Immunological cross-reactivity between carbamyl phosphate synthetases I, II, and III.

Four types of carbamyl phosphate synthetase have been previously distinguished on the basis of catalytic properties and metabolic role. Immunoblot assay has now demonstrated cross-reactivity between rat liver carbamyl phosphate synthetase I and the following other three types of synthetases: carbamyl phosphate synthetase II from SV40-transformed baby hamster kidney cells, carbamyl phosphate synthetase III from spiny dogfish liver and from largemouth bass liver, and Escherichia coli carbamyl phosphate synthetase. The strongest cross-reactivity was observed between carbamyl phosphate synthetases I and III. These findings indicate at least partial structural homology among the various synthetases and constitute the first demonstration of such a relationship among the enzymes.