Bovine glutamate dehydrogenase. Loss of allosteric inhibition by guanosine triphosphate and nitration of tyrosine-412.

Bovine liver glutamate dehydrogenase is desensitized to its allosteric inhibitor guanosine triphosphate upon reaction with tetranitromethane. The presence of GTP affords at most only a small protection against loss of the inhibitory effect of GTP. By amino acid analysis, the nitration of tyrosine appears to be the major change in the protein upon reaction with tetranitromethane and the modification most likely to be responsible for the loss of GTP inhibition. The rate of formation of 3-nitrotyrosine during the reaction of the enzyme with tetranitromethane is apparently the sum of two concurrent reactions, an initial rapid reaction which accounts for the nitration of approximately 1 tyrosyl residue per subunit chain and a slower reaction which also accounts for significant tyrosine nitration. We have identified the tyrosyl residue which is rapidly nitrated by the isolation of a single labeled peptide from a tryptic digest and by the isolation of a labeled cyanogen bromide peptide. In both cases, the modified residue proved to be tyrosine-412 according to the present tentative numbering of the polypeptide chain.