Influence of bivalent cations, phosphate and complexing substances on inorganic pyrophosphate in the microsomal fraction of isolated rat odontoblasts.

The influence of three diphosphonates, ethane-1-hydroxy 1.1. diphosphonate, methane-diphosphonate and dichloromethane diphosphonate, on inorganic pyrophosphatase (PPiase, E.C. 3.6.1.1.) was investigated. The inhibition by the diphosphonates appeared to be due to their complexation with a bivalent cation, probably Zn2+, which acts as a cofactor for the enzyme. The influence of calcium and inorganic phosphate (Pi) on the PPiase activity was studied in the presence and absence of several complexing substances, including the diphosphonates. Ca2+ alone inhibited the enzyme whereas, in the presence of EDTA, a Ca2+ stimulation of the PPiase was observed which was substrate-dependent and had an optimal activity at a Ca2+:PP4-i ratio of 1:1. There was a small inhibition of the PPiase activity by Pi which was not influenced by the substrate used.