PROPERTIES OF THE EXTRACELLULAR ACIDIC PROTEASES OF DICHELOBACTER-NODOSUS - STABILITY AND SPECIFICITY OF PEPTIDE-BOND CLEAVAGE

Dichelobacter nodosus, a Gram negative obligate anaerobe and causative organism of ovine footrot, secretes a family of extracellular acidic serine proteases with pI's in the range of 5.2 to 5.6, and a basic ser ine protease with a pi of similar to 9.5. The acidic proteases show op timum activity at pH 8 and require a divalent metal ion (eg. Ca2+) to maintain structural integrity. In the presence of EDTA or conditions t hat cause protein unfolding, the proteases undergo rapid and complete autolysis. The proteases were stable to heating to about 50 degrees C for 30 min but at higher temperatures, activity was rapidly lost; viru lent proteases V1 and V2 were slightly more stable (by about 5 degrees C) than benign proteases B2 and B3. The effect of various protease in hibitors on the D. nodosus acidic proteases was the same except that t he inhibitor, chymostatin, markedly inhibited protease V5 but not prot eases V1-3 or B1-B4. Cleavage of the oxidized insulin B-chain showed t hat the specificity of proteases V1-V3 and B1-B4 was identical but tha t it was distinct from that of proteases V5/B5.