Abstract

Upon mutation of Asn130 to aspartate, the catalytic activity of human arginase I was reduced to ∼17% of wild-type activity, the K m value for arginine was increased ∼9-fold, and the k cat/K m value was reduced ∼50-fold. The kinetic properties were much less affected by replacement of Asn130 with glutamine. In contrast with the wild-type and N130Q enzymes, the N130D variant was active not only on arginine but also on its decarboxylated derivative, agmatine. Moreover, it exhibited no preferential substrate specificity for arginine over agmatine (k cat/K m values of 2.48 × 10 3 m -1·s -1 and 2.14 × 10 3 m -1·s -1, respectively). After dialysis against EDTA and assay in the absence of added Mn 2+, the N130D mutant enzyme was inactive, whereas about 50% full activity was expressed by the wild-type and N130Q variants. Mutations were not accompanied by changes in the tryptophan fluorescence properties, thermal stability or chromatographic behavior of the enzyme. An active site conformational change is proposed as an explanation for the altered substrate specificity and low catalytic efficiency of the N130D variant. © 2006 The Authors.