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Metabolic Pathway of Biuret Degradation and Formation of a Biuret-Complex in the Rumen¹

University of Illinois at Urbana-Champaign,³ Urbana 61801

Abstract

The pathway for degradation of biuret in the rumen was studied. Addition of the urease inhibitor, acetohydroxamic acid (AHA), to rumen fluid incubated with biuret, resulted in increased final concentrations of urea and lowered final concentrations of ammonia. The addition of AHA, however, did not decrease the disappearance of biuret. Accumulation of carbon from biuret in urea was monitored using radioactive biuret with or without added urease inhibitor. Subsequent addition of an excess of urease resulted in the release of more ¹⁴CO₂. Results suggest that urease participates in total degradation of biuret in the rumen and that urea is one intermediate compound. A pathway for complete degradation of biuret in the rumen is suggested. Nondegradative disappearance of assayable biuret in the rumen fluid was also studied. Virtually all of the carbon from ¹⁴C-biuret (99.4%) recovered from rumen fluid was found to be present in the soluble fraction. Yet, chemical recovery of biuret from rumen fluid averages only 60 to 80%. Biuret thus appears to be forming a complex with some soluble component(s) of rumen fluid. EDTA addition to rumen fluid prior to the addition of biuret did not reduce the apparent loss of biuret from the rumen fluid, suggesting that mineral complexes are not responsible. Incubation of biuret in a trace mineral salt solution as well resulted in a loss of only 1% of the added biuret. Silicic acid did not complex with biuret. Treatment of rumen fluid containing added biuret with concentrated HCl resulted in release of nonassayable biuret. Biuret complexed with dialyzed rumen fluid, in similar amounts as with nondialyzed rumen fluid, suggesting that large molecular weight compounds are involved. The complexed biuret was also retained during dialysis. It is speculated that formation of a relatively stable protein biuret-complex in rumen fluid is responsible for initial disappearance of biuret during incubation.

¹ Supported in part by: Hatch Grant 20-346, trust funds from Moorman Mfg. Co., Quincy, Ill., and Dow Chemical Co., Midland, Mich.

² Present address: Department of Urology, Medical Hospital, University of Washington, Seattle, Wash. 98105.

³ Department of Animal Science.