Chromophoric derivatives of coenzyme MF 430, a proposed coenzyme of methanogenesis in Methanobacterium thermoautotrophicum

Abstract

Factors F 430 are nickel tetrapyrroles from methanogenic bacteria. Two methods are described to extract these compounds from cells of Methanobacterium thermoautotrophicum, namely, by boiling with 40% ethanol and by treatment of disrupted cells with HClO 4 at pH 2 and 0 °C. The subsequent purification procedures involving column chromatography are outlined. Ethanol extraction yielded one yellow compound which will be denoted coenzyme MF 430 (CoMF 430). Extraction with HClO 4 yielded a yellow derivative, called Factor F 430II, and a red component (F 560). In addition, a number of derivatives were prepared by preparative thin-layer chromatography, acid hydrolysis, and methanolysis of acid hydrolyzates. On the basis of ultraviolet-visible light absorption and mass spectral data, it was concluded that the methylated chromophores obtained by treatment of acid hydrolyzates are derivatives of Ni(II)sirohydrochlorin and its π-cation radical. Reduction studies and ultraviolet-visible light, 1H-NMR, and mass spectroscopy indicate that the chromophoric derivatives of CoMF 430 differ from the native compound with respect to the reduction level of the tetrapyrrole and the structural elements that are attached to the chromophore.