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Extracellular metal free corrinoids from rhodopseudomonas sphaeroides


, : Extracellular metal free corrinoids from rhodopseudomonas sphaeroides. Journal of Biological Chemistry 255(16): 7637-7644

R. sphaeroides, when grown on a medium deficient of cobalt, excretes significant amounts of descobaltocorrinoids into the culture broth. If grown in the presence of 4 .mu.M CoCl2 only intracellular Co-containing corrinoids are detected. The extracellular corrinoids were identified as hydrogenobyrinic acid c-amide and hydrogenobyrinic acid a,c-diamide, which are accompanied by varying amounts of the corresponding 13-epicorrinoids. The latter, which could not be separated in the metal-free form, are artifacts arising from the excreted descobaltocorrinoids under the alkaline conditions of the culture broth. The red, metal-free corrinoids were converted into the corresponding Co-containing corrinoids and were characterized by their CD [circular dichroic], UV, 1H NMR and 13C NMR spectra. Insertion of Co into the fraction of hydrogenobyrinic acid c-amide has yielded small amounts of a Co-containing corrinoid, for which the structure of 18,19-didehydrocobyrinic acid c-amide is suggested. A 14C-labeled specimen of hydrogenobyrinic acid a,c-diamide was obtained by feeding [14C]acetate to growing cultures of R. sphaeroides. Experiments with broken cells systems of Propionibacterium shermanii [Freudenreichii] and R. speroides indicated that metal-free corrinoid are not precursors of the cobamides. The results are discussed with respect to the final steps of the biosynthesis of vitamin B12.

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PMID: 6967486


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