Fluorometric measurement of urinary alpha-L-iduronidase activity

A fluorogenic substrate for alpha-L-iduronidase, 4-methylumbelliferyl alpha-L-iduronide, has been newly synthesized and the enzyme activity has been measured in urine samples obtained from normal persons and patients suffering from mucopolysaccharidosis. Urine samples derived from a patient with Scheie syndrome showed greatly reduced activity compared with a normal adult at a similar age. This patient exhibited a high level of urinary excretion of dermatan sulfate and heparan sulfate, which could be interpreted in terms of her low alpha-L-iduronidase activity. The use of the fluorogenic substrate has some advantages over existing methods because of the high sensitivity and the relative ease of handling, and it should be useful not only for diagnosis but also for following the purification process of the enzyme.