The structure and function of the N-linked carbohydrate chains in laccase 111, one of the ligninolytic glycoenzymes from the white-rot fungus Cuviulus versiculuv, have been partially characterized using endoglycosidases (Endo F and Endo H) and the N-asparagine-specific inhibitor, tunicamycin. In the presence of 10 pg tunicamycin ml-' laccase and proteinase activities in culture filtrates of C. vevsiculur were measured over 3 weeks. Laccase activity was slightly decreased by the addition of tunicamycin, whereas proteinase activity was increased. The N-linked carbohydrate chains were not necessary for laccase secretion and activity. Endo-glycosidase digestion showed that laccase I11 contained at least four N-linked carbohydrate chains, of which two were high-mannose type or hybrid type and two were complex type. Judging from the differences in the resistance of the native and the carbohydratedepleted laccase to proteolytic digestion and high temperature, the four N-linked carbohydrate chains have important protective functions against proteolytic attack and elevated temperature.

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