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Studies on the reaction of haptoglobin with hemoglobin and hemoglobin chains

1970; Elsevier BV; Volume: 200; Issue: 1 Linguagem: Inglês

10.1016/0005-2795(70)90045-0

1878-1454

Annette Alfson, Emilia Chiancone, Jeffries Wyman, Eraldo Antonini,

Quantum, superfluid, helium dynamics

The kinetics of the reaction of haptoglobin with hemoglobin and hemoglobin chains has been studied by fluorescence quenching in a stopped-flow apparatus. The reaction with the isolated α-chains appears to be second order, as if the haptoglobin molecule had four equivalent independent binding sites. This is in agreement with previously reported equilibrium measurements. Experiments in which the α- and β-chains are added to haptoglobin in that sequence conform the conclusion that the β-chains have a high affinity for haptoglobin only in the presence of α-chains. The principal new finding is the inverse relationship between the rate of the reaction and the concentration of haptoglobin or oxyhemoglobin when the concentration of the other reagent is held constant. When oxyhemoglobin is in excess this effect may possibly be due to an association-dissociation equilibrium of the haptoglobin molecule. When haptoglobin is in excess the situation is more complicated due to the existence of two haptoglobin hemoglobin complexes, and also to the presence of an association-dissociation equilibrium in hemoglobin.