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

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Abstract
Rumen microorganisms from a cow fed a synthetic diet containing nonprotein nitrogen were maintained in an artificial rumen on a similar diet. NH3 concentration in the artificial rumen was varied by infusion of different concentrations of NH4Cl, and activities of enzymes associated with NH3 metabolism and concentration of free amino acids were assayed. Low NH3 concentration caused a 10-fold increase in the specific activity of glutamine synthetase [EC 6.3.1.2]. Activity of asparagine synthetase [EC 6.3.1.1] and aspartate aminotransferase [EC 2.6.1.1] did not respond consistently to NH3 concentration. Specific activities of NADH and NADPH specific glutamate dehydrogenases [EC 1.4.1.2 and EC 1.4.1.4, respectively] 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 [EC 2.6.1.53] activity which in conjunction with glutamine and asparagine synthetases may provide an efficient means of glutamate synthesis at low rumen NH3 concentrations. Aspartate and glutamate concentrations did not respond to NH3 concentrations. Alanine and glycine were metabolized readily by rumen microorganisms when the free NH3 concentration was low. When NH3 concentration was high, alanine concentration rose rapidly suggesting that alanine might serve as a storage depot for NH3 and also might provide an additional route for transport of glucose precursors (i.e., pyruvate) from the rumen.