A COMPARISON OF METHODS FOR DETERMINING TOTAL-BODY PROTEIN

The aim of the study was to find the optimal method (with respect to c onvenience and accuracy) for determining total protein in whole-body h omogenates of rats. Three different protein extraction methods and fiv e different protein concentration methods were assessed. The results w ere compared against a reference value measured by complete amino acid analysis after acid hydrolysis. The data demonstrated that extraction with 5% (w/v) sodium dodecylsulfate (SDS) in 0.5 N NaOH was far super ior to that with water alone or to 6 N guanidine-HCl. A comparison of the Biuret, Bradford, and bicinchoninic acid methods on the SDS-NaOH-e xtracted samples showed that the Biuret method was optimal, giving a v alue that was 90% of the reference value with a small variation (2.4% of the mean). The Kjeldahl method gave the correct protein concentrati on only when a nitrogen factor of 5.51 +/- 0.03 (N = 5) was applied, T he results suggest that extraction with SDS-NaOH followed by the Biure t procedure is a good method for measuring protein concentrations in w hole body rat homogenates. (C) 1995 AcademicPress,Inc.