Characteristics of the inhibition of serum alkaline phosphatase by theophylline.
1. The effect of various parameters on the inhibition of alkaline phosphatase activity by theophylline was studied. The influence of pH is great, being optimum for a value of 9.4. The temperature and the magnesium ion concentration have no to low effect. 2. The nature of the substrate and the nature of the buffer in which the enzymatic activity is measured have an effect:by measuring the activity of alkaline phosphatase in serum by a method with phenolphthaleinphosphate in Tris buffer, a negligible interference by therapeutic or toxic levels of theophylline is observed. 3. The inhibition by theophylline varies greatly with the origin of alkaline phosphatase: the liver isoenzyme is strongly inhibited, the intestinal one to a lesser degree and the placental isoenzyme almost not inhibited. 4. The inhibition of the liver and intestinal isoenzymes are uncompetitive and the inhibition constants were measured.
Characteristics of the inhibition of serum alkaline phosphatase by theophylline. 1. The effect of various parameters on the inhibition of alkaline phosphatase activity by theophylline was studied. The influence of pH is great, being optimum for a value of 9.4. The temperature and the magnesium ion concentration have no to low effect. 2. The nature of the substrate and the nature of the buffer in which the enzymatic activity is measured have an effect:by measuring the activity of alkaline phosphatase in serum by a method with phenolphthaleinphosphate in Tris buffer, a negligible interference by therapeutic or toxic levels of theophylline is observed. 3. The inhibition by theophylline varies greatly with the origin of alkaline phosphatase: the liver isoenzyme is strongly inhibited, the intestinal one to a lesser degree and the placental isoenzyme almost not inhibited. 4. The inhibition of the liver and intestinal isoenzymes are uncompetitive and the inhibition constants were measured.