Studies of myosin and its proteolytic fragments by laser Raman spectroscopy

Two bands in the Raman spectrum of myosin, at 1,304 cm-1 and 1,270 cm-1, are attributable to alpha-helical structure. The first of these, also present in the spectrum of light meromyosin (LMM) but not in that of subfragment-1 (S-1), is assigned to the coiled-coil tail region of myosin; the second, seen in spectra of S-1 or heavy meromyosin (HMM), is largely absent from the spectrum of light meromyosin and is likely to correspond to the alpha-helical segments of the head region. When myosin or LMM aggregates, spectral bands attributable to backbone and sidechain groups sharpen suggesting a reduction in motional freedom. This sharpening is particularly apparent in the 902 cm-1 C--C stretching mode. Mg2+ broadens and shifts the peak at 1,244 cm-1 to 1,237 cm-1 and diminishes the intensity from 1,230 to 1,240 cm-1, changes which appear to be associated the S-1 region. MgPPi produces changes in the 1,300 cm-1 region attributable to alpha-helical regions in coiled-coil structures suggesting that MgPPi affects not only S-1, but also some part of the myosin rod.

A laser Raman spectroscopic study of Ca2+ binding to troponin C

Laser Raman spectroscopy has been used detect structural changes in troponin C induced by Ca2+ binding. Addition of Ca2+ - Mg2+ sites produces perturbations in the amide III region of the spectrum indicative of increased alpha-helical content, and in regions of the spectrum corresponding to carboxylate, thiol, and phenol side chains. However, Ca2+ binding to the low affinity Ca2+ - specific sites is not detected by laser Raman spectral changes.

Nonequilibrium linear behavior of biological systems. Existence of enzyme-mediated multidimensional inflection points

The linear phenomenological equations of nonequilibrium thermodynamics are limited theoretically to near equilibrium although a number of biological systems have been shown to exhibit a "linear" relationship between steady-state flows and conjugate thermodynamic forces outside the range of equilibrium. We have found a multidimensional inflection point which can exist well outside the range of equilibrium around with enzyme-catalyzed reactions exhibit "linear" behavior between the logarithm of reactant concentrations and enzyme catalyzed flows. A set of sufficient conditions has been derived which can be applied to any enzyme mechanism to determine whether a multidimensional inflection point exists. The conditions do not appear overly restrictive and may be satisfied by a large variety of coupled enzyme reactions. It is thus possible that the linearity observed in some biological systems may be explained in terms of enzyme operating near this multidimensional point.

Cyclo(L-prolylglycyl)3 and its sodium, potassium, and calcium ion complexes: a Raman spectroscopic study

Raman spectra of the cyclic hexapeptide cyclo-(L-prolylglycyl)3 and its Na+, K+, and Ca2+ complexes are reported for the solid state and for samples in solution. Model compounds and N-deuteration were used to aid mode identification. Spectra of the uncomplexed ionophore in solution are consistent with previously proposed solution conformations and permit the identification of spectral lines characteristic of proline-containing peptide bonds in the trans and the cis conformations. Upon cation complexation the prolyl carbonyl stretch bands sharpen and upshift 20-30 cm-1 (to 1690-1700 cm-1). The glycyl carbonyl stretch band is unaffected by Na+ complexation, upshifted approximately 15 cm-1 by K+ complexation, and downshifted approximately 20 cm-1 (to 1619 cm-1) by Ca2+ complexation. Arguments supporting the involvement of prolyl carbonyl groups in cation complexation are noted. Spectra of the Na+ complex of the tetramer cyclo(L-prolylglycyl)4 suggest an asymmetric structure.

A binding site model of membrane transport: binary and cooperative flows

The flows of solute molecules in a membrane under the influence of concentration gradients are considered within the framework of classical physical theories. A lattice model is constructed in which the binding sites represent potential minima and the flows are regarded as a result of molecules' making discrete transitions between the binding sites. Expressions for two-component currents are derived from certain descriptions for the transition mechanism. Where the molecular movement is given the crudest description, permeability coefficients are identical for both components and there is no current coupling. Where the molecular movement is given some finer detail, the permeability coefficients differ and positive coupling of flows appears. Our result applies to a combination of flows of tracer and abundant species as well as, more generally, to any combination of flows of two components which are distinguishable yet kinetically similar. Also considered are binary currents whose transport mechanism is further controlled by allosteric cooperativity. Whether the cooperative control is short or long ranged, permeability coefficients and fluxes differ appreciably from those without cooperative control. Thus, unlike in the case of channel flow, current coupling here may be either positive or negative, depending on the strength and nature of cooperative coupling. Numerical evidence suggests that the permeability and coupling may have discontinuous behavior, possibly indicating the existence of phase transitions. Our lattice model, from which the formulations for the flows are obtained, is compatible with current concepts of membrane structure.

Raman spectroscopy: a structural probe of glycosaminoglycans

We report the first Raman spectroscopic study of the glycosaminoglycans chondroitin 4-sulfate, chondroitin 6-sulfate and hyaluronic acid, both in solution and in the solid state. To aid in spectral identification, infrared spectra were also recorded from films of these samples. Vibrational frequencies for important functional groups like the sulfate groups, glycosidic linkages, C-OH and the N-acetyl group can be identified from the Raman spectra. Certain differences in the spectra of the different glycosaminoglycans can be interpreted in terms of the geometry of the various substituents, while other differences can be related to differences in chemical composition.

Opsin structure probed by raman spectroscopy of photoreceptor membranes

The first nonresonance Raman spectra of photoreceptor membranes are presented. Information about the membrane protein, opsin, and the membrane phospholipids can be deduced. Opsin appears to contain alpha-helical structure but little beta structure. The tyrosine residues are predominantly hydrogen bonded, and disulfide bonds, if they are present, are not in the normal gauche-gauche configuration.

Laser raman spectroscopy--new probe of myosin substructure

Laser Raman spectroscopy is used to probe the heterogeneous substructure of the large contractile protein myosin. Some peaks are assigned to specific chemical groups of the molecule; others, notably the conformationally sensitive amide III vibrations, provide information on the structurally distinct regions of the molecule. Deuteration of the NH groups is instrumental in the assignment of these vibrational modes. The relative intensities of bands typical of alpha-helical conformations (near 1265 and 1304 cm-1) and bands associated with nonhelical structure (near 1244 cm-1) are sensitive indicators of myosin substructure and represent potentially useful probes of conformational changes.

Models of ionic transport in biological membranes. Raman spectroscopy as a probe of valinomycin, gramicidin A', and rhodopsin conformations

There is evidence that membrane proteins can serve as the functional units of ionic transport in biological membranes. Laser Raman spectroscopy has been used to probe specific molecular interactions inside two models of transport membrane proteins, valinomycin and gramicidin A. Conformational changes of these molecules, as well as specific interactions with ions, can be detected and may help elucidate how membrane transport proteins such as Na+ minus K+ ATPase and rhodopsin function. Resonance Raman spectroscopy has also been used to study conformational changes and protein-chromophore interactions in rhodopsin, the membrane protein that acts as the primary unit of visual excitation in the eye.

Raman spectroscopic investigation of gramicidin A' conformations

Gramicidin A' is believed to form transmembrane channels in lipid bilayers and biological membranes. The first Raman spectroscopic study of gramicidin A' is presented. Evidence is found for two types of conformation. One type is found in the powder and has a Raman spectrum similar to that of model polypeptides with beta hydrogen bonding. The second type is found when gramicidin A' is dissolved in dimethyl sulfoxide.

Raman spectroscopic evidence for two conformations of uncomplexed valinomycin in the solid state

Raman spectroscopy is applied for the first time to elucidate the different conformations of the carrier transport molecule, valinomycin. Splitting of the ester and amide carbonyl stretch vibrations is observed in the Raman spectrum of crystals of valinomycin grown from both n-octane and acetone. These observations support the contention that some ester carbonyl groups are intramolecularly hydrogen bonded. The Raman spectrum of valinomycin grown from o-dichlorobenzene does not display this feature.