Stability of Methionine Hydroxy Analog in Rumen Fluid and Its Conversion in Vitro to Methionine by Calf Liver and Kidney

In vitro rumen studies with methionine hydroxy analog-1-14C (M-analog) and L-methionine-1-14C indicate that the analog is much more resistant to rumen microbial degradation. The disappearance of 14C-methionine was associated with the formation of large amounts of 14CO2 and increase in 14C-activity of the rumen solids, the latter being indicative of incorporation of methionine or its metabolites or both into bacterial cellular components. The disappearance of 14C-M-analog, in contrast, was associated with 14CO2 formation but not with bacterial cell incorporation. Incubation of 14C-M-analog with calf liver and kidney microsomal fractions revealed that these enzyme systems were equally capable of converting the analog to methionine. Glutamine, leucine, and asparagine were comparable as amino group donors.