Spectrophotometric studies of the isobestic points of hemoglobin derivatives of frog, Rana tigrina and toad, Bufo melanostictus: molecular adaptations to environment

Kanchan Kumari & R. C. Sinha*
Centre for Environment and Nature Conservation
Deptt. of Zoology, Patna university, Patna – 800005
Received 11th December, 2010; Revised 15th February, 2011

Abstract : Based on the isobestic points, oxygen saturation of hemoglobin of the frog, Rana tigrina, a semi-aquatic species and toad, Bufo melanostictus, a terrestrial species by differential spectrophotometry have been made. The hemoglobin content and the blood oxygen capacity (BOC) of both the animals have also been investigated. The results show that the hemoglobin concentration and the BOC of the frog are higher than that of the toad but the oxygen saturation is almost similar. The visible spectra of oxyhemoglobin and deoxyhemoglobin along with their absorptivities show that the absorption bands are different for HbO₂ and Hb. In case of the frog HbO₂ there are 2 peaks at λ_574.5 and λ_541.5 and that of the toad at λ₅₇₆ and λ₅₄₁. But there is only one peak in deoxyhemoglobin of the frog at λ₅₅₅ and toad λ₅₅₆. From the spectral band and absorptivities of HbO₂ and Hb isobestic points have been determined and therefrom oxygen saturation have been calculated and compared with that of the human adult. There are several invariant amino acid sequences from fish to man and therefore are fundamental to the function of the molecule. In the present study, the frog ortholog is most similar to toad hemoglobin suggesting most evolutionary related than fish and man. The molecular strategies for oxygen transport based on the sequence of amino acid leading to the conformational changes in the hemoglobin molecule along with their effectors in the frog and toad in light of their different habit and habitat have also been explored. The physiological significance of these observations is discussed herein for the first time.

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