Oxidation and Reduction of Copper Ions in Catalytic Reactions of RHUS Laccase

Abstract

The latex of lacquer tree, urushi, contains 50–80% urushiol which is a derivative of catechol (1–3). Urushiol in the latex undergoes rapid oxidation when exposed to air and the resultant quinone polymerizes to form a dark and lusterous solid film in combination with polysaccharides and other substances in the latex. The urushi film is superior in mechanical strength and stability against most of the chemicals and aging: thus it has been used in oriental countries in manufacturing lacquer wares in the past thousands of years. The aerobic oxidation of urushiol in the latex is catalyzed by laccase. In 1883 Yoshida (4) obtained an alcohol-soluble material and an alcohol-insoluble but cold water-soluble material from the latex. The former (urushiol) did not by itself undergo characteristic drying, as the original latex, on contact with air. The latter contained a heat-unstable, nitrogenous substance having “diastatic” properties. Yoshida found that when the former was acted by the latter substance, a dry film of urushi was formed at 20°C and the drying process required moisture and atmospheric oxygen. This is the first establishment of the characteristics of the catalyst in the latex at the time when biochemistry was only in its very early stage of development.