Formation of compound I and compound II ferryl species in the reaction of hemoglobin I from Lucina pectinata with hydrogen peroxide

The formation of ferryl heme (Fe(IV) = 0) species, i.e., compound I and compound II, has been identified as the main intermediates in heme protein peroxidative reactions. We report stopped-flow kinetic measurements which illustrate that the reaction of hemoglobin I (HbI) from Lucina pectinata with hydrogen peroxide produce ferryl intermediates compound I and compound II. Compound I appears relatively stable displaying an absorption at 648 nm, The rate constant value (k'(2)) for the conversion of compound I to compound II is 3.0 x 10(-2) s(-1), more than 100 times smaller than that reported for myoglobin, The rate constant value for the oxidation of the ferric heme (k'(12) + k'(13)) is 2.0 x 10(2) M-1 s(-1). These values suggest an alternate route for the formation of compound II (by k',,) avoiding the step from compound P to compound II (k'(2)), In HbI from L, pectinata the stabilization of compound I is attribute to the unusual collection of amino acids residues (Q64, F29, F43, F68) in the heme pocket active site of the protein. (C) 2001 Academic Press.