Xanthoprotein Test
Historical document, translated for reference. It reflects medical knowledge of the 1920s–30s and is not medical advice.
Summary
The xanthoprotein test, also known as Mulder's reaction, is a color test for proteins that detects aromatic amino acids like tyrosine and tryptophan. The test involves adding concentrated nitric acid to the substance, heating to form a yellow color, and then adding ammonia to produce an orange color.
Encyclopedia entry (1928–1936)
XANTHOPROTEIN TEST, or Mulder's reaction, a color test for proteins, caused by the presence in them of aromatic (mainly tyrosine) and certain heterocyclic (tryptophan) groups. To the substance being tested, concentrated HNO3 is added until precipitation ceases; upon heating, the precipitate turns yellow and dissolves, giving the liquid a yellow color; after cooling, an excess of ammonia or caustic alkali is added; the color becomes orange. The reaction is caused by the formation of yellow-colored nitro compounds (for example, nitrotyrosine from tyrosine). This reaction is responsible for the yellow coloring of skin moistened with strong HNO3. For detecting protein in urine, this reaction is unsuitable due to the yellow color of the urine itself. In recent years, the xanthoprotein test has also been used for the quantitative determination of tyrosine and tryptophan in proteins.
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Cite this page
“Xanthoprotein Test.” Soviet Medical Encyclopedia. English translation of Bolshaya Meditsinskaya Entsiklopediya, 1st ed. (Moscow, 1928–1936), ed. N. A. Semashko. https://sovietmedicalencyclopedia.pages.dev/article/xanthoprotein-test/