Assessment of protein kinase C isozymes by two-site enzyme immunoassay in human brains and changes in Alzheimer's disease

Abstract

We assessed the amount of protein kinase C (PKC) in samples from postmortem normal human and Alzheimer's disease (AD) brains by a two-site enzyme immunoassay that quantitatively identified types α, β, and γ isozymes. In the normal human brain matter, type β was the main type present, the majority of each isozyme of PKC being present in the membranous fraction of the brain tissues. In AD brains, the amount of type β PKC was significantly reduced in the membranous fraction of the temporal cortical tissues. The amounts of types α and γ in the membranous fraction and types α, β, and γ in the cytosolic fraction in AD brains were lower than in the control brains, but the difference was not significant. There was also a significant decrease in the levels of PKC in the membranous fraction of AD brains, as measured by radioactive phorbol ester binding. These results suggest that the type β PKC isozyme is mainly present in the human temporal cortex and that reduced levels of type β PKC in the membranous fraction may reflect a biochemical deficit related specifically to the pathogenesis of AD.