Effect of propionic acid on urea synthesis by sheep liver

Propionate reduced substantially the rate of ureagenesis by slices of sheep liver whereas butyrate did not inhibit urea synthesis. The site of inhibition of urea synthesis by propionate occurs at some point between the fixation of ammonia and the formation of citrulline since 0.5 mM propionate inhibited by 80 per cent the synthesis of citrulline by mitochondria isolated from sheep liver. Since the apparent Ki for propionate is approximately 1.7 mM, the inhibitory effect of propionate on urea synthesis could be of physiological significance in sheep.