Maltotetraose as a substrate for enzyme-coupled assay of amylase activity in serum and urine.

The use of maltotetraose ss a new substrate for the enzyme-coupled determination of amylase activity in biological fluids was developed by Beckman Microbics. We evaluated a manual and a centrifugal analyzer version of the method in comparison with two commonly used manual starch-dye amylase techniques: Roche Amylochrome and Pharmacia Phadebas. Both maltotetraose amylase procedures proved to be rapid and precise, and results correlated satisfactorily with the starch-dye methods for serum and urine samples.

Comparison of radioimmunoassay with homogeneous enzyme immunoassay for the determination of theophylline concentration in serum.

The homogeneous enzyme immunoassay (EMIT) and radioimmunoassay (RIA) procedures for the quantitation of theophylline concentrations in serum were evaluated and compared. Both methods exhibited curves linear over the therapeutic range (range of concentration, 2.0-33.0 microgram/ml). Precision was acceptable for both methods with the coefficient of variation being less than 8.3%. The RIA procedure was found to be slightly more precise. The correlations between the EMIT and RIA procedures was found to be sufficient to allow the procedures to be used interchangeably. This would facilitate the test availability on a 24 hr, 7 day basis.

Enzymatic method for determination of CO2 in serum.

We describe an enzymatic method, requiring only 10 mul of serum, for determining CO2 as bicarbonate or dissolved gas. Phosphoenolpyruvate carboxylase catalyzes the reaction of HCO3- with phosphoenolypyruvate to give oxalacetate. The resulting NADH, in the presence of malate dehydrogenase, is oxidized to NAD+, and the decrease in absorbance at 340 nm is directly proportional to the amount of CO2 present in the sample. Reaction is complete in 3 to 6 min under assay conditions, and is linearly related to CO2 concentrations between 8 and 65 mmol/liter. Analytical recovery is 95-110% (average, 101%). Two laboratories compared values obtained by continuous-flow analysis. The resulting correlation coefficients were 0.966 and 0.987, values for the t-test were t(paired) equals 0.473 and t(paired) equals 0.334, and average day-to-day precisions (three concentrations) were 3.9% and 4.2%.