Continuous kinetic assay of arylsulfatases with new chromogenic and fluorogenic substrates

A fluorogenic substrate for the continuous assaying of aryl sulfatases

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.

New fluorogenic substrate for the first continuous steroid sulfatase assay

The screening for new inhibitors of steroid sulfatase requires an efficient test system. To overcome the shortcomings of the available discontinuous fluorimetric assay, several coumarin-type compounds were investigated as potential new substrates. 3,4-Benzocoumarin 7-O-sulfate was found to have appropriate substrate properties for the establishment of the first direct continuous assay of steroid sulfatase.

Fluorometric continuous kinetic assay of alpha-chymotrypsin using new protease substrates possessing long-wave excitation and emission maxima

A direct and continuous kinetic method for the fluorometric determination of alpha-chymotrypsin and trypsin is described, and 2-aminoacridone (2-AA) is introduced as a promising new fluorophore in analytical biochemistry. N-Succinyl- and N-glutaryl-phenylalanine as well as N-benzoylarginine were coupled to 2-AA via a peptide bond and the resulting fluorogenic substrates are shown to be cleaved by the two enzymes. Since the substrate and product of hydrolysis have quite different spectral properties, the increase in the long-wave fluorescence of 2-AA (measured at 570 nm under 450-nm excitation) is a parameter for the enzyme activity. Chymotrypsin (0.5 microgram/ml) and trypsin (0.1 microgram/ml) were detectable in a 3-min assay. The major advantages of the new substrates over existing ones are the analytical wavelengths which are distinctly outside the background fluorescence of most biological matter and the somewhat faster reaction rates which can reduce the time of analysis.

A sensitive kinetic assay of serum albumin based on its enzyme-like hydrolytic activity, using a new chromogenic and fluorogenic substrate

A new albumin assay, based on the unusual enzyme-like activity of the protein that promotes hydrolysis of ester bonds in fatty acid arylesters was designed for clinical routine use. The substrate introduced shows improved analytical wavelengths and is suitable for both photometric and fluorimetric assay. Experiments have been performed with a conventional photometer, a fluorimeter and a Cobas Fara autoanalyzer. Detection limits are as low as 10 micrograms/ml photometrically and 20 ng/ml fluorimetrically. The method provides a sensitive quantitative determination of even minute amounts of albumin in liquid solution, and a simple semiquantitative test may be performed by fixing the dye on a test strip which then is immersed into a sample solution and observing the development of yellow color intensity.

The effect of fatty acid chain length on the rate of arylester hydrolysis by various albumins

A series of synthetic chromogenic and fluorogenic substrates for monitoring the arylesterase-like activity of albumins from various sources has been studied. Except for ovalbumin, all displayed enzyme-like activity. The acetate, butyrate, caprylate, laurate, and palmitate esters of a coumarin dye were found to be efficiently hydrolyzed within the pH range 8.8-9.8, with the non-enzymatic rate being highest for acetate and lowest for laurate. The latter is considered to be the substrate of choice because it is cleaved most quickly by the proteins tested. A considerable increase in hydrolytic activity was observed upon addition of detergents, but not of Ca and Mg ions, while addition of 1 equivalent of lauric acid to BSA resulted in a 30% decrease in its activity. The results are interpreted in terms of the well-known affinity of albumins for long chain fatty acids and provide the basis for a sensitive determination of small amounts of albumins.