LowryMethode

The Lowry method is a colorimetric protein assay used to quantify protein concentration in a sample. It was developed by Oliver H. Lowry and colleagues in 1951 and remains one of the historically prominent protein assays in biochemistry.

Principle: The assay combines a Biuret-type reaction with the Folin-Ciocalteu phenol reagent. In alkaline conditions, peptide bonds reduce copper(II) ions to copper(I), forming a complex with reduced copper. This reduction, in turn, reduces the Folin-Ciocalteu reagent, producing a blue color whose intensity is proportional to the protein amount present. The absorbance is typically measured at around 750 nm, and a standard curve is prepared using a known protein, commonly bovine serum albumin (BSA).

Procedure and reagents: A typical protocol uses copper sulfate, sodium potassium tartrate, and sodium carbonate to create the alkaline copper solution, plus the Folin-Ciocalteu reagent for color development. Samples and standards are treated with the reagent mix, incubated for a defined period, and the resulting blue color is measured spectrophotometrically. The exact timings and reagent concentrations can vary between protocols and commercial kits.

Advantages, limitations, and alternatives: The Lowry method offers good sensitivity and a wide dynamic range compared with the Biuret method, but it is more time-consuming and can be influenced by interfering substances. Reducing agents (such as DTT or β-mercaptoethanol), certain detergents, and high concentrations of salts can affect results. Variants and modifications have been developed to improve compatibility with some sample types.

Applications: It is used for estimating protein concentration in biological samples, tissue lysates, purified protein preparations, and other solutions where accurate protein quantification is required.