Reaction rate assay of serum sorbitol dehydrogenase activity at 37°C

Abstract

The sorbitol dehydrogenase (EC 1.1.1.14) activity of human serum and liver was investigated at 37°C. Various buffers were examined but tris(hydroxymethyl)aminomethane HCl in a final concentration of 90 mmol/liter (pH 6.6, at 37°C) was the one with which activity was the greatest. The enzyme is inhibited by its substrate, D fructose, and activity was greatest with a substrate concentration (in the final assay mixture) of 500 mmol/liter and an NADH concentration of 247 μmol/liter. The specimen volume was 100 μl. The enzyme from liver and serum was shown to have similar K(m) values and activation energies, and the authors conclude that the liver enzyme was unchanged on passing into the extrahepatic space. Normal values for this assay are 0-2.6 U/liter (2.5 and 97.5%).