When grown on blood-containing solid media, the anaerobic periodontal pathogen Porphyromonas gingivalis produces a haem pigment, the major component of which is the μ-oxo bishaem of iron protoporphyrin IX [Smalley, Silver, Marsh and Birss (1998) Biochem. J. 331, 681–685]. In this study, μ-oxo bishaem generation by P. gingivalis from oxy- and deoxyhaemoglobin was examined. Bacterial cells were shown to convert oxyhaemoglobin into methaemoglobin, which was degraded progressively, generating a mixture of both monomeric and μ-oxo dimeric iron protoporphyrin IX. The rate of methaemoglobin formation was accelerated in the presence of bacterial cells, but was inhibited by N-ethylmaleimide and tosyl-lysylchloromethylketone. Interaction of cells with deoxyhaemoglobin resulted in formation of an iron(III) haem species (Soret λmax, 393nm), identified as pure μ-oxo bishaem.

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