EFFECT OF COVALENT MODIFICATION ON COPROPORPHYRINOGEN OXIDASE FROM CHICKEN RED-BLOOD-CELLS

The biosynthesis of heme is a complex multi-step pathway requiring the efforts of eight enzymes. The initial enzymes in the heme biosyntheti c pathway have been well characterized in relation to their mechanisms . Coproporphyrinogen oxidase (Copro'gen oxidase) is one of the last th ree enzymes in the pathway and is one of the least well understood. Co pro'gen oxidase converts coproporphyrinogen III to protoporphyrinogen IX via oxidative decarboxylation of the 3- and 8- propionic side chain moieties. To further our understanding of the recognition and binding of substrate, Copro'gen oxidase was partially purified from chicken r ed blood cell hemolysates then incubated with covalent modifiers of sp ecific amino acids. Incubation with tetranitromethane, p-hydroxyphenyl glyoxal, N-acetylimidazole, or trinitrobenzenesulfonic acid resulted i n substantial reduction of Copro'gen oxidase activity implying the pre sence of critical tyrosine, arginine and lysine residues. We conclude that these amino acids play important roles in the enzymic mechanism ( for both binding and catalysis) of Copro'gen oxidase.