Determination of total proteins in several tissues of rat: a comparative study among spectrophotometric methods

In the present paper, five spectrophotometric methods — biuret, Lowry modified by Hartree (Lowry/Hartree), p-chloranil, ultraviolet at 280 nm (UV-280 nm), and ultraviolet at 260/280 nm (UV-260/280 nm) — were used for protein determination in several rat tissues and the results were compared. The Lowry/Hartree method showed the highest sensitivity (0.9 μg/ml) and the biuret method the lowest sensitivity (55.7 μg/ml). The results were not statistically different for the following methods and tissues: Lowry/Hartree was compared to biuret for five tissues (adrenal, spleen, whole brain, liver and small intestine), to p-chloranil for two tissues (liver and epididymal fat pad), and to UV-260/280 nm for three tissues (whole brain, liver and pancreas). Since the Lowry/Hartree method needs a larger period of time for a whole assay to be carried out, we recommend for determination of total protein the following methods: UV-260/280 nm for whole brain, liver, and pancreas, p-chloranil for epididymal fat pad, and biuret for other tissues. We do not recommend the UV-280 nm method because there are many interfering substances in the tissues.