Introduction

The protein is a complex and biological molecule. Despite this complexity, there are many ways found to use proteins. For example, the collagen, the most abundant protein for humans and animals, is necessary for wound healing. The collagen can be associated with textile in hernia meshes. That’s why the quality of the mesh needs to be as good as possible and it starts by founding a way to quantify the protein to produce the mesh. The method of the biuret consists in a reaction between the peptide bonds of the protein and the copper (II) to form a blue-purple complex. The copper is present in a biuret reagent, under the shape of hydrated copper (II) sulfate, which contains sodium hydroxide, potassium sodium tartrate. The optical spectroscopy absorption is at 545nm. This method quantifies the entire protein and can use another protein for the standard range.

Experimental conditions

The standard range was made with a bovine serum albumin between 0 and 100 mg/mL. The stock solution had a concentration of 100mg/mL. Using a serial dilutions, concentrations of 50mg/mL, 25mg/mL and 12.5mg/mL were respectively prepared. Then, 1mL of each standard solution was mixed with 5mL of the biuret reagent. In order to prepare the blank, I mixed 1mL of water with 5mL of the biuret reagent. After 15mins of incubation, all the solutions were analyzed with the spectrophotometer at 545 nm.

Results

The line graph showed the absorbance according to the concentration of albumin. This absorbance took values between 0 and 0.45 and steadily increased with the concentration of bovine serum albumin between 0 and 100 mg/mL. This led to have a linear relation among those two parameters. The slope was 0.0045 mL/mg and the coefficient correlation was equal to 0.9994.

Conclusion

The biuret method leads to quantify a protein in a limited range because of the linear response. This method, used with the bovine serum albumin, brings about a systematic error. That’s why a correction factor results from this error. Therefore, this factor is the result of the nature of the protein which is quantify. It highlights the fact that a lot of work has to be done before using this method on any protein.

Curve showing the absorbance according to the concentration in bovine serum albumin at 545 nm between 0 and 100 mg/mL

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