Involvement of vitamin B6 in the dethiomethylation of methionine by rumen microorganisms.

The dethiomethylation of methionine by a dialyzed extract obtained from the protozoa-rich fraction of rumen fluid is stimulated 2.5-fold by pyridoxal phosphate and strongly inhibited by deoxypyridoxine, a pyridoxal phosphate antagonist. These effects are not seen with undialyzed extracts or with whole rumen fluid. It is suggested that the anaerobic dethiomethylation of methionine by rumen microorganisms requires pyridoxal phosphate as a cofactor.