The Influence of the Peptide Chain on the Kinetics and Stability of Microperoxidases

Microperoxidases with increasing lengths of the peptide attached to the heme moiety have been isolated after proteolytic digestion of horse‐heart cytochrome c (microperoxidases 6, 8, and 11) and of cytochrome c550 from Thiobacillus versutus (microperoxidase 17). The different microperoxidases catalyze the H2O2‐dependent para ‐hydroxylation of aniline relatively efficiently but are rapidly inactivated under turnover conditions. The horse‐heart cytochrome‐c ‐derived microperoxidases have identical values for Vmax but show a decrease of the Km, for aniline and a higher stability when the attached peptide is longer. The kinetic constants obtained for microperoxidase 17, differ markedly from the microperoxidases derived from horse‐heart cytochrome c. Possible factors underlying the observed differences are discussed.