Keto acids, by oxidation

It thus appears that in animals d-methionine as well as Z-methionine can furnish the corresponding keto acid by oxidative deamination. But it is actually impossible to state there exists a relationship between the similarity in behavior of the two stereoisomers and the similarity of their ability to form sulfate. The fate of sulfur of the a-keto- v-methiobutyric acid is little known as yet according to Waelsch and Borek (140) the acid is broken down in acid or alkaline medium or by boiling to methyl mercaptan and an undetermined residue, and the authors think that this possibly represents a model of a physiological reaction. On the other hand, this same acid seems to be able to take part in the same transmethylation reactions as Z-methionine (58). It is therefore very unlikely that the sulfur of this keto acid can be oxidized directly to sulfate. 

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