Ahmed V, Ispahany M, Ruttgaizer S, Guillemette G, Taylor SD. A fluorogenic substrate for the continuous assaying of aryl sulfatases.
Anal Biochem 2005;
340:80-8. [PMID:
15802133 DOI:
10.1016/j.ab.2005.02.007]
[Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Indexed: 10/25/2022]
Abstract
The most common fluorogenic substrate for assaying aryl sulfatases (ARSs) is 4-methylumbelliferyl sulfate (MUS). However, ARSs operate optimally at pH values that are less than the pK(a) (7.8) of the reaction product of MUS, 4-methylumbelliferone (4-MU). Thus, a major disadvantage of this assay is that it is usually run in a discontinuous mode due to the need for basification of the reaction mixture to achieve complete ionization of the phenolic products and maximum fluorescence. To circumvent this problem, 6,8-difluoro-4-methylumbelliferyl sulfate (DiFMUS) was prepared and examined as a substrate for ARSs. The product of the reaction is 6,8-difluoro-4-methylumbelliferone, a known coumarin with fluorescent properties equal to those of 4-MU, and has a pK(a) of 4.9. This allowed for the continuous assaying of human placental ARSs A, B, and C, which operate optimally between pH 5.0 and pH 7.0. Furthermore, DiFMUS exhibited a lower K(m) (up to 20-fold) for the ARSs than did MUS; for ARSA and ARSB, it exhibited a greater V(max) than did MUS. This substrate should have considerable utility for the continuous assay of ARS activity.
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