Evidence for Conformational Changes in Tyrosinase During Photoinactivation

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Ultraviolet radiation of 254 nm was found to cause a dose dependent, essentially irreversible inactivation of mushroom tyrosinase (EC1.14. 18.1). Photoinactivation, tryptophan destruction and fluorescence loss obeyed first order kinetics and the apparent first order rate constants being 17.9 x 10^<-2> min^<-1>, 3.7 x 10^<-2> min^<-1> and 6.3 x 10^<-2> min^<-1>, respectively. In contrast to native tyrosinase, photoinactivated enzyme was found to be sensitive towards tryptic attack. The kinetics of tryptic hydrolysis suggested partial unfolding of tyrosinase by UV light. Fluorescence difference spectral studies indicated loss in transfer of excitation energy between tyrosine and tryptophan residues in photoinactivated tyrosinase. The influence of varying radiation dose on tryptic digestibility, intrinsic fluorescence and UV absorption are altogether consistent with the conformational changes associated with photoinactivation of tyrosinase.
日本放射線影響学会の論文