Determination of initial enzyme reaction rates from spectrophotometric recordings: A rapid method

Abstract

The initial enzyme reaction rate on a recording spectrophotometer can be expressed as an angle. The tangent of this angle multiplied by a factor derived from the chart speed, chart width, absorbance range, and sample dilution will give the enzyme activity of the sample in mU/ml. The enzyme activity can be tabulated for all angles between 0° and 90° at 0.5° intervals and enzyme activity can be directly read from the table after measuring the value of the angle with a protractor. This technique has been applied to serum cholinesterase assays on the SP 800 recording spectrophotometer and to serum aspartate aminotransferase assays on the LKB 8600 reaction rate analyzer. The method has been shown to be simple, rapid, and more precise than the usual methods of reading these recordings. The sensitivity of the method is known (unlike the usual methods) and the relative error can be calculated. The accuracy of the method is similar to the other manual methods. This technique is quite general and it can be applied to all initial enzyme reaction rate determinations.