5'-AMP INHIBITS DEPHOSPHORYLATION, AS WELL AS PROMOTING PHOSPHORYLATION, OF THE AMP-ACTIVATED PROTEIN-KINASE - STUDIES USING BACTERIALLY EXPRESSED HUMAN PROTEIN PHOSPHATASE-2C-ALPHA AND NATIVE BOVINE PROTEIN PHOSPHATASE-2A(C)

Human protein phosphatase-2C alpha (PP2C alpha) was purified to homoge neity after expression in Escherichia coli, AMP inhibited the dephosph orylation of AMP-activated protein kinase (AMPK), but not phosphocasei n, by PP2C alpha. The concentration dependence and the effects of othe r nucleotides (ATP and formycin A-5'-monophosphate) suggest that AMP a cts by binding to the same site which causes direct allosteric activat ion of AMPK, A similar, although less pronounced, effect was observed with another protein phosphatase (PP2A(C)). We have now shown that AMP K activates the AMPK cascade by four mechanisms, which should make the system exquisitely sensitive to changes in AMP concentration.