Cytochemical location of urease in the cell wall of two different lichen phycobionts

The enzyme urease has been located in the cell wall of recently isolated phycobionts from Evernia prunastri and Xanthoria parietina lichens. Cytochemical detection is achieved by producing a black, electron-dense precipitate of cobalt sulfide proceeding from CO 2 evolved from urea in the presence of cobalt chloride. Cellular fractionation reveals that about 80% of total urease activity was associated to the cell wall on both phycobionts whereas only 20% was recovered as soluble protein.