SITE-DIRECTED MUTAGENESIS IMPROVES THE BIOCATALYTIC ACTIVITY OF ISO-1-CYTOCHROME-C IN POLYCYCLIC-HYDROCARBON OXIDATION

iso-1-Cytochrome c from Saccharomyces cerevisiae is able to oxidize po lycyclic aromatic hydrocarbons (PAH) in the presence of hydrogen perox ide. Anthracene and pyrene are oxidized by yeast cytochrome c to form anthraquinone and 1,8-pyrenedione, respectively. Iso-1-cytochrome c fr om S. cerevisiae was modified by site-directed mutagenesis of Phe82 an d Cys102. The Phe82 substitution significantly altered the kinetic beh avior of the protein; Cys102 modification affected neither the kinetic nor the stability constant. The Gly82;Thr102 valiant was 10 times mor e active and showed a catalytic efficiency 10-fold greater than the wi ld-type iso-1-cytochrome c. However, Phe82 variants showed lower stabi lity against inactivation by hydrogen peroxide than the wild-type prot ein. These site-directed mutations did not significantly alter the sta bility and activity of the hemoprotein in increasing concentrations of tetrahydrofuran.