Histones H3 and H4 inhibit protein kinase C specifically

Early effects of TPA on protein kinase activity in murine thymocytes. Reduction of protein kinase C activity in the cytosol and increase of Ca2+ and phospholipid-independent kinase activity in the particulate fractions

Brief treatment of intact thymocytes with TPA and other tumor promoters causes a reduction in protein kinase C activity from the cytosol and an increase in kinase activity in the particulate fraction. In contrast to the activity in the cytosol, which is absolutely dependent on the addition of Ca2+, phosphatidylserine and diolein, the activity in the particulate fraction is independent of these agents. Analysis of target specificity of the particulate kinase activity using exogenous and endogenous substrates suggests that the increased phosphorylation in the particulate fraction is catalysed by protein kinase C with altered catalytic properties. Although interleukin-1 and TPA are both co-mitogens for murine thymocytes, interleukin-1 does not share with TPA its property to alter protein kinase activity in the cytosolic and particulate fractions.

Protein kinase C: rapid enzyme purification and substrate-dependence of the diacylglycerol effect

Protein kinase C has been purified by a rapid method resulting in a high-yield, stable enzyme preparation. The catalytic and regulatory properties of this enzyme preparation were characterized employing histone H1 and HMG8, a proteolytic fragment of H1. The enzyme had a lower Km for HMG8, and was stimulated more effectively by diacylglycerol and phorbol esters in the presence of this substrate. Furthermore, these activators markedly increased the Km for HMG8 but not for H1. Protein kinase C and cyclic AMP-dependent protein kinase phosphorylate serine residues which are located in different, single tryptic peptides from HMG8.