Kinetic study of hemoglobin Porto Alegre [ß9(A6)SER-CYS] polymerization by inter-tetramer disulfide bond formation

RESUMO

The polymerization of hemoglobin Porto Alegre (HbPA) by inter-tetramer disulfide bond formation at pH 7.6 follows kinetics second order in Hb concnetration. The initial stage of the polymerization was associated with the formation of an HbPAS-S-S-HbPA octamer and a rate constant of 9 x 10***-2M***-1min***-1 was found at 13-C. A later stage of the polymerization wa associated with HbPA-S-S-HbPA-S-S-HbPA dodecamer formation and the rate constant calculated by an approximate treatment was found to be 2.8M***-1 at 13-C. The polymerization by intertetramer disulfide bond formation of HbPA in a 11 mixture with HbA follows second orfer kinetics and is monophasic. the lower rate constant found for the HbPA-S-S-HbA octamer (3.9 x 10***-2 M***-1min***-1 at 13-C) is attributed to the formation of S-S bond involving the thiols of the ß9 cysteine from HbPA and the ß93 cysteine from HbA. The 25.6 e.u. more positive "apparent" entropy of activation found for the dodecamer, when comapred to that of the HbPA-S-S-HbPA octamer, is interpreted as due to dehydration of electrically charged groups. The 15.6 e.u. more positive "apparent" entropy of activation of the HbPAS-S-HbA octamer when compared to that of the HbPA-S-S-HbPA octamer is also interpreted as due to dehydration