Inactivation of tyrosinase photoinduced by carboxypterin under solar radiation

IPIÑA, ADRIANA; THOMAS, ANDRÉS H.; DANTOLA, MARIA LAURA

Maresias

Congreso; XII Encuentro Latinoamericano de Fotoquímica y Fotobiología (XII ELAFOT); 2015

UV-A radiation can inducedamage to biomacromolecules through photosensitized reactions. This indirectaction may be mediated by endogenous or exogenous photosensitizers and can takeplace via different mechanisms.   The melanin of the epidermis, is the main protection against theharmful effects of UV solar radiation. Tyrosinase is a glycoprotein that, in mammals, catalyzes therate-limiting step in the synthesisof melanin. Vitiligo is a skin disease that causes lack of pigmentation due toinactivation of enzymes of the melanogenesis. In diseased skin cells micromolarconcentration of pterin derivatives such as carboxypterin (Cap) have beendetermined [1]. A recent study has demonstrated that under UV-A radiation,tyrosinase is inactivated by pterin through a photosensitized process [2]. Moreover,aqueous solutions of pterin derivatives suffer photooxidation under solar  exposure and outdoor conditions [3].   Taking into account that UV light reaches the epidermis, wherepterins derivatives are present in some pathological conditions such asvitiligo, the main aim of this work is to find out if the energy of the sun isenough to cause photoinduced inactivation of tyrosinase using Cap asphotosensitizer. Aqueous solutions containing the enzyme and the photosensitizer were exposedto sunlight and analyzed by UV-Vis spectrophotometry, enzyme activity measurement,fluorescence spectroscopy, electrophoresis (SDS-PAGE) and HPLC.    The results indicated that Cap can photoinactivate the tyrosinaseunder solar radiacion. Upon irradiation tyrosinasestructure and tryptophan residues were altered. [1] K. U. Schallreuter, et. al., Science, 1994, 263, 1444. [2] M. L.Dántola, et. al., Biochem. Biophys. Res. Commun.,2012, 424, 568.[3] A. Ipiña, et. al., Solar Energy, 2014, 109, 45.