alpha-Amylase activity by the Beckman reaction system and suppression by pyruvate

We evaluated the new Beckman Enzymatic Amyalse-DS Method with maltotetraose as substrate. Our findings indicate that the method is approximately twice as sensitive as the old method involving soluble starch [Clin. Chem. 24, 762 (1978)]. The new method also shows a linear rate of reaction, in contrast to the curvilinear rate previously observed with the old method. The Km with maltotetraose is 0.77 g/L, or about twice that with soluble starch (0.42 g/L). The method correlates well with the Phadebas alpha-amylase method (r = 0.974 and 0.991 on 84 serum and 52 urine specimens, respectively). Of 43 specimens with high concentrations of pyruvate we examined for interference with alpha-amylase activity, only six showed interference when maltotetraose was the substrate. (With both Beckman methods the reaction of pyruvate with NADH produced lactate and NAD+ in the presence of lactate dehydrogenase as contaminant.) Pyruvate interference decreased with increases in (a) the alpha-amylase activity of the specimen, (b) the amount of NADH initially present in the maltotetraose reagent, and (c) the length of time the reconstituted maltotetroase reagent was allowed to stand before being used.