Evaluation of silyl-blocked p-nitrophenylmaltoheptaoside as a substrate for alpha-amylase reagents.

We describe a reagent for measuring alpha-amylase (EC 3.2.1.1) activity in serum with use of a thexyldimethylsilyl ether of p-nitrophenyl-alpha-D-maltoheptaoside (SB7) as substrate. This substrate differs from Genzyme's benzylidene-blocked p-nitrophenylmaltoheptaoside substrate (B-PNPG7). The reagent, optimized for the characteristics of the silyl-blocked substrate, contains 4-(2-hydroxyethyl)-1-piperazineethane sulfonate buffer at pH 7.3, alpha-glucosidase (maltase; EC 3.2.1.20), and glucoamylase (EC 3.2.1.3). Comparison with Ciba Corning Diagnostics Corp.'s, amylase reagent with B-PNPG7 as substrate (x) yielded a regression equation of y = 1.20x-2.7 (r = 0.9997). The linear range exceeded amylase concentrations > 2500 U/L and total precision (CV) was 2.3% at an amylase concentration of 112 U/L with the Ciba Corning 550 Express analyzer. Reconstituted reagent is stable for 30 days at 5 degrees C and 7 days at ambient (18-25 degrees C) temperatures.