The Enzymatic Characteristics and the Control of Glycogen Phosphorylase during Early Amphibian Development

Abstract

Abstract Glycogen phosphorylase has been studied in Rana pipiens eggs and embryos with regard to the nature of the enzyme, its control possibilites, and its involvement in preneurula development. On the basis of enzyme activity, immunological, and electrophoretic comparisons, R. pipiens egg phosphorylase is not wholly identical with the phosphorylases characteristic of skeletal muscle, liver, or kidney tissues. The possibility exists that the egg activity consists of a mixture of types or is a single type peculiar to the embryo. Amphibian egg phosphorylase possesses the same control possibilities as adult tissue forms. It can be activated by AMP. It appears to exist in active and inactive forms, the interconversion of which is catalyzed by endogenous factors having properties of a phosphorylase kinase and phosphorylase phosphatase. The egg phosphorylase kinase is capable of activating purified frog and rabbit muscle phosphorylase, and the purified rabbit muscle phosphorylase b kinase can activate the egg and frog muscle enzymes. However, the egg and rabbit muscle phosphatases are species specific. If the activity of the activated form of egg phosphorylase in the presence of AMP is assigned a value of 100%, its activity in the absence of AMP is 96%. The activity of the inactivated form in the presence of AMP is 35%. In the absence of AMP, the inactivated form has no activity. Phosphorylase in unfertilized R. pipiens eggs is mostly in the inactive form. Shortly after fertilization and at gastrulation, increases in activity and in the -AMP:+AMP activity ratio occur. A cyclic adenosine 3' ,5'-monophosphate-mediated control mechanism is possible as a cyclic AMP-activated protein kinase has been detected in the fractionated egg supernatant. This enzyme mimics the behavior of rabbit muscle phosphorylase kinase kinase.