Ornithine transcarbamylase of rat liver. Kinetic, physical, and chemical properties.

Ornithine transcarbamylase of rat liver has been purified to homogeneity. The purified enzyme of specific activity 870 to 920 focuses as a single protein at pH 7.2. At pH 7.7, the Km for carbamyl phosphate is 0.026 mM, and the Km for ornithine is 0.04 mM. The inhibition constants of a number of amino acids that act as competitive inhibitors of the enzyme are reported. The native enzyme of Mr = 112,000 is composed of three subunits of Mr = 39,600 +/- 1,000. Chemical evidence indicates that the subunits are identical in amino acid composition and amino acid sequence. The amino acid sequence of the NH2-terminal region of ornithine transcarbamylase is Ser-Gln-Val-Gln-Leu-Lys-Gly-Ser-Asp-Leu-Leu-Thr-Leu-Lys-Asn-(Phe)-X-Thr-X-Glu-Ile-Gln-Tyr-Met-.