4methylumbelliferyl

4-methylumbelliferyl (often abbreviated 4-MU) denotes a coumarin-derived fluorogenic group used widely in biochemical assays. In practice the term commonly refers to substrates in which an enzymatic cleavage releases 4-methylumbelliferone (7-hydroxy-4-methylcoumarin), a small molecule that exhibits strong blue fluorescence. Because the conjugated substrate is only weakly fluorescent, enzymatic hydrolysis produces a large increase in signal that is readily measured.

4-MU-based substrates are available for many hydrolases and transferases, including glycosidases (for example 4-methylumbelliferyl-β-D-glucuronide, MUG), phosphatases and sulfatases. They are used in enzyme kinetics, clinical and environmental microbiology (e.g., detection of β-glucuronidase activity in water testing), and high-throughput screening because they allow continuous, sensitive assays in microplates.

Photophysical properties include excitation in the near-UV (around 360–365 nm) and emission in the blue region (approximately 440–460 nm). Fluorescence intensity is pH-dependent because the phenolic form of 4-methylumbelliferone is more fluorescent; signals are typically stronger under alkaline conditions. Advantages of 4-MU substrates include high sensitivity and compatibility with real-time measurements; limitations include requirement for UV excitation, pH sensitivity, potential sample autofluorescence and photobleaching.

Handling follows standard laboratory chemical safety practices; specific hazard information depends on the exact derivative in use.