Inhibition of carbamoyl-phosphate synthase (ammonia) by Tris and Hepes. Effect on <i>K</i>a for <i>N</i>-acetylglutamate

Abstract

The apparent Ka for N-acetylglutamate of rat liver carbamoyl-phosphate synthase is 11 microM in phosphate buffer, a value 10-fold lower than reported in other buffer systems. Tris and Hepes inhibit competitively with N-acetylglutamate. The proportion of carbamoyl-phosphate synthase in the active enzyme-acetylglutamate complex in vivo may be higher than previous calculations suggest, which re-opens the question of the involvement of N-acetylglutamate in the regulation of urea synthesis.