Diagnosis of head and neck squamous cell carcinoma using Raman spectroscopy: tongue tissues

Raman spectroscopy is a powerful optical technique capable of providing the structural information at the molecular level. Thus, the technique can be used to detect biochemical changes associated with carcinogenesis and identify the biomolecules involved in cancer. We studied the Raman spectral characteristics of normal, carcinoma in situ, and invasive squamous cell carcinoma (SCC) tissues of tongue, and identified the spectral features that can discriminate these three tissue types. We found that the intensities of Raman bands assignable to tryptophan increase while those attributable to protein keratin decrease when tissue changes from normal to invasive SCC. The variation observed in the intensity of many discriminating peaks including those of tryptophan and keratin as tissue changes from normal to carcinoma in situ and then to invasive SCC suggests that Raman spectroscopy can be used to monitor progression of the disease. We have also analyzed the data with multivariate statistical methods such as principal component analysis and discriminant function analysis. These chemometric methods clearly separate the whole data into three distinct groups consistent with results of pathology. We were able to detect with 91% success rate the normal and carcinoma in situ tissues and with 89% accuracy the invasive SCC tissues of the tongue. Copyright © 2011 John Wiley & Sons, Ltd.     

Static and Dynamic Quenching of Tryptophan Fluorescence in Various Proteins by a Chromium (III) Complex

The interaction of a chromium (III) complex, (R,R)-N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diaminochromium (III), with human serum albumin, bovine serum albumin, lysozyme, and free tryptophan was studied using steady-state fluorescence spectroscopy. Dynamic and static quenching constants were calculated using Stern-Volmer kinetics. The complex bound more tightly to the serum albumins than to lysozyme or free tryptophan, but only one binding site was determined in all systems. The interaction was also determined to be thermodynamically favorable, and the binding constants were on the order of 10³–10⁶. The fluorescence quenching was static in nature with Forster distances in the 1.8–2.0 nm range.     

Zeolite-Modified Carbon-Paste Electrode as a Selective Voltammetric Sensor for Detection of Tryptophan in Pharmaceutical Preparations

Abstract

Several synthetic zeolites such as mazzite, mordenite, zeolite L, zeolite beta, and MCM-41 were tested as electrode modifiers in voltammetric determination of tryptophan. It was found that addition of zeolite beta to the carbon paste would generate the peak current of Trp because of its catalytic effect. The anodic peak currents were proportional to Trp concentrations in the range of 5.0 × 10^?7 to 5.0 × 10^?3 M. The detection limit was 1.0 × 10^?7 M. The influence of several species, especially other amino acids, were tested. The proposed method was applied successfully to the determination of tryptophan in pharmaceutical formulations.     

Effects of sequence context on the binding of tryptophan-containing peptides by the cucurbit[8]uril–methyl viologen complex

This paper describes a novel assay for measuring the relative extent of peptide binding in a large parallel format and the use of this assay to explore the effects of sequence context on the binding of tryptophan (Trp)-containing peptides by the synthetic receptor comprising the noncovalent complex between cucurbit[8]uril and methyl viologen (i.e. Q8√MV). The extent of quenching of Trp fluorescence upon binding to Q8√MV was used to measure the relative extent of binding and thus the relative affinities of 104 Trp-containing peptides, in parallel, using a fluorescence plate reader. This study resulted in the remarkable observation that the identity of the amino acid residues at positions adjacent to the Trp-binding site has little if any influence on the binding affinity. This finding suggests that Q8√MV should be effective for the recognition of Trp residues within a broad range of peptide sequences.     

Dipolar Relaxation Times of Tryptophan and Tyrosine in Glycerol and in Proteins: A Direct Evaluation from Their Fluorescence Decays

The dipolar relaxation process induced around tryptophan, indole and tyrosine in viscous media, as well as in several single tryptophan-containing proteins (staphylococcal nuclease, ribonuclease T1, melittin and albumin), has been studied by dynamic fluorescence measurements. A new theoretical model has been developed, including the relaxation dynamics directly in the fluorescence decay function. The phase shift and demodulation data have been fitted with this new algorithm which allows to resolve the different relaxation times influencing the fluorophore excited state. These parameters are in a good agreement with those measured with the traditional time-resolved emission spectroscopy. The results indicate that indeed a correlation exists between the radiative rate change obtained with the new model and the temporal spectral shift reported in the literature. Finally, this new approach has also been extended to the case of superoxide dismutase and phosphofructokinase, allowing to measure the relaxation time even in proteins lacking a temporal spectral shift during the fluorphore's lifetime.     

Efficiency of energy transfer by resonance in quenching of protein fluorescence by dyes

Considering the quenching of tryptophan fluorescence of bovine serum albumin by various dyes as an example, it is shown that overlap of radiation and absorption spectra does not necessarily lead to energy transfer by resonance. No correlation is revealed between the limiting quenching and the Forster overlap integral. Quenching can occur even in the absence of overlap. The magnitude of energy transfer is markedly lower than that of quenching owing to competing processes, namely, excitation deactivation by the dye and, probably, by the protein itself which undergoes conformation upon sorption of the dye. Negatively charged and neutral dyes posses, on the average, a higher quenching activity relative to albumin than do positively charged dyes. Institute of the Biophysics of Cells of the Russian Academy of Sciences, Pushchino, 142292, Moscow Region, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 290–293, March–April, 1998.     

黄素为辅基的色氨酸卤化酶及其在生物合成色氨酸衍生物中的应用

黄素为辅基的色氨酸卤化酶在催化合成有机氯化物和溴化物过程中的起着非常重要的作用。在这篇论文我们将阐述一种通过在假单胞菌株中表达外源色氨酸卤化酶基因来催化合成3-（2-氨基-4-氯苯基）吡咯的新组合生物合成方法——组合培育法。3-（2-氨基-4-氯苯基）吡咯是分析和诱导性基因突变硝吡咯菌素生物合成途径的重要中间产物。研究表明，这种新的组合培育法可以用于改变和分析一些重要的二级代谢途径。