Elucidation of Reaction Mechanism of Abnormal Heme Metabolism utilizing Synthetical Technique

The reconstitution of apomyoglobin with 1.6 equivalent of Co(II)complexes of N_A-and N_B-ethylmesoporphyrin afforded stable myoglobins (N_A-C_2H_5Meso)Co(II) and (N_B-C_2H_5Meso)Co(II)-Mb. The ^1H-NMR spectrum showed three signals at -34.75ppm, -36.63ppm and -48.61ppm assigned to the methyl group of N-ethyl group, respectively. The signals at -34.75, -36.63 and -48.61ppm are assigned to the N_A-C_2H_5 of reverse orientation, N_B-C_2H_5 of normal orientation and N_B-C_2H_5 of reverse orientation, respectively. It seems that the steric repulsion of N_B-ethyl group with isopropyl group of Val 68 in myoglobin is larger than that of N_A-ethyl group is responsible for the relative abundance (1 : 0.4) of N_A- and N_B-ehyl group of reverse orientation. In addition, it seems that the relative abundance (1 : 2) of N_A-ethyl group of reverse orientation and N_B-ethyl group of normal orientation is consistent with the view that the N-ethylmesoporphyrin of normal orientation is preferentially reconstituted with myoglobin because the heme pocket of myoglobin recognize the sequence of side chains of N-alkylmesoporphyrin. From these results, it can be seen that the apomyoglobin recognizes a pair of enantiomers of N-alkylmesoporphyrin by the asymmetric heme pocket, and that the steric repulsion of N-ethyl group with Val 68 play an important role in the asymmetric recognition