Aggregation of ferrihaems. Dimerization and protolytic equilibria of protoferrihaem and deuteroferrihaem in aqueous solution

Abstract

1. The absorption spectra of deutero- and proto-ferrihaem in aqueous solution at 25 degrees C show marked changes with concentration and pH in the Soret band region. Quantitative studies of these phenomena imply that they are associated with ferrihaem dimerization and with protolytic equilibria involving monomeric (M) and dimeric (D) ferrihaem species according to the scheme: [Formula: see text] 2. For deuteroferrihaem we obtain K=1.9x10(-2), pK(a(M))=7.1, pK(a(D))=7.4. Protoferrihaem has a much higher dimerization constant, K=4.5 and pK(a(D))=7.5 (pK(a(M)) is not accessible). 3. Possible structural relationships between monomeric and dimeric ferrihaem species in solution are discussed in relation to recent work on the oxo-bridged nature of crystalline ferrihaem dimers.

Interactions of hemin, antimalarial drugs and hemin-antimalarial complexes with phospholipid monolayers

“…Since FP exists mostly as dimers at the FP concentration range used [32], it can be concluded from the power dependence that when the monolayer is expanded (low hi), FP is able to intercalate as a dimer, and when the monolayer is compressed, the power monotonically decreases, until finally, at 7ri-values comparable to those estimated for erythrocyte membranes [24], it approaches 1, implying that FP intercalates as a monomer. The largest differences between the various phospholipids are observed in expanded monolayers and, as 7r i is raised, these differences vanish.…”

Stability of the Heme-Globin Linkage in αβ Dimers and Isolated Chains of Human Hemoglobin

“…3) depends linearly on albumin concentration up to approximately 25 M; at higher protein concentrations a constant value of 1.3 s Ϫ1 is reached. This value, which relates to a rate-limiting monomolecular step, is close to the rate of hemin depolymerization (18). From the data in Fig.…”

Detection of Heme-Binding Proteins in Epidemic Strains of Burkholderia cepacia

“…In addition, any FePPIX bound to the cell surface or the HBP in the -oxo bisheme (dimeric) form would dissociate at these lower pHs to give the monomeric species, which is more catalase active (19). One important property of both monomeric and dimeric hemes is their ability to aggregate (7). Bacterial cell surface heme aggregates would provide both a physical and chemical barrier resistant to H 2 O 2 and other reactive oxidants.…”