Overtone proteins

Overton, M. C. and Blumer, K. J. (2000). G-protein-coupled receptors function as oligomers in vivo. Curr. Biol. 10, 341-4. 

However, any vibrating system not only has a natural vibration frequency but will also vibrate at twice that frequency, which is known as the first overtone. The first overtone of the vibrations of molecules like water, proteins and fats correspond to a frequency in the near-infrared. Because these frequencies are overtones all of the spectroscopic problems that preclude making quantitative measurements in the mid-infrared are not present in the near-infrared. 

It has been observed that for some proteins the room temperature phosphorescence lifetimes are increased in D20. The phosphorescence lifetime of liver alcohol dehydrogenase is 300 ms in H2Oand 500 ms in D2O.<10) Phosphorescence lifetimes are often dramatically increased by exchanging hydrogen with deuterium. The reason for this is that decay rates are affected by overtones of the C-H or N-H stretch. In the case of tryptophan in... 

The chemistry of cluster complexes, e.g. of the sort [FeitSi, (SR) i,] 2, is of particular interest since such complexes are known to be close representations or synthetic analogues of the redox centres present in various iron-sulphur proteins. It is important to know whether the valence electrons are localized or delocalized in such complexes - in fact several studies by e.s.r., n.m.r., and, more recently, resonance Raman spectroscopy have shown that such clusters are delocalized rather than trapped-valence species. This result is linked with the most important biophysical property of iron-sulphur proteins, viz. that of electron transfer. Rapid electron transfer is possible if any consequential geometric rearrangements around the metal atom sites are small, as implied by many resonance Raman results on such cluster complexes (cf. the small-displacement approximation, which provides a basis for enhancement to fundamental but not to overtone bands) (22). Initial studies of [MSi,]2- ions (M = Mo or W) (23,24) have since been supplemented by studies of dinuclear species e.g. [(PhS)2FeS2MS2]2 (25) and cluster species... 

Twyman SJ, Overton J, Rowe DJ (2000) Measurement of urinary retinol binding protein by immunonephelometry. Clin Chim Acta 297 155-161... 

Based on the earlier work of Meyer and Overton, who showed that the narcotic effect of anesthetics was related to their oil/water partition coefficients, Hansch and his co-workers have demonstrated unequivocally the importance of hydrophobic parameters such as log P (where P is, usually, the octanol/water partition coefficient) in QSAR analysis.28 The so-called classical QSAR approach, pioneered by Hansch, involves stepwise multiple regression analysis (MRA) in the generation of activity correlations with structural descriptors, such as physicochemical parameters (log P, molar refractivity, etc.) or substituent constants such as ir, a, and Es (where these represent hydrophobic, electronic, and steric effects, respectively). The Hansch approach has been very successful in accurately predicting effects in many biological systems, some of which have been subsequently rationalized by inspection of the three-dimensional structures of receptor proteins.28 The use of log P (and its associated substituent parameter, tr) is very important in toxicity,29-32 as well as in other forms of bioactivity, because of the role of hydrophobicity in molecular transport across cell membranes and other biological barriers. 

Floyd, D. H., Geva, A., Bruinsma, S. P., Overton, M. C., Blumer, K.J., and Baranski, T. J. (2003). C5a receptor oligomerization. II. Fluorescence resonance energy transfer studies of a human G protein-coupled receptor expressed in yeast. J. Biol. Chem. 278, 35354-35361. 

Chen, W.J., Moomaw, J.F., Overton, L., Kost, T.A., and Casey, P.J. (1993). High level expression of mammalian protein farnesyltransferase in a baculovirus system. The purified protein contains zinc. J Biol Chem 268 9675-9680. 

All the higher (1st through 6th) overtones of the 0-H, N-H, C-H, and S-H bands from the IR are seen in the(much smaller) NIR region. This, in addition to combination bands (e.g., C=0 stretch + N-H bend in protein), gives rise to a crowded spectrum with severely overlapping bands. 

Some of the difficulties experienced when developing spectroscopic techniques to replace traditional wet chemistry have related to the correlation of measurements, despite the intrinsic difference in their origin. Shenk and colleagues [3] discussed this issue in the context of NIR spectroscopy. For example, measurements of protein based on total nitrogen content are not directly equivalent to a spectroscopic approach that only probes the N—H bonds. Similarly, determining individual fatty acids from the fairly broad combination and even broader overtone bands found in the NIR region, is hardly related to the quantification of species isolated on the basis on chain length and level of saturation. 

The absorption intensity of the 0-1 vibronic sideband is entirely borrowed by HT coupling. The observation that this 0-1 transition is of comparable intensity to the 0-0 transition suggests the feasibility of resonance Raman processes in which both the absorption and emission moments are borrowed. This second-order HT coupling displays itself in the appearance of first overtones and combination bands of non-totally symmetric modes. These are observed extensively in the haem proteins 35). 

Fig. 10.34 shows the INS spectrum of ox femur as the organic component is progressively removed [83]. Fig. 10.34a is very similar to that of the protein Staphylococcal nuclease. Fig 10.32, and emphasises one of the problems of working in this field because proteins are largely made of the same monomers (amino acids), the INS spectra of very different proteins tend to look very similar. Removal of the fat results in little change in the spectrum, Fig. 10.34b. It can be seen that elimination of the protein is highly effective, Fig. 10.34c the C-H stretching modes just below 3000 cm" and the C-H deformation modes at 1200-1500 cm have both disappeared. There is a weak, broad peak at 630 cm and its overtone near 1300 cm. For comparison, the INS spectrum of a highly crystalline reference hydroxyapatite is shown in Fig. 10.34d. The frequency match of the of the residual bone peak and that of the hydroxyapatite is exact, the width of the peak is attributed to heterogeneous broadening. The spectrum demonstrates that hydroxyl groups are still present in bone.

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