Photometric Microdetermination of Total Serum Globulins by Means of a Tryptophan Reaction

Abstract

Abstract The Tauber perchloric acid method and the Fischl colorimetric procedure were combined into a quantitative method for tryptophan that is applicable directly to proteins without hydrolysis. The colorimetric tryptophan method was compared with both salt fractionation and electrophoretic methods for 26 normal sera and those from 51 patients with various chronic diseases. Analysis of the results for total serum globulins and A/G ratio in the three procedures indicated good agreement. Since serum globulins increase in diseases involving disturbed protein metabolism, accuracy of the determination increases as the disease progresses, whereas that for serum albumin falls. The tryptophan reaction is also directly applicable to low-protein fluids such as urine or cerebrospinal fluid, where salt fractionation technics are not suitable for determination of the A/G ratio. We confirmed Brackenridge's finding that increase in tryptophan content of malignant sera is due to increased total serum globulin level and not to increased tryptophan incorporation into a particular protein fraction.