| Abstract: | A more simple and sensitive assay for the quantitative determination of tyrosine in blood plasma is developed on the basis of a modification of the method of S. Udenfriend (1962). A volume of 0.2 ml of plasma is used in the analysis; after its deproteinization with trichloroacetic acid, it is reacted with sodium nitride, nitrous acid, and 1-nitroso-2-naphthol at 65°C, and the content of the reaction product is measured by the fluorescence at λex/λem=460/570 nm. The consumption of plasma and reagents is reduced by a factor of 5–10 compared to the original method; in addition, the stage of extraction with an organic solvent is excluded. The linear dependence of the fluorescence signal on the tyrosine concentration within the range of 2–60 μg/ml, high specificity, accuracy, and reproducibility of the assay are shown. The importance of tyrosine determination in monitoring of glucocorticoid therapy and protein catabolism is discussed. Institute of Photobiology, National Academy of Sciences of Belarus, 27, Akademicheskaya St., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 366–371, May–June, 1998. |
