We have shown previously that vanadate stimulates overall endogenous phosphorylation of proteins in subcellular particulate fractions. In brain mitochondria there is a single peptide band of Mr (approx.) 34 kDa, phosphorylation of which is inhibited rather than stimulated by both vanadate and vanadyl ions. Here, further characterization of this unique effect of vanadium ions is reported. Phosphorylation of the 34 kDa protein proceeds in the Triton X-100 extracts of mitochondria. The P-labeled 34 kDa band was recovered from TCA sediments of endogenously phosphorylated mitochondria. Acid lability of the phosphate linkage suggests a bond of P-N type. Phosphorylation of the 34 kDa protein is highly sensitive to Mg2+, while Mn2+ is a less potent activator. The results provide further evidence for existence of a protein occurring exclusively in mitochondria, the phosphorylation of which is selectively modified by both vanadate anion and vanadyl cation in a way differing from those hitherto described.

Institute of Physiology Czechoslovak Academy of Sciences Prague

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