A fluorogenic substrate for phosphatases. It is widely used for detecting phosphatases in solution. However this phosphatase substrate is not well suited for living cell or continuous assays since MU (4-methylumbelliferone), the enzymatic product, which only develops maximum fluorescence at pH value of >10. Thus it is also difficult to use MUP for the detection of phosphatases that have acidic optimal pH range such as acid phosphatases. ABD Bioquest is pleased to offer MUP Plus that is developed to address this pH limitation associated with MUP substrates.