Identification of an isoform of ornithine carbamoyltransferase that can effectively utilize canaline as a substrate from the leaves of Canavalia lineata.

An isoform of ornithine carbamoyltransferase that can utilize effectively canaline as a substrate (C-OCT) was identified from the leaves of Canavalia lineata (Thunb.) DC. The molecular mass of native C-OCT was 109 kDa by Sephacryl S-200 gel filtration and that of the subunit was 36 kDa by SDS-PAGE and immunoblotting using the antibody against kidney bean ornithine carbamoyltransferase (OCT). C-OCT has pH optimum at 8.0 for canaline-dependent OCT activity and Michaelis constants of 9.6 mM for canaline and 0.24 mM for carbamoyl phosphate. To some extent, the C-OCT also showed ornithine-dependent OCT activity and a pH optimum of 8.5; Michaelis constants for ornithine and carbamoyl phosphate were 0.21 and 0.086 mM, respectively. The enzyme exhibit V(max) for canaline-dependent activity 14-fold higher than that for ornithine-dependent activity and the ratio of canaline-dependent activity to ornithine-dependent activity was 66-fold higher than that of OCT of the same plant. It is likely that this enzyme plays an important role in the canavanine synthesis from the canavanine-containing plants.