Copper Ions are Potent Inhibitors of Intestinal Phosphatases in the Pig

Abstract

Abstract The phosphohydrolase activity of small intestinal mucosa was investigated in vitro in the pig. The activity was studied using four different enzyme substrates at physiological pH levels actual in the duodenum-jejunum part of the gastrointestinal tract, i.e. 5.0, 5.8, 6.6 and 7.4. The enzymatic action was tested towards four inhibitors, known to be suppressive to specific phosphatases located in other regions of the organism, in order to compare the kinetics of intestinal phosphatases versus other phosphatases. Phosphohydrolase activity in the mucosa was evident at the physiological pH levels. The scale of activity was highly dependent upon pH and enzyme substrate used. L(+)tartrate appeared to be a potent inhibitor in concentrations between 10 and 80 mmol 1−1 although the response was not consistently dose dependent. Sodium fluoride, in a 50 mmol 1−1 concentration, on average depressed phosphatase activity by 40%, while molybdate in concentrations up to 100 μmol 1−1 had only a marginal effect on the activity (mean inhibition 13%)—strictly in contrast to acidic phosphatases of bone osteoclasts. Copper ions exerted a significant depression on phosphatase activity towards three out of four substrates, even at concentrations of 2–20 μmol 1−1. This effect may be of nutritional importance, because young pigs are traditionally fed high levels of copper sulphate to stimulate growth. The consequences of this feeding practice on the phosphatases in the mucosa and the nutrient absorption are not known, and the effect upon other intestinal enzymes also remains unknown.