Calmodulin‐dependent multiprotein kinase and protein kinase C phosphorylate the same site on HMG‐CoA reductase as the AMP‐activated protein kinase

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Abstract
Calmodulin‐dependent multiprotein kinase and protein kinase C phosphorylate and inactivate both intact, microsomal HMG‐CoA reductase, and the purified 53 kDa catalytic fragment. Isolation of the single phosphopeptide produced by combined cleavage with cyanogen bromide and Lys‐C proteinase reveals that this is due to phosphorylation of a single serine residue near the C‐terminus, corresponding to serine‐872 in the human enzyme. This is identical with the single serine phosphorylated by the AMP‐activated protein kinase. The nature of the protein kinase responsible for phosphorylation of this site in vivo is discussed.