To understand effect of (-stacking interactions between the side chain of aromatic amino acids and the porphyrin ring on structures and properties in cytochrome b5 (cyt b5), the Phe58 residue was mutated to tyrosine and tryptophan, respectively by site-directed mutagenesis. The denaturation of cyt b5 F58W and F58Y toward guanidine hydrochloride was examined by UV-visible and fluorescence spectroscopy. The kinetics of heme transfer reactions between apo-myoglobin and the mutants were studied. The results indicated that the mutation of F58 residue for Y58 or W58 reduced the interaction between of peptide and the heme group, resulting in decrease of the Tm and Cm values of the proteins, increase of the heme transfer reaction rate, and shifts of the redox potential.