The mouse Nudt7 gene encodes a peroxisomal nudix hydrolase specific for coenzyme A and its derivatives

A mouse homologue of the Saccharomyces cerevisiae Pcd1p coenzyme A diphosphatase, NUDT7alpha, has been expressed as a thioredoxin fusion protein in Escherichia coli. NUDT7alpha is also a CoA diphosphatase of the nudix hydrolase family, and hydrolyses CoA, CoA esters and oxidized CoA with similar efficiences, yielding 3',5'-ADP and the corresponding 4'-phosphopantetheine derivative as products. K(m) and k(cat) values with CoA were 240 microM and 3.8 s(-1). Activity was optimal at pH 8.0 with 5 mM Mg(2+) or Mn(2+) ions, while fluoride was inhibitory with an IC(50) value of 20 microM. Expression of the Nudt7 gene was highest in liver, intermediate in lung and kidney, and lowest in brain and heart, producing a 1.5 kb transcript. A similar pattern of expression was found for the human orthologue, NUDT7. An enzymically inactive splice variant, NUDT7beta, which lacks 20 amino acids downstream of the nudix motif, was also found to be expressed in mouse tissues. Transfection of HeLa cells with a vector expressing the Nudt7alpha gene fused to the C-terminus of red fluorescent protein showed that NUDT7alpha, like Pcd1p, was a peroxisomal enzyme. The function of the NUDT7 enzyme may be the elimination of oxidized CoA from peroxisomes, or the regulation of CoA and acyl-CoA levels in this organelle in response to metabolic demand.