Activation parameters for the reconstitution of apotyrosinase by copper

Abstract

The reaction of apotyrosinase with divalent copper to give enzymatically active tyrosinase has been studied at pH 8.2 and temperatures from 278 to 303 K. At a 10-fold excess of Cu(II) over enzyme, the pseudo-first order rate constants range from 1.32 × 10−3 s−1 to 2.93 × 10−2 s−1 and yield activation parameters of ΔH≠ = 85 ± 3 kJ∙mol−1 and ΔS≠ = 5 ± 20 J∙mol−1∙K−1. The near zero value for the entropy of activation is discussed.Key words: tyrosinase, copper.