Syntheses of 4-methylumbelliferyl-beta-D-xylobioside and 5-bromo-3-indolyl-beta-D-xylobioside for sensitive detection of xylanase activity on agar plates.

4-Methylumbelliferyl-beta-D-xylobioside (MU-X2) and 5-bromo-3-indolyl-beta-D-xylobioside (BI-X2) were synthesized as substrates for the detection of xylanase activity on agar plates. A family F/10 xylanase from Streptomyces olivaceoviridis E-86 (FXYN) was able to be more sensitively detected than RBB-xylan by using MU-X2 as a substrate. A mutant xylanase E128H/FXYN having only 1/1000 of the activity of FXYN was also able to be detected on the MU-X2 plate but was not detected on the RBB-xylan plate. A family G/11 xylanase from Streptomyces lividans 66 (Xyn B) was not detected on the MU-X2 plate, but it was able to be detected on the RBB-xylan plate, suggesting that the MU-X2 substrate is specific to family F/10 xylanases. However, none of the xylanases were detected effectively by using BI-X2 as a substrate.