Dr. Murai Éva szerk.: Parasitologia Hungarica 12. (Budapest, 1979)
Measurements on a natural substrate (haemoglobin) at an acid pH, under activation with cysteine, have substantiated the earlier implication that the liver fluke also possesses proteases functioning in acid conditions (pH 1.5, 2.8, 3.5, 5.0). This accords well with the pertinent findings of PENNOIT de COOMAN and van GREMBERGEN (1942), HALTON (1967) and LOCATELLI and BERETTA (1969). The experimental observation that addition ofcysteine-HCl accounted for an about twofold activity increase of the proteases at pHs 2.8, 3. 5 and 5.0 supported their cathepsin-like nature. Our experiments on flukes with sealed oral sucker have substantiated the observation of others (THORSELL and BJÖRKMAN, 1965; LOCATELLI and BERETTA, 19 69) that the flukes release the digestive enzymes through their oral opening. Extra-corporeal digestion seems to play a substantial role in the nutrition of the liver fluke. The released proteases account for lysis of the surrounding host tissue and for partial digestion of the blood before its complete breakdown in the digestive tract. The production of protease inhibitors by parasites has long been known (von BRAND, 1973). It has been extensively studied in Nematodes, and recently it has been demonstrated also in Cestodes (MATSKÁSI and JUHÁSZ, 1977). The present experiments have substantiated the presence of protease inhibitors in the liver fluke. Their biological role was much disputed, (von BRAND, 1973) recently the original explanation that they protect the parasite from the digestive enzymes of the host has gained ground again (PAPPAS and READ, 1972, b; JUHÁSZ, 19 79). Flukes incubated in maintenance medium inactivated added bovine trypsin and chymotrypsin. The incubation medium did in itself depress the activity of host proteases after removal of the flukes. Sealing of the oral part prevented intake of maintenance medium, and strongly depress the oral release of enzymes as well. The flukes with closed oral sucker nevertheless inactivated the added host proteases of similar degree to non-sealed ones. Heatinactivated (80°C for 15 min) parasites and incubation media also were able to depress bovine protease activity. The experimental observations support the conclusion that inactivation of host proteases by the liver fluke is due primarily to protease inhibitors produced and released by the parasite. It appears that the oral opening of the liver fluke plays no notable role in inhibitor release. References AN SARI, A.A. - KHAN, M.A. - GHATAK, S. (1976): Ascaridia galli: Trypsin and chymotrypsin inhibitors. - Exp. Parasit. , 39. 74-83. BARMAN, T.E. (1969): Enzyme Handbook. - Berlin-Heidelberg-New York, Springer Verlag, pp. 928. BRAND, T. von (1973): Biochemistry of parasites. - New York-London, Academic Press. HALTON, D.W. (1967): Observation on the nutrition of digenetic Trematodes. - Parasit., 57. 639-660. HUMMEL, B.C.W. (1959): A modified spectrophotometry determination of chymotrypsin, trypsin and thrombin. - Canad. J. of Biochem. and Physiol. , 37. 1393-1399. JUHÁSZ, S. (1979): Proteolytic enzymes and enzyme inhibitors of Ascaris suum. I. The proteolytic enzymes and enzyme inhibitors of the intestine. - Acta Vet. Acad. Sei, Hung., 27. 83-87. LOCATELLI, A. - BERETTA, C. (1969): Detection of aminoacid N in saline or serum media incubated with Fasciola hepatica and proteolytic activity exerted by liver fluke "in vitro". Arch. Vet. Ital., 20. 385-391. KASSAI, T. - TÓTH, B. (1969): Inhibitory effect of worm metabolic antigen on the proteolytic activity of intestinal fluid. - Parasit. Hung., 2. 39-44.
