Sirohydrochlorin.1 Prosthetic Group of Sulfite and Nitrite Reductases and Its Role in the Biosynthesis of Vitamin B12

Isolation of metabolites from cobalt-free incubations of Propionibacterium shermanii extracts has uncovered a new intermediate (C42H46N4O16) related to the corrin biosynthetic pathway whose physical properties are identical with those of sirohydrochlorin. Structural proposals utilizing 13C NMR and 1H NMR spectra for this compound, which is the prosthetic group of a number of six-electron reducing enzymes, are discussed and the intermediacy of sirohydrochlorin in corrin biosynthesis is demonstrated in a double-labeling experiment. On the basis of these findings the complete stereostructure (7) is proposed for sirohydrochlorin and hence siroheme, the novel iron-containing prosthetic group of Escherichia coli NADPH-sulfite reductase (EC 1.8.1.2) and of ferredoxin-nitrite reductase (EC 1.7.7.1) of spinach. © 1978, American Chemical Society. All rights reserved.

Duke Scholars

Author Lewis M. Siegel Biochemistry