Activities of histone debiotinylases in nuclear extracts from human cells depended on the tissue from which cells originated. Nuclear extracts were prepared from HCT 116 colorectal carcinoma, NCI-H69 small lung cancer, JAr choriocarcinoma, HepG2 hepatocarcinoma and Jurkat lymphoma cells and debiotinylase activities were quantified by plate assay at pH 7.4. a,b,cColumns not sharing the same letter are significantly different (P< 0.05; n = 3).