Comparative study of two ATP: l-arginine phosphotrans-ferases of molecular weight 84 000

Abstract

Solen ensisensis muscle arginine kinase (ATP : l-arginine phosphotransferase, EC 2.7.3.3.) was isolated in an homogeneous state. Its molecular weight was found to be about 80 000. The properties of this enzyme were compared with those of arginine kinase from Sipunculus nudus, an enzyme which also has a molecular weight of about 80 000 Both enzymes have several reactive thiol groups (8 thiol groups in the Solen kinase and 12 in the Sipunculus enzyme were titrateable with 5,5′- dithio-bis-(2- nitrobenzoic ) acid and histidine residues (both enzymes have 6 reactive histidine residues). These kinases were, therefore, highly susceptible to oxidation. Both enzymes show the same pH optimum and absolute specificity towards the guanidine substrate, l-arginine. The reaction kinetics of both enzymes are of the sequential type. In the presence of α-aminoacids or Mg 2+-ADP, similar spectral effects were obtained. The enzymes differ in their enzymic activities and in their rate of recovery following urea denaturation. The most important difference that appeared to be a special feature of the Sipunculus enzyme is that the spectrum of the Mg 2+-ADP-enzyme complex is strongly intensified by l-arginine.