Activities of Enzymes Related to NADPH Generation and Amino Acid Metabolism in the Ruminal Mucosa of Sheep

Abstract

Experiments were performed with growing lambs to investigate dietary influences on enzymes involved in the metabolism of propionate, amino acids and NADPH in the ruminal mucosa. Glutamate dehydrogenase (GDH) was the only enzyme assayed that was consistently affected by diet. First, lambs were fed either rolled barley, resulting in epithelial hyperkeratosis, or whole unprocessed barley, resulting in keratin aplasia and reduced GDH activity. Secondly, lambs were fed isonitrogenous diets containing either fish meal or urea. GDH activity was greater when fish meal was fed. NADP-isocitrate dehydrogenase was more active than other NADPH-generating enzymes in ruminal mucosa and several other lamb tissues, but the operation of the isocitrate cycle in rumen epithelium may be restricted by a low activity of aconitate hydratase. These results suggest that enzyme activities in ruminal mucosa are generally unresponsive to diet and that adaptations in GDH are related to changes in rumen morphology, rather than to isocitrate cycle activity or ammonia assimilation.