EFFECTS OF DIPHENYLIODONIUM CHLORIDE ON PROTEOLYSIS AND LEUCINE METABOLISM BY RUMEN MICROORGANISMS

Diphenyliodonium chloride (DIC) at 0.3 and 0.8 mM inhibited hydrolysis of casein by a rumen microbial ecosystem unadapted to DIC by as much as 30%. Adaptive effects to DIC on leucine oxidation over 37 days were evaluated in a batch culture system repetitively diluted with culture media devoid of protein but containing carbon and nitrogen sources es sential for growth DIC concentrations up to 0.1 mM had no effect on co ncentrations of microbial protein during the 37 day period of semi-con tinuous culture. Concentrations of ammonia were depressed (P less than or equal to 0.05) by day 5 after initiating an influx of 0.1 mM DIC w hile other levels of DIC were without effect. Effects of DIC on oxidat ion of leucine were determined in aliquots of removed culture to which [1-C-14]-leucine was added, Leucine oxidation was assessed as the (CO 2)-C-14 evolved during a 1 h fermentation with [1-C-14]-leucine and su bsequent peroxide oxidation of the residual [1-C-14]-alpha-ketoisocapo rate (KIC). The proportion of (CO2)-C-14 recovered during fermentation and from KIC was essentially equal (regression coefficient of 1.0244 +/- 0.04) and did not differ (P > 0.05) due to level of DIC or days of culture. The results suggests that leucine was deaminated via oxidati ve deamination to KIC followed by oxidative decarboxylation of KIC to isovalerate. These results illustrate that DIC can completely inhibit leucine degradation without detrimental effects on microbial growth in culture systems derived from rumen fluid that are allowed to adapt to DIC. (C) 1997 Elsevier Science B.V.