Alpha-ketoisocaproate increases the in vitro 32P incorporation into intermediate filaments in cerebral cortex of rats.

In this study we investigated the effects of alpha-ketoisocaproic (KIC), alpha-ketoisovaleric (KIV) and alpha-keto-beta-methylvaleric (KMV) acids on the phosphorylation of intermediate filament (IF) proteins of cerebral cortex of rats. Tissue slices were incubated with [32P] orthophosphate in the presence or absence of the acids. The intermediate filament enriched cytoskeletal fraction was isolated and the radioactivity incorporated into neurofilament subunits, vimentin and glial fibrillary acidic protein was measured. Results demonstrated that KIC significantly increased phosphorylation of these proteins whereas the other acids had no effect. Experiments using protein kinase inhibitors indicated that the effect of KIC was mediated by Ca2+/calmodulin- and cAMP-dependent protein kinases. This study provides evidence that KIC, a key metabolite accumulating in maple syrup urine disease, increases phosphorylation of IF proteins.