Spectrophotometric determination of tryptophan in intact proteins by the acid ninhydrin method

Ibolya Molnár-Perl, Margit Pintér-Szakács

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24 Citations (Scopus)


The interaction of tryptophan, lysozyme and tyrosine with ninhydrin in strong acid media has been investigated at 20, 25, 30, and 35°C by spectrophotometry. Second-order rate constants and molar absorptivity values have been evaluated from an analytical point of view. Optimum conditions for the selective estimation of tryptophan, tryptophan residues in intact proteins, and indoles-without the disturbing affect of tyrosine-have been given. Under optimum conditions, in the concentration range from 2.5 × 10-8 to 3.0 × 10-7m, molar absorptivity values and reproducibility data for various reactants have been reported. Molar absorptivity values (Am × 10-3/m × cm) of tryptophan (21.35), lysozyme (19.33), bovine serum albumin (21.05), human serum albumin (21.00), casein (17.85), α-chymotrypsin (18.28), trypsin (14.43), indole (5.03), and indole-3-acetic acid (13.75) have been measured with a standard error of 2.3% or less for any particular reactant.

Original languageEnglish
Pages (from-to)16-19
Number of pages4
JournalAnalytical Biochemistry
Issue number1
Publication statusPublished - Feb 15 1989

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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