Carbamyl Phosphate Synthesis in the Earthworm Lumbricus terrestris

Abstract

The enzymatic synthesis of citrulline from ammonia, bicarbonate, adenosine triphosphate, and L-ornithine takes place in the soluble fraction of gut tissue of the earthworm. The synthesis occurs at low ammonia concentrations, is dependent upon added N-acetyl-L-glutamate, and results in incorporation of the bicarbonate carbon into the ureido group of the citrulline molecule. Carbamyl phosphate is the intermediate in the reaction and its biosynthesis in the earthworm is mediated by a carbamyl phosphate synthetase system similar to that of ureotelic vertebrates.