Inorganic Pyrophosphatase of Clofibrate-Induced Rat Liver Peroxisomes

Clofibrate increased inorganic pyrophosphatase (PPase) activity in peroxisomes more than 12-fold (740 milliunits/head, 15.9± 5.0 milliunits/mg protein) in rat liver. The distribution of cytochrome c oxidase and that of the PPase in a Nycodenz gradient suggested that the PPase is an original peroxisomal enzyme and not a mitochondrial contaminant: This was confirmed by second Nycodenz gradient centrifugation. The optimum pH of the peroxisomal PPase was about 8.5. The activity was specific to inorganic pyrophosphate (PPi), the K value for PP, being 34.1 ±3.3 fiM. It was strictly dependent on Mg2+ and showed a sigmoidal dose-response for Mg2+ with an So.s value of 100 μM. The activity was inhibited by Ca2+, p-chloromercuriphenylsulfonic acid, Hg2+, iV-ethylmaleimide, and NaF. The functions of peroxisomal PPase are discussed.