Molecular cloning has provided evidence for a new family of protein kinases in eukaryotic
cells. These kinases show no sequence similarity with other eukaryotic protein kinases, but
are related by sequence to the histidine protein kinases found in prokaryotes. These protein
kinases, responsible for phosphorylation and inactivation of the branched-chain α-ketoacid
dehydrogenase and pyruvate dehydrogenase complexes, are located exclusively in
mitochondrial matrix space and have most likely evolved from genes originally present in …