GELATION OF SICKLE-CELL HEMOGLOBIN .4. PHASE-TRANSITIONS IN HEMOGLOBIN S GELS - SEPARATE MEASURES OF AGGREGATION AND SOLUTION-GEL EQUILIBRIUM
GELATION OF SICKLE-CELL HEMOGLOBIN .4. PHASE-TRANSITIONS IN HEMOGLOBIN S GELS - SEPARATE MEASURES OF AGGREGATION AND SOLUTION-GEL EQUILIBRIUM
复制标题
DOI：
10.1016/0022-2836(78)90205-x
复制
发表时间：
1978-01-01
影响因子：
5.6
通讯作者：
BRIEHL, RW
中科院分区：
文献类型：
--
作者：
BRIEHL, RW
Two assays of equilibrium properties in the gelation of [human] deoxyhemoglobin S were carried out by analytical ultracentrifugation on the same sample. Csat, the monomer concentration in equilibrium with the fully formed gel, was obtained as the supernatant concentration after sedimentation of a preformed gel. Presence of a plateau region during sedimentation of the supernatant and the rate of sedimentation of the boundary from which Csat was measured indicated that centrifugation did not alter the pre-existing equilibrium and that the supernatant consisted of monomers. The centrifugation was then continued to equilibrium to obtain a distribution showing a sharp increase in MW at Cagg, the monomer concentration at which a small amount of polymerization to large aggregates begins. The primary result was that Csat > Cagg under all conditions. The different values of the 2 parameters indicated that they reflect 2 separate transitions and that the overall monomer to gel process had a limited cooperativity. Within the limits of the method Csat was independent of total Hb concentration. The 2 transitions divided the overall range of total Hb concentration into an essentially monomeric region at concentrations below Cagg, a region in which isotropically oriented polymers exist, occurring when monomer concentration lies between Cagg and Csat, and a 2-phase region of conjugate isotropic and anisotropic phases when monomer concentration equals Csat. These regions corresponded to zones in the ultracentrifuge equilibrium distribution. In this scheme Cagg depended only on the interaction energy of polymerization. Csat depended on entropic factors which induce tactoid formation as well. Csat, while a monomer concentration, reflected a saturation not of monomers in relation to a polymeric phase, but of polymers in the isotropic phase in relation to the anisotropic or tactoidal polymerized phase. Csat represented a supersaturated state of isolated monomers. The ratio Csat/Cagg = 1.23 in stripped Hb and equilibrium distributions in the zone of isotropically oriented polymers were used to obtain an order of magnitude estimate of polymer size, found to be much smaller than that of Hb S fibers. This further confirms that gelation does not consist of a single transition and phase change with near infinite cooperativity of polymerization. Csat as well as Cagg were lowered by 2,3-diphosphoglycerate and inositol hexaphosphate. Decreasing pH near 7 also favored gelation. In stripped Hb a pH optimum for gelation occurred near pH 6.8. The apparent van''t Hoff .DELTA.H [enthalpy] for stripped Hb was about 3 kcal/mol for Csat and 2 kcal/mol for Cagg.
