A BIOPHYSICAL CHARACTERIZATION OF THE IRON COORDINATION ENVIRONMENT IN WHEAT-GERM PEROXIDASE

The heme protein wheat germ peroxidase (isoenzyme C-2) and its cyanide -inhibited form have been investigated by means of electronic, CD and paramagnetic NMR spectroscopy. The data indicate a protein environment of the active site distinct from that of horseradish peroxidase (HRP) , with a larger solvent accessibility. The iron is pentacoordinated at neutral and low pH, whereas a hydroxyl anion may be bound at alkaline pH. The fifth axial ligand is a His residue with a partial anionic ch aracter, as found in other peroxidases. A spin equilibrium is observed at high enzyme concentrations.