HPLC study of tyrosinase inhibition by thiopronine

A. M. Girelli, E. Mattei, A. Messina

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Thiopronine (N-2-mercaptopropionyl-glycine, NMPG) inhibits the o-dihydroxy-phenolase activities of mushroom tyrosinase. When D,L-3-4-dihydroxyphenylalanine (DOPA) is employed as substrate, the inhibition was found to be a competitive-type with Ki of 0.95 μM. We found in addition that thiopronine interacts with the enzymatic generated product (o-quinone) to form a colourless conjugate compound causing an apparent inhibition. These data suggest that thiopronine inhibits mushroom tyrosinase activity in two ways: (1) by forming an adduct with dopaquinone; and (2) by direct interaction with the enzyme probably towards the copper (II) present in the active site or cysteine-rich domains. This finding was indicated by the presence of a lag period prior to the attainment of an inhibited steady-state rate. Both lag period and steady-state rate were dependent on thiopronine and substrate concentrations. An increase of thiopronine concentration causes longer lag periods as well as a concomitant decrease in the tyrosinase activity. The presence of an excess of copper (II) reverses the inhibition exerted by thiopronine.

Original languageEnglish
Pages (from-to)436-442
Number of pages7
JournalBiomedical Chromatography
Issue number7
Publication statusPublished - Sep 2004


  • Adduct formation
  • DOPA
  • Dopaquinone
  • Hyperpigmentation
  • Melanin
  • Tyrosinase

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry
  • Clinical Biochemistry
  • Analytical Chemistry
  • Pharmacology


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