Interaction Of Myoglobin Research Articles

Interactions of myoglobin with urea and some alkylureas: II. Calorimetric and circular dichroic studies

The interactions of myoglobin with urea, methyl-, N, N′-dimethyl- and ethylurea were studied by means of calorimetry and circular dichroism (CD). The enthalpies of transfer from water to aqueous denaturant solutions are positive for the alkylureas and negative for urea. The difference is due to the presence of hydrophobic groups in the alkylureas. Gibbs free energies of transfer for urea solutions were obtained from preferential binding data determined previously. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions between protein and denaturant. Analysis of the far-ultraviolet CD spectra reveals some differences in the denaturing activity of urea and the alkylureas, the latter being stronger denaturants than urea. Myoglobin displays relatively high stability towards these denaturants since concentrations above 5 M are needed for achieving major conformational changes.

Interactions of myoglobin with urea and some Alkylureas: I. Solvation in urea and Alkylurea solutions

The interactions of myoglobin with urea, methyl-, N, N′-dimethyl- and ethylurea in aqueous solutions were studied by density measurements. From the densities at constant chemical potential and constant morality, the partial specific volumes of myoglobin in these solutions as well as the extent of preferential binding of urea and alkylurea to myoglobin were determined. It has been found that water and not the denaturant is preferentially bound in urea solutions and alkylurea solutions up to 4M so that the Gibbs free energy of myoglobin, i.e., its chemical potential in a denaturant solution, is larger than in water. This behavior of myoglobin is different from that of other globular proteins for which preferential binding of urea has been found. It appears that preferential hydration of myoglobin is due to its high content of ionic groups.

Interaction of Myoglobin and Cytochrome c

Spectrophotometric studies of various mixtures of reduced and oxidized forms of myoglobin and cytochrome c revealed that oxymyoglobin is capable of reducing ferricytochrome c at a molar ratio of 1. Other combinations, i.e. oxymyoglobin and ferrocytochrome c; metmyoglobin and ferricytochrome c; or metmyoglobin and ferrocytochrome c showed no spectral change during the time course studied. The pH optimum of the reaction was found to be 7.2. The Q10 was about 5 and the activation energy was about 29 kcal per mole. Aging of oxymyoglobin tended to increase the rate of the reaction, but metmyoglobin added to the reaction mixture had no effect on the system. Antimycin A, amytal, and rotenone were without effect on the reaction. The partial carboxymethylation of histidyl residues of myoglobin increased the reaction rate to twice that of the control. The formation of a complex between oxymyoglobin and cytochrome c was not detected by various physical methods. Oxygen had an inhibitory effect on the reaction of the oxymyoglobin-ferricytochrome c system. This suggested that deoxymyoglobin rather than oxymyoglobin is the reacting species and that the rate-limiting step is the dissociation of oxygen from oxymyoglobin. This was confirmed by measurements showing that deoxymyoglobin reacted with ferricytochrome c at rates significantly greater than those of oxymyoglobin-cytochrome c system. This reaction was shown to proceed in stoichiometric fashion under equilibrium conditions. Carbon monoxide myoglobin was unreactive.

The interaction of myoglobin with mitochondrial structural protein.

The interaction of myoglobin with mitochondrial structural protein.