Propionic and methylmalonic acids inhibit the in vitro phosphorylation of a 85 kDa cytoskeletal protein from cerebral cortex of rats.

In this study we examine the action of methylmalonic (MMA) and propionic (PA) acids, metabolites which accumulate in methylmalonic and propionic acidemias respectively, on the endogenous phosphorylating system associated with the cytoskeletal fraction of cerebral cortex of young rats. Chronic treatment with PA and treatment of tissue slices with MMA or PA are effective in decreasing the in vitro phosphorylation into a 85 kDa cytoskeletal associated protein. We tested the effect of the acids on the endogenous kinase activities by using specific kinase activators and inhibitors. Results demonstrated that the acids interfere with the endogenous cAMP-dependent and Ca2+/calmodulin-dependent kinase activities. Furthermore, in vitro dephosphorylation of the 85 kDa protein was totally inhibited in brain slices treated with the acids. Considering the importance of protein phosphorylation to cellular function, we speculate that alteration in the phosphorylating level of cytoskeletal associated phosphoproteins induced by MMA and PA treatments may somehow be involved in steps leading to brain damage.