Heme Fe II NO Subunit Selectivity

The remarkable aspect of the chemistry that we have reported is the preferential population of P-subunit hemes, primarily in largely oxidized [24] or oxygenated [12,40] Hbs. We have reported that gradual decomposition of the SNO moiety in neat solutions of SNO-oxy-Hb, as well as more rapid reactions accelerated by added reductants, results in autocapture of NO on the P-subunits [12,40,48]. Selectivity is essentially complete. This effect appears to be governed by the proximity of the P-cys 93 and heme-iron reduction of co-solute low-molecular-weight nitro-sothiols in oxy-Hb solutions results in very limited heme-Fe(II)NO yield and no subunit-selectivity [48]. Similarly, the reaction of deoxy-Hb with low-levels of nitrite [24], 

This reaction cycle underscores flic previously unanticipated flexibility that exists in positioning flic NO-group on the Hb tetramer, and subtlety of NO interactions with Hb. The Hb [(a-Fe(ll)NO)2(P-Fe(ni))2] hybrid can be reduced to furnish Hb[(a-Fe(Il)NO)2(P-Fe(ll))2], which is predominately comprised of five coordinate nitrosyl-hemes, as is evident from flic characteristic EPR signature apparent in 

The spectral editing of EPR contributions from the different subunits marks a speetroseopie milestone. It is, however, an intriguing surprise that heme-nitrosyl speeies within the different subunits exhibit saturation-recovery times that are suf-fieiently different to enable their spectroscopic separation. In continuing work, we are extending this editing methodology to probe for species, such as met/nitrosyl hybrids, that have been postulated as precursors for redox-coupled SNO-Hb formation [12,24,84,85] and for release of NO from SNO-Hb [86,87]. 

This ehapter details EPR experiments—some vintage and some new—that eontinue to assist in the development of a new perspective on the function of hemoglobin in humans, or more broadly, in organisms with mature cardiovascular 

This work was supported by National Science Foundation Grant MCB 0981228 (to D.J.S) and National Heart, Lung, and Blood Institute Grant ROl HL421444to J.S.S). 

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