OXYGEN BINDING TO MYOGLOBINS AND THEIR COBALT ANALOGS

Thermodynamic measurements for O2 binding to native myoglobins and their cobalt analogues are discussed for proteins from three aquatic mammals: sperm whale, grey whale, and sea lion; reference is also made to studies on horse myoglobin. Emphasis is placed on the differences between O2 binding by the Fe and Co forms of the same protein. By comparing these differences within the set of myoglobins, and between proteins and the Fe and Co “picket-fence” porphyrin models of Collman et al., we are able to draw inferences that would be impossible with, say, the direct comparison of myoglobin and the Fe-por-phyrin model, or Co-myoglobin and the Co-porphyrin model. In particular, such comparisons confirm the fact that the cobalt-substituted myoglobins are true analogues of the natural proteins. They also suggest that there can be significant differences between oxygen binding in the proteins and the porphyrin models: similar affinities are achieved by different enthalpy-entropy compensation effects. © 1979, American Chemical Society. All rights reserved.