Influence of steric factors on oxygen binding. I. Studies on 2,4-diisopropyldeuteroheme-myoglobin.
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.
D000818:Animals; D003905:Deuteroporphyrins; D006418:Heme / Q000031:analogs & derivatives; D006427:Hemin / Q000031:analogs & derivatives; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008786:Metmyoglobin; D009211:Myoglobin; D010084:Oxidation-Reduction; D010100:Oxygen; D010313:Partial Pressure; D011166:Porphyrins; D011485:Protein Binding; D013053:Spectrophotometry; D014907:Whales
D003905:Deuteroporphyrins; D009211:Myoglobin; D011166:Porphyrins; D008786:Metmyoglobin; D006418:Heme; D006427:Hemin; D010100:Oxygen