Chemical Inhibition of Amino Acid Deamination by Ruminal Microbes in Vitro2

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Abstract
Effects of various chemical inhibitors of amino acid deamination were tested in a batch-type ruminal in vitro system. Casein hydrolysate was added to the medium at about 3.4 mM total amino acids. Initial experiments comparing toluene, thymol, penicillin G, oxytetracycline, chlortetracycline and hydrazine showed that the highest recoveries (P<.05) of total amino acids were obtained with hydrazine (97%) and thymol (109%). Further studies were made comparing hydrazine with various hydrazine derivatives, other carbonyl reagents and vitamin B6 inhibitors and sodium arsenite, an inhibitor of Stickland-type amino acid deamination. Although none reduced deamination more than hydrazine, phenylhydrazine, p-nitro-phenylhydrazine, methylhydrazine and sodium arsenite gave amino acid protection equal to hydrazine (P<.05). Amino acid protection by p-hydrazinobenzoic acid, potassium cyanide and (aminooxy) acetic acid was intermediate between hydrazine and control (P<.05). Amino acid protection by thiosemicarbazide, p-hydra-zinobenzenesulfonic acid and iproniazid was not different from control (P>.05). Hydrazine was then compared with diphenyliodonium chloride (DIC) at various concentrations. Total amino acid recoveries at .05 mM DIC were comparable to 5.0 mM hydrazine. Recoveries of individual amino acids generally followed the trends observed for total amino acids, but with some notable exceptions. Recoveries of aspartic and glutamic acids at even the highest hydrazine concentrations were low (40 to 60%). Arginine recovery was near zero in all hydrazine and DIC incubations. Recoveries of several amino acids (isoleucine, leucine, valine, lysine and tyrosine) were substantially greater than 100% in the presence of either hydrazine or DIC. Both compounds equally inhibited microbial ammonia uptake and hence would be expected to inhibit microbial growth. Hydrazine and particularly DIC inhibited in vitro casein degradation. The results indicate that carbonyl reagents, which act presumably by inhibiting vitamin B6, may be potentially useful for reducing ruminal amino acid deamination. DIC, which appears to inhibit deamination by another mechanism, is effective at very low ruminal concentrations and may be a useful feed additive. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.