tailieunhanh - Báo cáo khoa học: Mutational analysis of substrate recognition by human arginase type I ) agmatinase activity of the N130D variant

Upon mutation of Asn130 to aspartate, the catalytic activity of human arginase I was reduced to 17% of wild-type activity, theKmvalue for arginine was increased 9-fold, and thekcat ⁄Kmvalue was reduced 50-fold. The kinetic properties were much less affected by replacement of Asn130 with glutamine. | ỊFEBS Journal Mutational analysis of substrate recognition by human arginase type I - agmatinase activity of the N130D variant Ricardo Alarcon Maria S. Orellana Benita Neira Elena Uribe Jose R. García and Nelson Carvajal Departamento de Bioquimica y Biologia Molecular Facultad de Ciencias Biologicas Universidad de Concepcion Chile Keywords agmatine arginase asparagine 130 human liver substrate specificity Correspondence N. Carvajal Departamento de Bioquimica y Biologia Molecular Facultad de Ciencias Biologicas Universidad de Concepcion Casilla 160-C Concepcion Chile Fax 56 41 239687 Tel 56 41 2204428 E-mail ncarvaja@ Received 29 August 2006 revised 13 October 2006 accepted 23 October 2006 doi Upon mutation of Asn130 to aspartate the catalytic activity of human arginase I was reduced to 17 of wild-type activity the Km value for arginine was increased 9-fold and the kcat Km value was reduced 50fold. 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 kcav Km values of X 103 M-1-s-1 and X 103 M-1-s-1 respectively . After dialysis against EDTA and assay in the absence of added Mn2 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. Arginase L-arginine amidino hydrolase EC catalyzes the hydrolysis of L-arginine to the products L-ornithine and urea. The enzyme is widely distributed .