MUTATION OF THE DISTAL ARGININE IN COPRINUS-CINEREUS PEROXIDASE - STRUCTURAL IMPLICATIONS

Heme peroxidases of prokaryotic, plant and fungal origin share the ess ential His and Arg catalytic residues of the distal cavity and a proxi mal His bound to heme iron, Spectroscopic techniques, in contrast to X -ray crystallography, are well suited to detect the precise structure, spill and coordination states of the hem as influenced by its near en vironment. Resonance Raman and electronic absorption spectra obtained at various pH values for Fe3+ and Fe2+ forms of distal Arg51 mutants o f the fungal Coprinus cinereus peroxidase are reported, together with the fluoride adducts at pH 5.0. This basic catalytic residue has been replaced by the aliphatic residue Leu, the polar residues Asn and Gin and the basic residue Lys (Arg51 --> Leu, Asn, Gln, and Lys, respectiv ely), These mutations cause changes in the coordination and spin state s of the heme iron, and in the v(Fe-Im) stretching frequency. The vari ations are explained in terms of pH-dependent changes, charge location , size and hydrogen-bonding acceptor/donor properties of the residue a t position 51. The present work indicates that the hydrogen-bond capab ility of the residue in position 51 influences the occupancy of water molecules in the distal cavity and the ability to form stable complexe s between anionic ligands and tile heme Fe atom.