Heme-linked ionization of horseradish peroxidase compound II monitored by the resonance Raman Fe(IV)=O stretching vibration.

摘要: Fe(IV)=O resonance Raman stretching vibrations were recently identified by this laboratory for horseradish peroxidase compound II and ferryl myoglobin. In the present report it is shown that frequency will switch between two values depending on pH, with pKa corresponding to previously reported heme-linked ionizations of = 6.9 isoenzyme A-2 8.5 C. Similar pH-dependent shifts myoglobin not detected above pH 6. The frequencies isoenzymes at transition points a high value approaching Below found be 10 cm-1 lower. Frequencies one set sensitive deuterium exchange below point but above. These results interpreted indicative an alkaline deprotonation distal amino acid group, probably histidine, which hydrogen bonded oxyferryl group point. Deprotonation disrupts bonding, raising frequency, proposed account lowering reactivity pH. vibration appears identical in what believed X.