Models of heme D/sub 1/. Structure and redox chemistry of dioxoisobacterioclorins

Unlike the ubiquitous iron porphyrin containing cytochromes found in animals and plants, d-type cytochromes present in many microbial nitrite reductases-cytochrome oxidases contain a green heme prosthetic group whose structure has been assumed for the last 2 decades to be a chlorin (dihydroporphyrin). On the basis of spectroscopic data collected by Timekovich et al., one of the authors (C.K.C.) has recently proposed that heme d/sub 1/ isolated from pseudomonas aeruginosa and Parracoccus denitrificans is not a chlorin but a dioxoisobacteriochlorin. Crucial to this assignment is a model compound, 3,8-dioxo-2,2',7,7',12,13,17,18-octaethylporphyrin (dioxo iBC), which exhibits many diagnostic NMR and absorption spectral features also possessed by the natural d/sub 1/ pigment. As part of an investigation to establish the validity of this proposal, reported here are physicochemical properties of several oxoporphyrin derivatives, a family of compounds that has received little attention, hitherto. 17 references, 1 figure, 1 table.