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The absorption of protein solutions in the UV is the result of tryptophan and tyrosine (and to a very minor, and negligible, extent phenylalanine and cysteine). The absorption maximum will depend on the pH of the solution, and spectrophotometric measurements are usually made in alkaline solutions. Absorption curves for tryptophan and tyrosine show that at …

The Isoelectric Point (pI) is the pH at which any given protein has an equal number of positive and negative charges, in other word the protein has no charge or neutral. At a pH below the isoelectric point, proteins carry a net positive charge, and above the Isoelectric Point protein has a net negative charge.

In order to quantitate protein in biological samples, these several methods, Bradford, Lowry, BCA, Bohlen, has limitation since the constituents of biological buffers sometimes interfere with those methods. Therefore, it is limiting their application. But don’t worry, there is still a method that could be used to estimate protein in biological samples. The method is …

Although Lowry method is not good enough compared to Bradford and Bicinchoninic Acid method for protein quantitation, but it is still widely used due to its acceptability to estimate protein in almost all circumstances in which protein mixtures or crude extracts are involved. Lowry method is based on the conversion of Cu2+ to Cu+ under …

Bradford method is a common colorimetric method to determine protein concentration in a sample solution. The Bradford method of protein determination is based on the binding of a dye, Coomasie Blue G, to the protein. This binding shifts the absorption maximum of the dye from red to blue. The absorbance of the solution is measured …

The Bicinchoninic acid (BCA) assay first was described by Smith, et al. BCA assay is similar to Lowry assay since it also depends on the conversion of Cu(2+) to Cu(+) under alkaline conditions. The Cu(+) is then detected by reaction with BCA. The reaction results in the development of an intense purple color with an …

It is possible to estimate protein concentration in a solution by using simple spectrometer. Absorption of radiation in the near UV (280 nm) by proteins depends on the Tyrosine and Tryptophan content (also to a very small extent on the amount of Phenylalanine and disulfide bond).