Laser Kinetic Spectroscopy Studies of the Bimolecular Oxygenation of alpha- and beta-Subunits within the R-State of Human Hemoglobin

S. V. Lepeshkevich¹, N. V. Konovalova², and B. M. Dzhagarov^1*

¹Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, pr. F. Skaryny 70, Minsk 220072, Belarus; fax: (10-375-17) 284-0030; E-mail: lepeshkevich@imaph.bas-net.by or bmd@imaph.bas-net.by

²Institute of Biochemistry, National Academy of Sciences of Belarus, ul. Leninskogo Komsomola 50, Grodno 230009, Belarus; fax: (10-375-152) 33-2141

^* To whom correspondence should be addressed.

Received April 11, 2002

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Bimolecular oxygenation of tri-liganded R-state human hemoglobin (HbA) is described by bi-exponential kinetics with association rate constants k_alpha = 27.2 ± 1.3 (µM*sec)^-1 and k_beta = 62.9 ± 1.6 (µM*sec)^-1. Both the observed processes have been assigned to the bimolecular oxygenation of alpha- and beta-subunits of the native tetrameric protein by molecular oxygen. The quantum yields of photodissociation within the completely oxygenated R-state HbA are gamma_alpha = 0.0120 ± 0.0017 and gamma_beta = 0.044 ± 0.005 for alpha- and beta-subunits, respectively. The oxygenation reactions of isolated alpha^PCMB- and beta^PCMB-hemoglobin chains are described by mono-exponential kinetics with the association rate constants k_alpha = 44 ± 2 (µM*sec)^-1 and k_beta = 51 ± 1 (µM*sec)^-1, respectively. The quantum yields of photodissociation of isolated alpha^PCMB- and beta^PCMB-chains (0.056 ± 0.006 and 0.065 ± 0.006, respectively) are greater than that observed for appropriate subunits within the R-state of oxygenated HbA.

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KEY WORDS: human hemoglobin, oxyhemoglobin, alpha- and beta-subunits, molecular oxygen, kinetic absorption spectroscopy, oxygenation, bimolecular reaction, rate constant

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