SPECTROSCOPIC CHARACTERIZATION OF FE-57-RECONSTITUTED RUBRERYTHRIN, ANONHEME IRON PROTEIN WITH STRUCTURAL ANALOGIES TO RIBONUCLEOTIDE REDUCTASE

Rubrerythrin, a contraction of rubredoxin and hemerythrin, is the triv ial name given to a non-heme iron protein isolated from Desulfovibrio vulgaris (Hildenborough). This protein, whose physiological function i s unknown, was first characterized by J. LeGall et al. [(1988) Biochem istry 28, 1636] as being a homodimer of subunit M(r) = 21 900 with fou r Fe per homodimer distributed as two rubredoxin-type FeS4 centers and one hemerythrin-type diiron cluster. Subsequent analysis of the amino acid sequence of the rubrerythrin gene [Kurtz, D. M., Jr., & Prickril , B. C. (1991) Biochem. Biophys. Res. Commun. 181, 137] revealed an in ternal homology which suggested that each subunit can accommodate one diiron cluster. Here, we report a procedure for reconstitution of the as-isolated D. vulgaris rubrerythrin with Fe-57. The reconstituted pro tein was characterized by optical, electron paramagnetic resonance, an d Mossbauer spectroscopies. The results indicate successful incorporat ion of Fe-57 into the two types of sites and strongly suggest that eac h subunit of rubrerythrin can indeed accommodate one diiron cluster as well as one rubredoxin-type center. Combined with amino acid sequence analysis, the spectroscopic characterization further suggests that th e rubrerythrin subunit contains a diiron site whose structure is more closely related to that in ribonucleotide reductase than to that in he merythrin.