Chick Aorta Pyrophosphatase 1

Abstract

Summary

Chick aorta inorganic pyrophosphatase is inhibited by collagen and micromolar amounts of calcium. These effects may be important in the regulation of aorta calcification by controlling the degree to which PP_i in aorta tissue is hydrolyzed. The pH optima for the enzyme is near pH 8.0. The apparent binding constant for the substrate is 7 × 10^-4 M, once it is associated with magnesium (Mg₂P₂O₇ ^2–). Magnesium was the only cation that markedly stimulated activity. At pH 8.0, inorganic pyrophosphate appears to be the primary substrate for the enzyme. The effect of magnesium-deficiency on pyrophosphate levels appeared most related to the elevation of calcium in tissue extracts which concomitantly resulted in partial inhibition of the extracted enzyme activity.