Optical rotatory dispersion of sperm whale ferrimyoglobin and horse ferrihemoglobin

Dielectric dispersion in aqueous solutions of oxyhaemoglobin and carboxyhaemoglobin

The relative permittivity and conductivity of aqueous solutions of oxyhaemoglobin and carboxyhaemoglobin were measured over the frequency range 150kHz-100MHz. To minimize errors of measurement the investigations were carried out with three different samples of each type of haemoglobin, independent apparatus being used in two different laboratories. The dielectric increment and relaxation time were calculated at each of several temperatures from the results. These lead to a dipole moment of 400 Debyes and an activation enthalpy of 17.6+/-1.4kJ.mol(-1), both of which were found to be independent of temperature to within experimental error over the range 3-35 degrees C. The value of the dipole moment shows that the distribution of charge throughout the haemoglobin molecule is nearly symmetrical with respect to the centre of charge. The magnitude of the activation enthalpy is similar to that of the viscosity of water, in accord with the common observation that dielectric relaxation and viscosity are related phenomena. No significant differences are found between the dielectric parameters of oxyhaemoglobin and carboxyhaemoglobin. Combining the results with those obtained from X-ray diffraction of the solid a hydration value of 0.45g of water/g of protein is suggested, subject to the limitations of the model used. Finally, the results indicate the presence of a subsidiary dispersion, which could be attributed to the above quantity of bound water having a static permittivity of about 100 and a relaxation frequency in the region 100-200MHz.

Structural stability and solvent denaturation of myoglobin

As judged from the midpoints of the denaturation transition of 31 water-miscible alcohols, ureas, and amides, the effectiveness of these denaturing agents on sperm-whale myoglobin increases with increasing chain length and hydrocarbon content, as expected in view of the disorganization of the hydrophobic interior of this protein. Increase in the hydroxyl content, blocking of the functional amino groups of the ureas and amides by alkyl substitution, and branching of the hydrocarbon portion of the denaturants are of less importance in determining the effectiveness of the denaturants.

Circular dichroism of biological macromolecules

Circular dichroism, the unequal absorption of right and left circularly polarized light, is a manifestation of optical activity in the vicinity of absorption bands. To the experimental scientist interested in the conformation of macromolecules and in the sensitive response of optical activity to conformational alteration, it offers a relatively new and powerful means of understanding the environment of chromophoric residues. As a tool in the elucidation of electronic spectra, it should be useful to the theoretical scientist in identifying weakly allowed absorption bands as well as in providing rotational parameters which can be compared with the developing theory of optical activity. I have stressed application of circular dichroism, to experimental aspects of protein and nucleic acid conformation in solution. Much is still uncertain in particular quantitative details. However, even these early results shed new light and yield new information on the conformation of these molecules.

Conformational changes and the regulation of glutamate-dehydrogenase activity

1. The effect of NADH and the non-competitive inhibitor GTP on the optical-rotatory-dispersion properties of glutamate dehydrogenase has been studied. 2. Analysis of the data in terms of the a(0) and b(0) parameters of the Moffitt-Yang equation indicates that a conformational change is induced either by NADH or by GTP in the presence of small amounts of NADH. 3. Sedimentation measurements under comparable conditions showed that the enzyme reversibly dissociates into sub-units but that this dissociation is only secondary to the conformational changes. 4. Fluorescence measurements showed that the binding constant of NADH and the number of binding sites on the enzyme increased in the presence of GTP. 5. This is confirmed by studies of fluorescence polarization, which in addition showed that the movement of NADH on the enzyme surface is more restricted in the presence of GTP. 6. The relation of these results to possible regulatory mechanisms is discussed.