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Doctor of Philosophy




The reactions of NO and NO(,2)('-) with the nonheme oxygen carrier, hemerythrin (Hr), were studied in order to shed further light on two physiological functions of Hr: reversible oxygenation and auto-oxidation;A green-colored nitric oxide adduct of deoxyHr (deoxyNO) results from the reactions of NO with deoxyHr and oxyHr. The quadrupole doublets observed in the Mossbauer spectrum are assigned to an S = 2 Fe('2+) center and an S = 3/2 FeNO ('7) site. Low-temperature broadening of both doublets and the occurrence of a novel EPR signal indicate that these two sites are antiferromagnetically coupled to produce an S(,eff) = 1/2 ground state. Identification of (nu)(Fe-NO) and (delta)(Fe-N-O) in the resonance Raman spectrum is consistent with end-on coordination of NO to iron. The downward shift of (delta)(Fe-N-O) in D(,2)O indicates that the ligand engages in hydrogen-bonding with the (mu)-hydroxo group and is consistent with a bent Fe-N-O geometry. Formulation of the oxidation states as Fe('2+)Fe('3+)NO('-) is analogous to that of a putative Fe('2+)Fe('3+)O(,2)('-) intermediate of the oxygenation reaction. As such, these results suggest that during oxygenation, the iron atoms are antiferromagnetically coupled prior to formal oxidation of the second iron atom;When NO is added to deoxyF('-), a more stable adduct (deoxyF('-)NO) results. Evidence suggests that a (mu)-fluoro bridge has replaced the (mu)-hydroxo bridge of deoxyNO. The relative affinities of deoxyHr, deoxyF('-), and semi-metHr for NO could provide a basis for delineation of the factors that affect the affinity of Hr for oxygen;The reaction of deoxyHr with NaNO(,2) occurs in two phases. The first phase (k(,1) = 2.10 M('-1)s('-1) at pH 6.58) produces a brown, EPR-silent product. This product, identified as semi-metNO, was also prepared by adding NO to semi-metHr. The second phase (k(,2) = 6.11 x 10('-4) s('-1)) at pH 6.58) is attributed to rate-limiting loss of NO followed by the rapid binding of NO(,2)('-). The final product is a paramagnetic nitrite adduct of semi-metHr, semi-metNO(,2)('-). In contrast to all the other oxidants used to date (besides O(,2)), nitrite reacts directly at the iron center of deoxyHr in an "inner sphere" fashion. Semi-metNO(,2)('-) is also detected when oxyHr is auto-oxidized to metHr in the presence of nitrite, which suggests that deoxyHr may be an intermediate in auto-oxidation.



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Judith Mary Nocek



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334 pages