Infective larvae of Strongyloides papillosus, freshly isolated from faeces of experimentally infected rabbits, secreted a collagenolytic metalloproteinase from their oesophageal glands. The enzyme hydrolyzed azocoll at the optimal pH of 8.4 and exhibited a very low activity towards azocasein and azoalbumin at the optimal pH 6.0 and 8.0, respectively. No degradation of elastin-orcein and keratinazure was observed at the pH range of 7.2-10.0. Under histochemical conditions the proteinase hydrolyzed N-acetyl-L- methionine-l-naphthylester at optimal pH 6.8, whereas other synthetic, N-blocked aminoacyl or peptidyl substrates bearing such P₁ amino acids as L-Ala, L-Phe, L-Arg, L-Leu, and L-Lys, were not hydrolyzed. The enzyme was sensitive to refrigeration and underwent inactivation during lyophilization. Unlike most proteinases of other families, the metalloenzyme secreted by S. papillosus larvae was relatively resistant to the inhibitory action of inorganic zinc salts, the decline in the activity in the presence of 1 mM ZnSO₄ was as low as 20%. The organic mercurial pHMB, the nonionic detergent Triton X-100, and calcium ions enhanced the proteinase activity, whereas the cationic detergent cetyltrimethylammonium bromide, the anionic detergent SDS, and the thiol compound dithioerythritol were mild inhibitors. Zinc-chelating compounds 1,10-phenanthroline, N-blocked- L-Pro-L-Leu-Gly hydroxamate, N-blocked L-Pro-L-Leu-L- Ala hydroxamate, and N-carboxymethyl-L-Phe-L-Leu were strong inhibitors, whereas specific inhibitors of serine, cysteine and aspartyl proteinases were without effect on the activity of the larval proteinase. The secretion expelled from the mouth of the larvae avidly absorbed the cationic dye toluidine blue (0.001%) at pH 5.5 and the resulting black complex was water insoluble, thus indicating the presence of a strongly anionic glycoprotein in the secretion, if not an acid glycoprotein nature of the proteinase.
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