SEASONAL-VARIATION OF TYROSINASE ACTIVITY IN SERUM

Serum samples for the analysis of tyrosinase activity were obtained fr om 10 healthy subjects in autumn, winter and summer. Tyrosinase was pu rified from 100 mu l serum by adsorption to concanavalin A sepharose, the tyrosinase adsorbed to the gel being separated from other componen ts by centrifugation. The gel was suspended in a buffer containing 5-h ydroxy-indole-3-acetic acid as an antioxidant and incubated for 2 min with L-cysteine and D-L-dopa at 37 degrees C. The 5-S-L-cysteinyl-L-do pa formed was measured by HPLC and electrochemical detection. Tyrosina se has high stereo-specificity for the L-enantiomer of dopa, and corre ction for non-specific oxidation was made by simultaneous measurement of 5-S-L-cysteinyl-D-dopa formed from D-dopa. Whereas the oxidation of L dopa catalysed by tyrosinase was inhibited by L-tyrosine, the nan-s pecific oxidation of D-dopa was not. Mean serum tyrosinase activity wa s 0.9 nkatal/l in summer, 0.8 nkatal/l in autumn and 0.4 nkatal/l in w inter. The range of tyrosinase activity was much higher in summer and autumn than in winter.