| Autor: |
Robert Bierme, Joëlle Thillet, Jean Rosa, Marie Claude Garel |
| Rok vydání: |
1980 |
| Předmět: |
|
| Zdroj: |
Biochimica et Biophysica Acta (BBA) - Protein Structure. 624:293-303 |
| ISSN: |
0005-2795 |
| DOI: |
10.1016/0005-2795(80)90248-2 |
| Popis: |
We have studied the oxidation properties of two unstable hemoglobin variants: Hb Castilla ( β32 ( B 14) Leu → Arg ) and Hb Toulouse ( β66 ( E 10) Lys → Glu ). Hb Castilla, a very unstable variant, exhibited a rapid autoxidation rate with a concomitant appearance of hemichrome and precipitation. Inositol hexaphosphate increases the percentage of hemichrome in the ferriform of Hb Castilla. This could be interpreted either as a direct action on the oxidation step leading to hemichrome or as a displacement of the equilibrium towards a more readily oxidized conformation. Hb Toulouse also autoxidized very rapidly but did not form hemichrome. The ionization p K of the ferric form was increased (8.5 instead of 8.1 for normal) due to the more acidic environment of the iron. The reduction rates of these hemoglobins by enzymatic systems differed; thus Hb Castilla was completely reduced while Hb Toulouse remained 50% in the ferriform. Although each Hb displays an amino acid substitution which probably explains their instability, the perturbations are different in the two cases. These results are discussed in view of the differences in the stereochemical modifications of the two hemoglobins and also with regard to the general mechanism of denaturation of hemoglobins proposed by Winterbourn and Carrell ((1974) J. Clin. Invest. 54, 678). For the study of the functional properties of Hb Castilla, we have developed a method which minimized precipitation and oxidation: the use of an enzymatic reducing system prevented oxidation and temperature of experiment was decreased to 10°C in order to diminish the precipitation. Under these conditions, Hb Castilla exhibited a decreased oxygen affinity, a low degree of subunit interaction and a decreased Bohr effect. Variations in P 50 were also studied as a function of temperature. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
