Chicken Ornithine Transcarbamylase: Purification and Some Properties

抄録

Ornithine transcarbamylase [EC 2. 1. 3. 3] has been purified from chick kidney to homogeneity. The molecular weight is 110, 000 as determined by gel filtration. Sodium dodecylsulfate polyacrylamide gel electrophoresis of the enzyme showed that the enzyme exists as a trimer of identical subunits of 36, 000 daltons like other mammalian species ornithine transcarbamylases. In 0.1M triethanolamine/HCl, the apparent optimum pH of the purified enzyme was 7.5 in the presence of 5mM ornithine. The curve shifted toward a more alkaline region with a decrease in ornithine concentration. The specific activity of the purified enzyme was 77 units at pH 7.5. The K_m for carbamyl phosphate was 0.11mM and the Km for ornithine was 1.21mM. With an increase in pH, a decrease in K_m values for ornithine and an increase in the extent of inhibition by ornithine were observed. On using antibody against bovine liver ornithine transcarbamylase, the precipitin lines for the chick and bovine enzymes showed a spur pattern. Even when excess amounts of the antibody were added, the chick enzyme did not lose the activity while the bovine enzyme activity was inhibited completely.