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

Journal Article · Tue Jun 25 04:00:00 EDT 1985 · J. Biol. Chem.; (United States)

OSTI ID:6380851

Sitter, A J; Reczek, C M; Terner, J

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

• OSTI ID: 6380851
• Journal Information: J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 12; ISSN JBCHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
DEUTERIUM
ELEMENTS
ENZYMES
GLOBIN
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
IRON
ISOENZYMES
ISOTOPES
KINETICS
LIGHT NUCLEI
METALS
MYOGLOBIN
NONMETALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDOREDUCTASES
OXYGEN
PEROXIDASES
PH VALUE
PIGMENTS
PORPHYRINS
PROTEINS
RAMAN SPECTRA
REACTION KINETICS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENTS