Õulgaris nitrate reductase: signal assignment of the heme moiety

Ž . A water soluble truncated heme domain a tetramer of MWs45 kDa of the tetrameric nitrate reductase complex from the green alga Chlorella Õulgaris has been overexpressed and purified. This truncated heme domain with four identical Ž . subunits has a high redox potential midpoint potential E sq16 mV as compared with other heme-containing 1r2 flavoproteins. We have undertaken a determination of the detailed configuration of the heme moiety in order to understand the unique electrochemical property of the heme moiety of this enzyme. We report here the study of the heme prosthetic group of the truncated heme domain by the use of 2D H and C NMR techniques. A complete signal assignment of the heme has been achieved. Our observations suggest that the heme configuration is similar to that of the crystal structure of the membrane-bound bovine liver cytochrome b . q 1998 Elsevier Science B.V. 5 ( )