tailieunhanh - Báo cáo khoa học: Mutual effects of proton and sodium chloride on oxygenation of liganded human hemoglobin Oxygen affinities of the a and b subunits

The different effects of pH and NaCl on individual O2-binding properties ofaandbsubunits within liganded tetramer and dimer of human hemo-globin (HbA) were examined in a number of laser time-resolved spectro-scopic measurements. A previously proposed approach [Dzhagarov BM & Lepeshkevich SV (2004)Chem Phys Lett390, 59–64] was used to determine the extent of subunit dissociation rate constant difference and subunit affinity difference from a single flash photolysis experiment. | ềFEBS Journal Mutual effects of proton and sodium chloride on oxygenation of liganded human hemoglobin Oxygen affinities of the a and b subunits Sergei V. Lepeshkevich and Boris M. Dzhagarov Institute of Molecular and Atomic Physics NationalAcademy of Sciences of Belarus Minsk Belarus Keywords a and b subunits affinity human hemoglobin molecular oxygen sodium chloride Correspondence . Dzhagarov Institute of Molecular and Atomic Physics NationalAcademy of Sciences of Belarus 70 Nezavisimosti Ave Minsk 220072 Belarus Fax 375 17 284 0030 Tel 375 17 284 1620 E-mail bmd@ Received 1 July 2005 revised 2 October 2005 accepted 6 October 2005 doi The different effects of pH and NaCl on individual O2-binding properties of a and b subunits within liganded tetramer and dimer of human hemoglobin HbA were examined in a number of laser time-resolved spectroscopic measurements. A previously proposed approach Dzhagarov BM Lepeshkevich SV 2004 Chem Phys Lett 390 59-64 was used to determine the extent of subunit dissociation rate constant difference and subunit affinity difference from a single flash photolysis experiment. To investigate the effect of NaCl concentration on the association and dissociation rate constants we carried out a series of experiments at four different concentrations and M NaCl over the pH range of the alkaline Bohr effect. As the data suggest the individual properties of the a and b subunits within the completely liganded tetrameric hemoglobin did not depend on pH under salt-free conditions. However different effects NaCl on the individual kinetic properties of the a and b subunits were revealed. Regulation of the O2-binding properties of the a and b subunits within the ligan-ded tetramer is proposed to be attained in two quite different ways. Normal adult human hemoglobin HbA is the classic textbook example of an allosteric protein. The HbA molecule is a heterotetramer consisting of two a .