pp60c-src kinase expression in brain of adult rats in relation to age.

Although there is evidence of alterations in brain protein phosphorylation patterns with age, it is not known if the protein kinases that phosphorylate only at tyrosine residues are involved in these changes. For this reason, we examined the age-related expression of pp60c-src, a tyrosine protein kinase enriched in neural tissues, in whole brain of adult Fischer-344 rats. The pp60c-src kinase activity was immunoprecipitated using a monoclonal antibody and the incorporation of [32P] from radiolabeled ATP into an exogenous substrate (casein) measured. The results showed that there was a substantial amount of pp60c-src kinase activity in brain of the adult animals ranging in age from 4 to 23 months and that it was not significantly different among these groups. Also, immunoprecipitates obtained under conditions of monoclonal antibody excess and utilized for immunoblot analysis indicated that the relative levels of the pp60c-src protein were unchanged in the same animals. These results suggest that, at the whole brain level, the pp60c-src kinase has a stable turnover and that a high amount of activity is biologically important in brain of adult rats through early senescence.