The role of arginyl residues in porphyrin binding to ferrochelatase.
The role of cationic amino acid residues in the binding of porphyrin substrates by purified bovine ferrochelatase (protoheme ferro-lyase, EC 4.99.1.1) have been examined via chemical modification with camphorquinone-10-sulfonic acid, phenylglyoxal, butanedione, and trinitrobenzene sulfonate. The data obtained show that modification of arginyl, but not lysyl, residues results in the rapid inactivation of ferrochelatase. The 2,4-disulfonate deuteroporphyrin, which is a competitive inhibitor of mammalian ferrochelatase, protects the enzyme against inactivation. Ferrous iron has no protective effect. Reaction with radiolabeled phenylglyoxal shows that modification of 1 arginyl residue causes maximum inhibition of enzyme activity. The inactivation does not follow simple pseudo-first order reaction kinetics, but is distinctly biphasic in nature. Comparison of the enzyme kinetics for modified versus unmodified enzyme show that modification with camphorquinone-10-sulfonic acid has no effect on the Km for iron but does alter the Km for porphyrin.
H A
HA
Dailey
J E
JE
Fleming
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001120:Arginine; D001665:Binding Sites; D002164:Camphor / Q000031:analogs & derivatives / Q000494:pharmacology; D002417:Cattle; D005294:Ferrochelatase / Q000378:metabolism*; D007202:Indicators and Reagents; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008190:Lyases / Q000378:metabolism*; D010658:Phenylglyoxal / Q000494:pharmacology; D011166:Porphyrins / Q000378:metabolism*; D011485:Protein Binding
D000596:Amino Acids; D007202:Indicators and Reagents; D011166:Porphyrins; C023633:camphorquinone-10-sulfonic acid; D002164:Camphor; D001120:Arginine; D008190:Lyases; D005294:Ferrochelatase; D010658:Phenylglyoxal