Dataset Information

Association of tetrapyrrole intermediates in the bacteriochlorophyll a biosynthetic pathway with the major outer-membrane porin protein of Rhodobacter capsulatus.

ABSTRACT: Rhodobacter capsulatus regulates synthesis of bacteriochlorophyll a in response to changes in oxygen partial pressure and light intensity. One early model proposed that this regulation involved a carrier polypeptide that functions to tether tetrapyrrole intermediates to the membrane. In the present study we isolated tetrapyrrole intermediates accumulated in three strains of R. capsulatus that contain mutations which block bacteriochlorophyll a biosynthesis at different steps of the magnesium branch of the pathway. Each of the tetrapyrrole intermediates was shown to be associated with the same 32 kDa polypeptide, as indicated by similar electrophoretic mobility and antigenic cross-reactivity with polyclonal antisera. The 32 kDa pigment-associated protein was further found to have an electrophoretic mobility, antigenic cross-reactivity and N-terminal sequence identical with those of the previously characterized major outer-membrane porin protein of R. capsulatus.

SUBMITTER: Bollivar DW

PROVIDER: S-EPMC1130803 | biostudies-other | 1992 Mar

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Background In many works, the chemical composition of bacterially-produced elemental selenium nanoparticles (Se0-nanoparticles) was investigated using electron dispersive X-ray analysis. The results suggest that these particles should be associated with organic compounds. However, a complete analysis of their chemical composition is still missing. Aiming at identifying organic compounds associated with the Se0-nanoparticles produced by the purple phototrophic bacteria Rhodospirillum rubrum and Rhodobacter capsulatus (? group of the proteobacteria), we used MALDI-TOF spectrometry.Results This technic revealed that numerous signals obtained from particles produced by both species of bacteria were from metabolites of the photosynthetic system. Furthermore, not only bacteriochlorophyll a, bacteriopheophytin a, and bacteriopheophorbide a, which are known to accumulate in stationary phase cultures of these bacteria grown phototrophically in the absence of selenite, were identified. The particles were also associated with intermediary metabolites of the bacteriochlorophyll a biosynthesis pathway such as protoporphyrin IX, protoporphyrin IX monomethyl ester, bacteriochlorophyllide a and, most likely, Mg-protoporphyrin IX-monomethyl ester, as well as with oxidation products of the substrates of protochlorophyllide reductase and chlorin reductase.Conclusion Accumulation of intermediary metabolites of the bacteriochlorophyll biosynthesis pathway in these purple phototrophic bacteria was attributed to inhibition of oxygen-sensitive enzymes involved in this pathway. Consistent with this interpretation it has been reported that these bacteria reduce selenite intracellularly, that they contain high levels of glutathione and that the reduction of selenite with glutathione is a very fast reaction accompanied by the production of reactive oxygen species. As many enzymes involved in the biosynthesis of bacteriochlorophyll contain [Fe-S] clusters in their active site, which are known to be degraded in the presence of reactive oxygen species as well as in the presence of molecular oxygen, we concluded that the substrates of these enzymes accumulate in cells during selenite reduction.Association of metabolites of bacteriochlorophyll biosynthesis and degradation with the Se0-nanoparticles produced by Rhodospirillum rubrum and Rhodobacter capsulatus is proposed to result from coating of the nanoparticles with the intracytoplasmic membrane of these bacteria, where the photochemical apparatus is concentrated.

Dataset Information

Association of tetrapyrrole intermediates in the bacteriochlorophyll a biosynthetic pathway with the major outer-membrane porin protein of Rhodobacter capsulatus.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure