title: Thermal stability of extracellular hemoglobin of Glossoscolex paulistus: determination of activation parameters by optical spectroscopic and differential scanning calorimetric studies.
abstract: Glossoscolex paulistus hemoglobin (HbGp) was studied by dynamic light scattering (DLS), optical absorption spectroscopy (UV-VIS) and differential scanning calorimetry (DSC). At pH 7.0, cyanomet-HbGp is very stable, no oligomeric dissociation is observed, while denaturation occurs at 56°C, 4°C higher as compared to oxy-HbGp. The oligomeric dissociation of HbGp occurs simultaneously with some protein aggregation. Kinetic studies for oxy-HbGp using UV-VIS and DLS allowed to obtain activation energy (E(a)) values of 278-262 kJ/mol (DLS) and 333 kJ/mol (UV-VIS). Complimentary DSC studies indicate that the denaturation is irreversible, giving endotherms strongly dependent upon the heating scan rates, suggesting a kinetically controlled process. Dependence on protein concentration suggests that the two components in the endotherms are due to oligomeric dissociation effect upon denaturation. Activation energies are in the range 200-560 kJ/mol. The mid-point transition temperatures were in the range 50-65 °C. Cyanomet-HbGp shows higher mid-point temperatures as well as activation energies, consistent with its higher stability. DSC data are reported for the first time for an extracellular hemoglobin.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, SP, Brazil.
authors.forename: Patrícia S
authors.initials: PS
authors.lastname: Santiago
authors.forename: José Wilson P
authors.initials: JW
authors.lastname: Carvalho
authors.forename: Marco M
authors.initials: MM
authors.lastname: Domingues
authors.forename: Nuno C
authors.initials: NC
authors.lastname: Santos
authors.forename: Marcel
authors.initials: M
authors.lastname: Tabak
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning; D006454:Hemoglobins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D009835:Oligochaeta / Q000378:metabolism*; D010084:Oxidation-Reduction; D011489:Protein Denaturation; D055550:Protein Stability; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet; D044366:Transition Temperature
chemical_list: D006454:Hemoglobins