ATP‐citrate lyase is another enzyme the histidine phosphorylation of which is inhibited by vanadate

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Abstract
We have recently shown that phosphorylation of histidine residue of the α‐subunit of the succinyl‐CoA synthetase is inhibited by both vanadate and vanadyl. To assess the universality of this inhibition, we have estimated the effect of vanadate on the phosphorylation of another enzyme ATP‐citrate lyase, prepared from rat liver. This enzyme contains histidine as the only amino acid with an acid‐labile (P—N) phosphate bond. The 67% inhibition of endogenous phosphorylation by 1 mM vanadate disappeared after cleavage of the acidic P—N bond of histidine with acidic sample solution. The remaining 33 per cent radioactivity was due to labelling of the acid‐stable phosphoamino acids (P‐serine and P‐threonine), the phosphorylation of which was not affected by vanadate. The dose—response curve for vanadate inhibition closely resembles that shown previously for inhibition of phosphorylation of histidine in the succinyl‐CoA synthetase. The results suggest that the action of vanadate on histidinyl phosphorylation is a more general effect (like its influence on phosphorylation of the protein‐bound tyrosine).