title: Solubility of fluoromethemoglobin S: effect of phosphate and temperature on polymerization.
abstract: The polymerization properties of the fully liganded fluoromet derivative of hemoglobin S (FmetHb S) were investigated by electron microscopy and absorption spectroscopy. Polymerization progress curves, as measured by increasing sample turbidity at 700 nm, exhibit a delay time (t(d)) consistent with the double nucleation mechanism. The pattern of fiber growth, as monitored by electron microscopy, is also indicative of a heterogeneous nucleation process, and dimensions of the fibers were found to be comparable to that of deoxyHb S. The polymerization rate constant (1/t(d)) depends exponentially on Hb S concentration, and the size of the homogeneous and heterogeneous nuclei also depend on FmetHb S concentration. As for deoxyHb S, higher concentrations of protein and phosphate favor fiber formation, while lower temperatures inhibit polymerization. Solubility experiments reveal, however, that eight times more FmetHb S is required for polymerization. The current studies further show that reaction order is independent of phosphate concentration if Hb S activity and not concentration is considered. The allosteric effector, inositol hexaphosphate (IHP), promotes fiber formation, and temperature-dependent reaggregation of FmetHb S suggests that IHP stabilizes pregelation aggregates. These studies show that FmetHb S resembles deoxyHb S in many of its polymerization properties; however, IHP-bound FmetHb S potentially provides a unique avenue for future studies of the early stages of Hb S polymerization and the effect of tertiary and quaternary protein structure on the polymerization process.
authors.affiliation: Molecular Biology and Biochemistry Department, Molecular Biophysics Program, Wesleyan University, Middletown, Connecticut 06459-0175, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Yohe
authors.forename: K M
authors.initials: KM
authors.lastname: Sheffield
authors.forename: I
authors.initials: I
authors.lastname: Mukerji
mesh_terms: D000494:Allosteric Regulation; D006441:Hemoglobin A / Q000737:chemistry; D006451:Hemoglobin, Sickle / Q000737:chemistry* / Q000648:ultrastructure*; D006801:Humans; D007700:Kinetics; D008706:Methemoglobin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000648:ultrastructure; D008854:Microscopy, Electron; D009391:Nephelometry and Turbidimetry; D010833:Phytic Acid / Q000494:pharmacology*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012995:Solubility; D013053:Spectrophotometry; D013816:Thermodynamics
chemical_list: D006451:Hemoglobin, Sickle; C030944:fluoro-methemoglobin; D010833:Phytic Acid; D008706:Methemoglobin; D006441:Hemoglobin A