The Role of Cytochromes and Blue Copper Proteins in the Oxidation of Methanol and Methylamine in Organism 4025, an Obligate Methylotroph

Abstract

Organism 4025 contained only b-type and c-type cytochromes. In the absence of any a-type cytochrome oxidase it was concluded that respiration in these bacteria is catalysed entirely by way of the o-type cytochrome oxidase. After growth on methanol, the soluble protein contained cytochromes cH and cL, and a single blue copper protein of unknown function, 'azurin'. After growth on methylamine the soluble proteins were strikingly different. The total concentration of soluble cytochrome c was about 70% lower; cytochrome cL was about 65%, and cytochrome cH about 16% of the concentrations present after growth on methanol. Although some 'azurin' was still present, a second copper protein, amicyanin (94% of the total), was induced during growth on methylamine. The concentration of this protein was considerably higher than that of blue copper proteins measured in other bacteria and 35 times higher than the concentration in the facultative methylotroph Pseudomonas AM1 during growth on methylamine. It is the very high concentration of amicyanin that gave suspensions of methylamine-grown organism 4025 their blue-green colour. All of the soluble cytochrome c, and all of the methanol dehydrogenase, methylamine dehydrogenase and blue copper proteins were located in the periplasmic fraction. All these results are consistent with the conclusion that the main electron acceptor for methylamine dehydrogenase in organism 4025 is amicyanin.

The blue copper protein gene of Alcaligenes faecalis S-6 directs secretion of blue copper protein from Escherichia coli cells

“…Its nucleotide sequence also encodes an NH2-terminal signal sequence of 19 amino acid residues. Periplasmic localization of amicyanin was also demonstrated in some methylotrophic bacteria (11,15). Most of the bacterial blue copper proteins might be secreted through the cytoplasmic membrane and play as electron carriers in the periplasm.…”

Physiology and genetics of methylotrophic bacteria

“…None of the conserved features of known c-type cytochromes could be detected apart from the home-binding site, which makes it unlikely that cytochrome c L is involved in a reaction with a terminal oxidase-This role seems reserved for cytochrome c H [7,69,8"?-89], but it remains possible that other components also contribute to the overall electron fl~,~v from methanol dehydrogenase to oxygen. Several redox proteins can be found in different amounts in the methylotrophs studied so far and the levels of individual components may vary depending on the growth condition of the methylotrophic ~,tganism under study [69,90]. Paracoccus denitrificans, when grown with methanol, has been shown to produce three membrane bound c-type cytochromes [91] and at least three individual types of soluble cytochrome c [92], two of which seem to be functionally homologous to cytochrome c L and cytochrome c u.…”

Microbial metabolism of C1-nitrogen compounds other than cyanide

“…Traces of an active carrier in a preparation of another carrier could lead to misleading results. • Moreover it also needs to be borne in mind that such experiments may be unphysiologicai in that certain of the components of the system (the dehydrogenase [21], amicyanln [22] and cytochromes CL and CH [23]) are on the perlplasmic surface of the membrane, while the terminal oxldase is on the cytoplasmic surface.…”