Human serum β-glucuronidase; its measurement and some of its properties

Abstract

Human serum β-glucuronidase has a high requirement of phenolphthalein β- d-glucosiduronic acid for its saturation as evidenced by the apparent K m value of 0.002 M. The digest containing 0.006 M substrate ensures an elevated linear rate as a function of serum concentration which permits the reduction of incubation time to 4 h. One can expect a variation of between 1.4 and 6.5% in replicate determinations depending on the enzyme level. The role of circulating saccharolactone, an endogenous β-glucuronidase inhibitor, was found to be minimal following the study of the effect of dialysis on enzyme activity. Serum values in normal individuals and in patients with diabetes, liver cirrhosis and cancer are reassessed and were found to be approximately twice the previously reported values. Conditions have also been recommended for the use of alternate substrates, i.e. β- d-glucosiduronic acids of p-nitrophenol and 8-hydroxyquinoline. Finally, factors of biochemical specificity, of integrity of subcellular organelles and genetics are dealt with in the evaluation of the significance of serum β-glucuronidase values.