Activation of Muscular Phosphorylase b Kinase by a Minute Amount of Ca Ion

Open Access
Publisher Website
Google Scholar
Abstract
Phosphorylase b kinase [EC 2.7.1.38] from rabbit skeletal muscle required Ca ion for its activity. Little activity was shown in the presence of Ca ion less than 10−10M. A significant activity, about 5% of the maximum, was observed at 5×10−8M Ca ion. The concentrations of Ca ion which gave the half maximum activity and the maximun activity of the purified enzyme were about 10−5M and 4×10−4M, respectively. Phosphorylase b kinase from rabbit cardiac muscle and chicken gizzard smooth muscle showed essentially the same responses to Ca ion as those of skeletal one. One gram of rabbit skeletal muscle contained 9,160 units of phosphorylase [EC 2.4. 1.1] and that amount of phosphorylase b kinase which could yield 1,490 units of phosphorylase a per second from phosphorylase b in the presence of 4×10−5M Ca ion. This indicates that the kinase in rabbit skeletal muscle can convert phosphorylase b to phosphorylase a within 6.1 sec. This value is compatible with the reported value needed for the conversion of phosphorylase b to phosphorylase a during the tetanus of frog skeletal muscle. The stimulating effect of cyclic AMP on the kinase also required a minute amount of Ca ion. The activation process of the kinase by a minute amount of Ca ion was reversible, either in the presence or absence of cyclic AMP. The physiological significance of Ca ion as a triggering agent of glycogenolytic process was discussed with particular references to the role of Ca ion in excitation-contraction coupling.

This publication has 0 references indexed in Scilit: