The specificity of the major (70 kDa) protease secreted by Aeromonas salmonicida

Abstract

Abstract. The specificity of the major protease secreted by Aeromonas salmonicida has been explored using a number of proteins and p‐nitroanilides as substrates. The 70kDa protease was found to hydrolyse two p‐nitroanilides which have been reported to be specific substrates for thrombin. Kinetic parameters (kcat, and Km) were compared for the 70kDa protease and for thrombin as were the effects of a number of inhibitors. The 70kDa protease is able to degrade proteins which have a relatively open structure, for example, caseins or denatured bovine scrum albumin, to small fragments mostly of Mr<2500. However, proteins with a more compact structure are more resistant to the protease. It was concluded that the 70kDa protease shows some of the specificity features of thrombin, although it is less discriminating in its choice of both low and high Mr substrates than thrombin. In preliminary experiments, the 70 kDa protease was found, like thrombin, to decrease the clotting time of rainbow trout blood. The possible physiological significance of these results is discussed.