Laccase activity tests and laccase inhibitors

Sulfhydryl organic compounds described as laccase inhibitors: dithiothreito l, thioglycolic acid, cysteine, diethyldithiocarbamic acid, and sodium azid e were tested for their activity toward laccase of Trametes versicolor in d ifferent test systems utilising 2,2'-azino-bis-(3-ethylbenzothiazoline-6-su lphonic acid) (ABTS) and 2,6-dimethoxyphenol as enzyme substrates. Only sod ium azide acted as a true laccase inhibitor and showed no significant inter ference with the enzyme tests. All other substances did not significantly i nhibit the laccase activity and the previously reported inhibitory effects result from the reductions of the reaction products such as ABTS radical ca tion and diquinone or subsequent non-enzymatic interactions during substrat e oxidation. The latter apparently forms a complex with unreacted ABTS disp laying varied spectral characteristics and resulting in am underestimation of enzyme activity. (C) 2000 Elsevier Science B.V. All rights reserved.