Protein dipolar moment

It should be borne in mind, however, that enzyme proteins, like other proteins, are dipolar ionic structures surrounded by an intense electrostatic field. Horse carboxyhemoglobin, for example, has a dipole moment of 480 Debye units (molecular weight, 67,000). Compared with amino acids, sugars have a rather low dipole moment, due mainly to a considerable measure of mutual cancellation of the constituent link moments resulting from their disposition in space (glycine = 15, a- and... 

Observation of reorientational dynamics of dipolar groups surrounding the fluorophore in response to changes in the dipole moment of the fluorophore occurring upon electronic excitation. Such dynamics result in the appearance of spectral shifts with time,(1 ) in changes of fluorescence lifetime across the fluorescence spectrum,(7,32) and in a decrease in the observable effects of selective red-edge excitation.(1,24 33 34) The studies of these processes yield a very important parameter which characterizes dynamics in proteins— the reorientational dipolar relaxation time, xR. 

A development in the theory of nuclear relaxation in macromolecules by paramagnetic ions has been suggested by Gueron. (675) In the case of heme proteins there is a net polarization of the iron electronic spin magnetic moment which is oriented along the direction of the magnetic field. Modulation of this dipolar field due to the spin polarization (Curie spin) by rotational diffusion introduces an additional term into the expression for transverse relaxation [equation (18)] giving ... 

Integral proteins could provide a large contribution to the curvature-induced membrane polarization. Both dipolar and quadrupolar contributions could show up, more pronounced than those of lipids. The reason for such an expectation is the very large dipole moment measured for some proteins. Theory also demonstrates that such big molecules with no spherical symmetry may have a very large anisotropy of the quadrupole moment. 

Effect of One Dipolar Ion on the Solubility of Another Not only salts, but other dipolar ions, can increase ilie solubility of amino acids and proteins. The solubility of cystine, for example, is in creased by the addition of glycine to the solvent glycylglycine, with its higher dipole moment, has a markedly greater effect than glycine. On the other hand, the solvent action of a series of a amino acids decreases in the order glycine, alanine, aminobutyric acid, valine. Thus increase in the size of the non-polar side chain has the opposite effect from increase of dipole moment (Cohn, MoMeekin, Ferry and Blanchard, 42 and ref. 39, Chapter 10). 

Amino acids contain two functional groups amino -NH2 and carboxyl -COOH. Amino groups are basic while the carboxylic groups are acidic. Physiologically they exist as dipolar ions commonly called as Zwitter Ions (Fig. 12). The NH2 -CHR-C00 amino acid dipole is associated with a large dipole moment. Thus, aU protein molecules are dipolar in nature a property that is used extensively to separate proteins. 

Many covalent bonds have dipoles and dipole moments within dmg molecules are important for their interaction with the biomolecules within cells which transmit the dmg s action. The larger the dipole, the stronger the dipolar interaction with proteins and receptors within the cell. In addition, the strength of the dipole moment gives an indication of how likely the dmg is to be degraded by reactants with an affinity for positive or negative charge. As indicated above, in most cases dmg action is not based on covalent bond formation. There... 

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