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Influence of steric factors on oxygen binding. I. Studies on 2,4-diisopropyldeuteroheme-myoglobin.

H Ogoshi·K Kawabe·S Mitachi·Z I Yoshida·K Imai·I Tyuma
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Abstract

Sperm whale apomyoglobin was recombined with 2,4-diisopropyldeuterohemin to form 2,4-diisopropyldeuteroheme-myoglobin and its various physico-chemical properties were investigated to get an insight into the structural and functional role of the peripheral vinyl groups. 2,4-Diisopropyldeuteroheme-myoglobin showed a four times lower oxygen affinity at 25 degrees C and larger enthalpy and entropy changes of oxygenation than the corresponding values of native myoglobin. 2,4-Diisopropyldeuteroheme-metmyoglobin shows a pKa value of 9.68 which is higher than those of native metmyoglobin and mesoheme-metmyoglobin. The rate of autooxidation of oxy-form was about seven times larger in 2,4-diisopropyldeuteroheme-myoglobin than in native myoglobin. The electron-donating effect of isopropyl groups does not give straightforward explanation for these anomalous properties of 2,4-diisopropyldeuteroheme-myoglobin. It is proposed that site and stereospecific van der Waals' interaction between the polypeptide side chains and the peripheral 2,4-diisopropyl groups may weaken the interaction between the bound oxygen molecule and the distal His, resulting in the decrease in the stability of oxyform.

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AnimalsDeuteroporphyrinsHemeHeminHydrogen-Ion ConcentrationKineticsMetmyoglobinMyoglobinOxidation-ReductionOxygenPartial PressurePorphyrinsProtein BindingSpectrophotometryWhalesJournal Article

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H Ogoshi, K Kawabe, S Mitachi, Z I Yoshida, K Imai, I Tyuma. 1979-12-14. Influence of steric factors on oxygen binding. I. Studies on 2,4-diisopropyldeuteroheme-myoglobin.. https://doi.org/10.1016/0005-2795(79)90246-0

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