In this paper, most of spin systems for amino acid residues in V45H, a site-directed mutant of cytochrome b5 where the residue Val^45 is mutated to His^45, have been indentified through analysis of 2D NMR 1^H-1^H DQF -COSY, TOCSY and NOESY spectra acquired in H2O and D2O. The sequence-specific assignment of spin systems is obtained by dNN (i,i+1), dαN(i,i+1), dαN(i,i+2), dαN(i,i+3),dαβ(i,i+3) and dβN(i, i+1) NOEs correlation found in NOESY spectra and the complete assignment of proton resonances for the backbone and side chain have been achieved. The analysis of secondary structure of V45H reveals that the mutation from Val^45 has little effect in the global folding of the protein. However, the chemical shift index of amide protons of V45H in comparson to those of wild type cytochrome b5 indicates that the heme pocket environment is disturbed by the mutation. These experimental results provide a basis for further determination of the solution structure of V45H and the roles of residue Val^45 in the protein.

Key words: HEME, PROTEIN