Quantitative Determinations of Proteins

There are many proteins in the human body. A few hundreds of these compounds can be identified in urine. The qualitative determination of one or a series of proteins is performed by one of the electrophoresis techniques. Capillary electrophoresis can be automated and thus more quantified (Oda et al. 1997). Newer techniques also enable quantitative determination of proteins by gel electrophoresis (Wiedeman and Umbreit 1999). For quantitative determinations, the former method of decomposition into the constituent amino acids was followed by an automated spectropho-tometric measurement of the ninhydrin-amino add complex. Currently, a number of methods are available, induding spectrophotometry (Doumas and Peters 1997) and, most frequently, ELISAs. Small proteins can be detected by techniques such as electrophoresis, isoelectric focusing, and chromatography (Waller et al. 1989). These methods have the advantage of low detection limits. Sometimes, these methods have a lack of specifidty (cross-over reactions) and HPLC techniques are increasingly used to assess different proteins. The state-of-the-art of protein determination was mentioned by Walker (1996). 

Several useful methods for the quantitative determination of protein solutions were discussed in Chapter 2. Two of those methods, the Bradford protein assay and the direct spectrophotometric assay, will be applied to the a-lactalbumin solutions. Neither of these assays is specific for a certain type of protein rather they both estimate total protein content. 

El 9. Absorbance measurements of column fractions at 280 nm were used in this experiment to detect the presence of protein material. Do you think this method of analysis could lead to a quantitative determination of protein concentration What other biomolecules might interfere with this measurement ... 

Nagl S (2004) Quantitative determination of proteins on microarrays by time-resolved luminescent imaging. Diploma thesis, University of Regensburg... 

Nelson RW, McLean MA, Hutchens TW. Quantitative determination of proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Anal Chem 1994 66(9) 1408—1415. 

Chemical modifications of proteins have been carried out for a long time prior to any interest in the understanding of the chemical basis of the process. Early studies were motivated by the interest in quantitative determination of proteins and amino acids that conform its structure [104]. Intramolecular reactions occur naturally in posttranslational modifications such as disulfide bonding, glycosylation, or terminal residue cyclization. These modifications are relevant in structure-function relationships. They can produce conformational changes in order to switch between... 

To evaluate the useftilness of ATR-FTIR measurements for the quantitative determination of protein secondary structure, both PLS and classic curve-fitting analyses were performed. The results of these analyses are compared with values calculated from X-Ray structures in Table III. 

S. Kjellstrom, S. Lindberg, T. Laurell, G. Marko-Varga, Development of a push-pull microdialysis sampling technique for the quantitative determination of proteins, Chromatographia 52 (2000) 334. 

Stenberg E., Persson B., Roos H., and Urbaniczky C., Quantitative determination of protein with surface plasmon resonance by using radiolabelled proteins, J. Colloid Interfac. Sci., 143, 513-526, 1991. 

Nelson, R. W., et al. (1994). Quantitative Determination of Proteins by Matrix-assisted Laser-desorption Ionization Time-of-flight Mass Spectrometry, Anal Chem. 66 1408 1415. 

Quantitative determination of proteins is often needed to determine their concentrations and changes in cell growth and differentiation processes or in enzyme purification procedures. 

Historically, the quantitative determination of protein, particularly in the presence of large amounts of non-protein, was based on the estimation of the nitrogen content by the classical Kjeldahl method. Any other non-protein organic nitrogen was either assumed to be absent or was removed prior to analysis. The crude protein content was taken to be 6.25 times the % N found in the sample (this was based on the average N content of 16% in most proteins). 

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