The Electron‐Accepting Sites in Rhus vernicifera Lacase as Studied by Anaerobic Oxidation‐Reduction Titrations

Abstract

Laccase fdrom Rhus vernicifera was titrated under anaerobic conditions using quinol as the reducing substrate, and changes in the optical and electron paramagnetic resonance specta were measured. Titrations of native laccase as well as enzyme in the presence of the inhibitor, fluoride, demonstrated tht four electrons were required to reduce completely the enzyme as determined by the measurements noted above. The titrations of native laccase three different types of electorn‐accepting sites in the molecule. Type 1 copper is associated with the strong absorption band at 614 nm and has a potential of 420 mV. Type 2 copper has the lowest potential, 390 mV, and could not be correlated with any of the resolvable absorption bands in the visible spectrum. The absorption band at 330 nm is suggested to arise from a two‐electron accepting chromophore wiith an oxidation‐reduction standard potential of 460 mV at pH 7.5. In the presence of excess fluoride, the oxidation‐reduction potential of some sites was changed with the result that all sites appear to get the same potential. The nature of the two‐electron accepting chromophore is discussed in terms of its properties, and these are consistent with the concept that it contains the tw copper ions undectable by electron paramagnetic resonance as a cupric‐cupric pair in the oxidized enzyme. Copyright © 1971, Wiley Blackwell. All rights reserved