Fig. 2

Addition of glucose helps specify the presence of exoglucanases on 4-methylumbelliferyl β-d-cellobioside (MUC) zymography. a Coomassie Blue staining of native PAGE for D263 crude enzyme. Novozyme 188 (N188) and Geobacillus sp. cellulase A (GsCelA) were negative and positive controls of endoglucanase activity, respectively. b D263 exhibits high endoglucanase activity. CMC zymography was used for detecting endoglucanase activity of the enzyme preparations. c, d D263 shows β-glucosidase activity. 4-Methylumbelliferyl-β-d-glucopyranoside (MUD) zymogram was used for detecting β-glucosidase activity. The addition of 2% glucose successfully represses β-glucosidase activity on the MUD zymography. Commercially available N188, Cellulast 1.5L (C1.5L), Chaetomella raphigera D2 β-glucosidase (D2-BGL) and laboratory-produced Trichoderma cellulase preparation (TRX) were used as positive and negative controls of glucose suppression of BGL activity. e, f D263 shows clear exoglucanase activity. MUC zymogram with 2% glucose addition was used for detecting exoglucanase activity of different cellulase preparations. The modified MUC zymography method can detect exoglucanase activity with little interference from β-glucosidase activity. The protein amount used in a–e was C1.5L, 2600 ng; N188, 150 ng; D263, 340 ng; TRX, 1100 ng; D2-BGL, 100 ng (for MUD assay) and 1000 ng (for MUC assay). All experiments were conducted on 8% native gel with at least three biological replicates