SUCCINIC ESTER AND AMIDE OF HOMOSERINE: SOME SPONTANEOUS AND ENZYMATIC REACTIONS.

O-Succinylhomoserine and N-succinylhomoserine have been synthesized. The first is rapidly transformed into the second by alkali. In acid, the second undergoes ring closure to the lactone, rather than the reverse acyl transfer. Neither supports the growth of methionine auxotrophs of Neurospora or Salmonella. However, bacterial extracts rapidly catalyze formation of a compound, chromatographically identical with cystathionine, from cysteine and O-succinylhomoserine. In the absence of cysteine the O-succinylhomoserine is converted to alpha-ketobutyrate. Both these reactions are absent from the same Salmonella mutant, and therefore are probably catalyzed by a single enzyme which is needed for methionine synthesis. Both reactions require pyridoxal phosphate. N-succinylhomoserine does not undergo either reaction.