Ammonia Metabolism in Rumen Bacteria and Mucosa from Sheep Fed Soy Protein or Urea1

Abstract

Potential pathways of ammonia metabolism in rumen bacteria and rumen mucosa were investigated using enzymatic criteria. Amination and transamination reactions appear to be the major mechanisms for ammonia assimilation by rumen bacteria. Carbamyl phosphokinase was found to play a minor role, but glutamine synthetase may be of substantial importance in utilization of ammonia by rumen bacteria. Extracts of rumen bacteria obtained from urea-fed sheep exhibited lower specific activities of urease, glutamate-oxaloacetate and glutamate-pyruvate transaminases, and glutamate dehydrogenases than comparable preparations from soy protein-fed animals. This may be the result of dietary nitrogen source altering rumen microbial populations or rumen environments, or both. Although activities of enzyme systems which utilize ammonia exceeded those which produce ammonia, the higher rumen ammonia concentration in urea-fed sheep supports the postulate that the rate of ammonia production from urea is greater than the rate of ammonia utilization. Since actual rates of product formation are not controlled by enzyme activities alone, insufficient amounts of substrates, cofactors, energy and cell permeability may be largely responsible for ammonia utilization in the rumen occurring at a lower rate than its production from urea. Transaminases, glutamate dehydrogenases and urease were also present in rumen mucosa.