[Glycogen phosphorylase activity of full term immature human placentas].

Human placenta contains glycogen phosphorylase activity (E.C. 2.4.1.1) in two interconvertible forms, one is already active and the other is actibatable by 5' AMP. The human placenta contains also a sufficient amount of endogenous phosphorylase b kinase and phosphorylase a phosphatase, to allow this interconversion. The phosphorylase activity is higher in immature placentas than in full-term organs, as in the latter the inactive phosphorylase is only partially revealed by 5' AMP as in other steroidogenic organs. By contrast, in immature placentas the inactive glycogen phosphorylase is completely revealed by this nucleotide.