Effect of Ammonia Concentration on Activity of Enzymes of Ammonia Assimilation and on Synthesis of Amino Acids by Mixed Rumen Bacteria in Continuous Culture

Abstract

Rumen microorganisms from a cow fed a synthetic diet containing nonprotein nitrogen were maintained in an artificial rumen on a similar diet. Ammonia concentration in the artificial rumen was varied by infusion of different concentrations of ammonium chloride, and activities of enzymes associated with ammonia metabolism and concentration of free amino acids were assayed. Low ammonia concentration caused a ten-fold increase in the specific activity of glutamine synthetase. Activity of asparagine synthetase and aspartate aminotransferase did not respond consistently to ammonia concentration. Specific activities of reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate specific glutamate dehydrogenases were approximately equal when the artificial rumen was inoculated but the latter was predominant by day 4 or 5. Rumen microbial extracts possessed glutamate synthase activity which in conjunction with glutamine and asparagine synthetases may provide an efficient means of glutamate synthesis at low rumen ammonia concentrations. Aspartate and glutamate concentrations did not respond to ammonia concentrations. Alanine and glycine were metabolized readily by rumen microorganisms when the free ammonia concentration was low. When ammonia concentration was high, alanine concentration rose rapidly suggesting that alanine might serve as a storage depot for ammonia and also might provide an additional route for transport of glucose precursors (i.e., pyruvate) from the rumen.