Fast solubilization of human lung elastin by Pseudomonas aeruginosa elastase.

Pseudomonas aeruginosa may cause severe lung infections in humans. This bacteria secretes an elastase that might degrade lung elastin. We have studied the solubilization of human lung elastin by P. aeruginosa elastase in an attempt to delineate the pathogenic role of this proteinase in P. aeruginosa lung infections. We also used bovine ligamentum nuchae elastin and human leukocyte elastase for comparative purposes. With an elastin concentration of 5 mg X ml-1 and at physiologic ionic strength, P. aeruginosa elastase is about 50 times more active on human lung elastin than on bovine elastin. In contrast, human leukocyte elastase has similar specific activities on the 2 substrates. In addition, the bacterial enzyme is about 10 times more active on human elastin than the neutrophil elastase but the latter is about 5 times more active on bovine elastin than the former. In order to better quantitate these enzyme-substrate interactions, we have measured initial rates of elastolysis, derived from product versus time curves, as a function of elastin concentration. The substrate-velocity curves, analyzed using an equation similar to the classic Michaelis-Menten one, yielded 2 empirical kinetic parameters: [S50]-1, the apparent elastase-elastin affinity and Vm, the apparent catalytic efficiency of elastase. This analysis shows that human leukocyte elastase exhibits similar [S50]-1 and Vm values for the 2 elastins. The low activity of P. aeruginosa elastase on bovine elastin is due to the combined effects of low S50(-1) and Vm values, which could not be measured separately.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo covalent binding of aminofluorene derivatives to mitochondrial liver DNA of rats pretreated with phenobarbital.

The covalent binding index (CBI) of aminofluorene derivatives (AF) to both nuclear (n) and mitochondrial (mt) hepatic DNA of rats 16 h after i.p. injection of N-acetyl-2-aminofluorene (AAF) has been determined. It was 69 and 212 respectively, i.e. about 3 times higher in mtDNA than in the nDNA. When rats were pretreated for 5 days with phenobarbital (PB) the two CBI decreased in parallel indicating a detoxification of AAF preventing its binding to both nDNA and mtDNA.