory mechanism of the yeast phosphorylase was discussed in comparison with those for the muscle and potato phosphorylases.
