A protein kinase C‐like activity in Escherichia coli

Summary The protein kinase C (PKC) family comprises calcium‐ and phospholipid‐dependent kinases whose activity is stimulated by diacylglycerol and tumour‐promoting phorbol esters such as 12‐tetradecanoyl phorbol‐13‐acetate (TPA). In the Gram‐negative bacterium Escherichia coli, functional similarity to PKC was demonstrated in crude extracts by calcium and phospholipid‐dependent, TPA‐stimulated phosphorylation of a small number of endogenous substrates. Activity was reduced by sphingosine, a known inhibitor of eukaryotic PKC. Structural similarity to PKC was demonstrated in crude and partially purified bacterial extracts by cross‐reactivity with several monoclonal antibodies. This revealed isozyme‐specific homology between a protein(s) of relative molecular mass 80–85000 in E. coli and the α‐and γ‐isozymes, but probably not the β‐isozyme, of eukaryotic PKC.