Abstract
1. The exchange reaction of laccase copper with ionic copper under varying conditions was studied using radioactive copper as the tracer.
2. The copper atom of oxidized laccase did not exchange with cupric ion in the medium. The copper-protein linkage of oxidized laccase must be very stable.
3. The copper atom of reduced laccase exchanged with cuprous ion rapidly, but it can not be replaced by the cupric ion in the medium.
4. The copper atom of laccase exchanged with ionic copper while the enzyme was catalyzing the oxidation of hydroquinone, and the extent of exchange increased with the amounts of hydroquinone oxidized, but the velocity of exchange was very slow compared with the rapid exchange reaction between reduced laccase and cuprous ion.
The author wishes to express his hearty gratitude to the late Prof. A. Nishimura for his interest and encouragement during this investigation, and to Prof. Y. Ogura, University of Tokyo, for his valua-ble advices. Thanks are also due to Mr. K. Kita-mura for his co-operation in this work, and to Saito Co. Ltd. for the kind supply of lacquer latex.
