ヘムの異常代謝におけるグリーンピグメントのモデル錯体 : N-アルキルプロトポルフィリン-IX-コバルト(II)錯体を有する再構成ミオグロビン

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Cobalt (II) complexes of N-methyl and N-ethylprotoporphyrin IX dimethyl ester ((N-CH_3ProtoDME)Co(II)OAc and (N-C_2H_5ProtoDME)Co(II)OAc, OAc, acetate) have been prepared and characterized by ^1H-NMR measurements. Reconstitution of sperm whale apomyoglobin with the cobalt (II) complexes of N-methyl and N-ethylprotoporphyrin IX (OV-CH_3Proto)Co(II) and GV-C_2H_5Proto)Co(II)) afforded stable myoglobins ((N-CH_3Proto)Co(II)-Mb and N-C_2H_5Proto)Co(II)-Mb). The ^1H-NMR spectrum of GV-C_2H_5Proto)Co(II)-Mb indicated that proton signals assigned to the methyl group of N-ethyl group showed only two sharp signals of line width similar to that of the proton signals of peripheral methyl groups. This is suggestive that only two of the eight isomers of the complex were incorporated into the apomyoglobin. (N-CH_3Proto)Co(II)-Mb was reduced by dithionite under anaerobic condition. Electronic absorption spectrum of reduced product showed characteristic feature of organocobalt(III) porphyrin. This fact supports validity of intramolecularity of migration of N-substituent from pyrrolic nitrogen to the central metal ion in the cavity of protein.