The activity of acid proteases hydrolysing haemoglobin in parasitic helminths with special reference to interspecific and intraspecific distribution

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Abstract
SUMMARY: Acid proteases hydrolysing haemoglobin, first described by Timms & Bueding (1959), were studied to investigate the interspecific and intraspecific distribution in adult parasitic helminths. Acid protease activity was detected in a variety of adult helminths, irrespective of their habitats, namely, parasitic nematodes,Angiostrongylus cantonensis, Dirofilaria immitis, Trichuris murisandAscaris suum, a trematode,Paramphistomumsp. and cestodes,Diphyllobothrium erinaceiandHymenolepis nana. Much higher specific activity was observed in the blood nematodes,A. cantonensisandD. immitisthan in the gastro-intestinal helminths examined. The intraspecific distribution of the acid protease activity within organs was studied in those nematodes from which the organs could be anatomically separated. The highest specific activity was observed in the intestine ofA. cantonensis, D. immitisandA. suum. The activity was also found in other organs of these nematodes, namely, the reproductive organs and the body wall, but to a much lesser extent. The pH optima for the hydrolysis of haemoglobin were found to be in the pH range of 3·1 to 4·6. Each of the enzyme solutions from the 7 species of helminths hydrolysed haemoglobin faster than the other proteins examined but some activity on myoglobin, casein, albumin and other proteins was demonstrated. Pepstatin, a potent inhibitor of carboxyl proteases, inhibited the hydrolysis of haemoglobin by the acid proteases of the 7 species of the parasites. Acid protease activity fromA. cantonensisandA. suumwas not inhibited in the presence of thiol-, serine- and metallo-protease inhibitors at a concentration of 10−6M. This fact, together with the inhibitory effect of pepstatin, suggests that the enzyme activity is likely to be due to carboxyl protease(s). Acid proteases such as cathepsin D and pepsin were simultaneously used for comparison of some enzymological characteristics. The substrate specificity of the enzyme solutions from the helminths seemed to resemble that of cathepsin D rather than that of pepsin. The effects of pH and pepstatin on the acid protease activity of the helminths were similar to those on pepsin and cathepsin D.