A note on the use of dinitrosalicylic acid for determining the products of enzymatic reactions

Factors contributing to non-linearity of enzyme assays incorporating detection of reaction products using dinitrosalicylic acid (DNS) are discussed. The common practice of diluting reaction products before quantification of reducing compounds is shown to be one cause of non-linearity. Insufficiency of substrate is also an important contributory factor in most modern versions of the method, although the original procedure was correctly designed to ensure a linear reaction. The inherent inaccuracy involved in expression of the results of non-linear reactions in units implying linearity (katals or International Units) is emphasized.