On the influence of the substrate (elastin) in elastase-alpha 1 antitrypsin interactions

Evidence is presented showing that elastin(s) influences the interactions between porcine pancreatic elastase and its main plasma inhibitor alpha 1-proteinase inhibitor (e.g. alpha 1 antitrypsin). The rate constant of association (kon) between the proteinase and alpha 1 antitrypsin is decreased from 2.8 10(5) M-1 sec-1 to 1.24 10(5) M-1 sec-1 in presence of 1 mg/ml of insoluble elastin and 0.83 10(5) M sec-1 in presence of the same concentration of alpha-elastin. With both elastins this kon decrease was found concentration dependent indicating that these compounds compete in a similar fashion with alpha 1 AT for the binding of elastase. Such an effect was not observed when elastin(s) was replaced by bovine serum albumin. Experiments were designed as previously published (B. Robert et al. 1974) in order to evaluate the capacity of alpha 1 AT to inhibit preadsorbed elastase on to insoluble elastin and also diffusible protease molecules. It was found that even at concentrations far exceeding the equivalence with elastase, alpha 1 AT was only partially able to inhibit both preadsorbed enzyme (approximately 50 per cent) and diffusible protease (approximately 90 per cent).