Studies on alkaline phosphatases. 4. Influence of dietary minerals on pH optima and reaction velocities of phosphatases of fowl

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Abstract
In the presence of 10 mM-Mg2+ ions the optimum pH of alkaline phosphatase of intestinal mucosa was lower in fowls fed on a low-calcium diet than in those fed on a high-calcium diet. When no Mg2+ ions were added to the reaction mixtures, the optimum pH was higher in fowls given a low-calcium diet than in those given a high-calcium diet. Supplemental dietary magnesium reduced the difference in pH optima of intestinal phosphatases of pullets fed on low- and high-calcium diets when the activities were measured with and without added Mg2+ions in the reaction mixtures. High dietary magnesium, however, did not eliminate the change in pH optima to lower values when Mg2+ ions were added to the reaction mixture. The phosphatase activity of intestinal mucosa, which was high in chicks at 1 day of age, declined at a much faster rate in birds given a high-calcium diet than in birds given a low-calcium diet. High dietary magnesium also caused a rapid decrease in the enzyme activity. High dietary calcium caused intestinal phosphatase activity to decline to a low level before an appreciable difference developed in the optimum pH for the enzymes of chicks given a low-calcium diet and those given a high-calcium diet; the difference in optimum pH, due to the amount of calcium in the diets, persisted after the enzyme activity of birds fed on a low-calcium diet had also declined to a low level. The interchanging of the low- and high-calcium diets at intervals of 2 and 5-6 days resulted in reversals of the quantitative activities of intestinal phosphatase and the amounts of mucosa obtained from the duodenum of chicks. The quantitative activity of intestinal phosphatase of chicks fed on a low-calcium diet was not influenced by the addition of inactivated (heated at 80[degree] for 30 min.) enzyme preparation of chicks fed on a high-calcium diet, and the activity of the enzyme preparation of chicks fed on a high-calcium diet was not altered by inactivated mucosa of chicks fed on a low-calcium diet. The reaction velocity of a mixture of the active preparations from the two dietary groups of chicks was approximately equal to the sum of the activities of the two preparations measured separately. In the presence of 10 mM-Mg2+ ions the optimum pH of intestinal phosphatase was lower in birds given diets supplemented with manganese or molybdenum than in birds given the unsupplemented diets. Dietary supplements of manganese or molybdenum caused an increase in the phosphatase activity of intestinal mucosa.