Evidence for a new, high-molecular weight isoform of protein kinase C in rat hippocampus

We describe a new form of protein kinase C (PKC) with a molecular weight of 97 kDa, higher than the known forms of vertebrate PKC. This putative new high-molecular weight isoform, which we are calling PKC(HMW), is increased in the membrane fraction either upon application of phorbol esters or with afferent synaptic stimulation of Schaffer collaterals in hippocampal slices. The protein cross-reacts on immunoblot with affinity-purified polyclonal antiserum raised against a peptide derived from the carboxy-terminus of PKCη; it does not cross-react, however, with antiserum against the amino-terminal region of PKCη. In the tissues examined, PKC(HMW) is localized primarily in brain, in contrast to PKCη, which is found predominantly in lung and skin.