COORDINATION OF AMINO-ACIDS BY THE FE-3+ PORPHYRIN MICROPEROXIDASE-8 - POSSIBLE ROLE FOR THE INVARIANT PHE IN THE PEROXIDASE ENZYMES

Equilibrium constants have been determined for the substitution of coordinated H2O in the Fe3+ MP-8 by various amino acids in 20% aqueous MeOH at 25-degrees-C; the presence of an aromatic side chain significantly increases log K from, e.g. Gly 3.5 to Phe 4.8 and Trp 5.6 and causes a shift in the wavelength of the Soret band from 403 to 406 nm, which is ascribed to donor-acceptor interaction between the porphyrin and aromatic/heterocyclic rings and suggests a role for the invariant distal Phe in the peroxidases.