Abstract
Methylene blue-sensitized photooxidation of the cytosolic aspartate aminotransferase from pig heart yielded a preparation which was inactive in the transamination reaction with natural substrates (L-aspartate and a-keto-glutarate) but fully active in the α, β-elimination reaction with β-chloro-Lalanine as well as in the transamination reaction with L-alanine. The inactivation results from photooxidative destruction of a histidyl residue in accord with the result reported by Martinez-Carrion et al. [ J. Biol. Chem. 242, 1426 (1967)]. These results indicates that the histidyl residue does not function as a base abstracting the α-hydrogen atom of these substrates but acts as a catalytic residue involved in the interaction with the distal carboxylate of a natural dicarboxylic substrate as proposed previously [ Morino et al., J. Biol. Chem. 249, 6684 (1974)].
Published Version
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