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Two groups of acetylcholinesterase isoenzymes, which differed markedly in apparent molecular weight and subcellular distribution, were extracted from homogenates of Nippostrongylus brasiliensis. A low molecular weight (61 000) group was present predominantly in the supernatant fraction. Efficient extraction of the high molecular weight (980 000) group, which was associated only with the membrane fraction, depended upon the presence of detergent and a raised ionic strength in the homogenisation buffer. No acetylcholinesterase with the characteristics of the latter group has previously been reported from a nematode.

Treatment of rats infected with Nippostrongylus brasiliensis with a single, oral therapeutic dose of the anthelmintic benzimidazole carbamates oxfendazole or mebendazole resulted, 24 hr later, in a marked reduction (60–90%) in the secretion of a low molecular weight acetylcholinesterase from the parasites when they were incubated in vitro . This effect coincided with the expulsion of parasites from the host as a result of the therapy. When parasites were incubated in vitro with 0.1 mM oxfendazole, mebendazole, flubendazole, parbendazole, cambendazole or thiabendazole a similar effect was observed; with oxfendazole and mebendazole the effect was apparent within 1 hr and lasted for at least 4hr after removal to fresh, drug-free medium. Whether treated in the host or in vitro the reduction in secretion was balanced by an equivalent rise in acetylcholinesterase activity within the parasites. It is suggested that the inhibition of protein secretion may be a specific manifestation of a general effect of these compounds on microtubule function.

The schistosomicide 1,7-bis( p -aminophenoxy)heptane (153C51) stabilised mouse erythrocytes and rat liver lysosomes against osmotic lysis. Chloroquine was less potent in either system in terms of the maximum stabilisation achieved or the concentration needed to produce the maximum effect. Two lysosomal enzymes, acid phosphatase and β-acetylglucosaminidase, were partially inhibited by 153C51. Binding of [ 3 H]-153C51 by rat liver lysosomes was directly proportional to the drug concentration. The results are discussed in relation to the amphiphilic, cationic properties of the drug molecule and the effect of 153C51 on lysosomes in the tegument of the blood fluke Schistosoma mansoni .

1. 1. A preparation of rat brain was used to develop a quick and simple radiometric assay for 4-aminobutyrate: 2-oxoglutarate aminotransferase (GABA-T), an important enzyme in neural tissue of vertebrates and invertebrates. 2. 2. Application of the methodology to the parasitic nematode Nippostrongylus brasiliensis revealed that a soluble preparation of partially purified GABA-T could be recovered in high yield. 3. 3. This enzyme had a specific activity comparable to that observed in rat brain after similar treatment, was very stable when frozen, depended for activity upon tightly-bound pyridoxal 5-phosphate, had an apparent molecular weight of 72,000 and was strongly inhibited by NaCl. 4. 4. The inhibition was competitive with 4-aminobutyrate ( K = 20 M ) but uncompetitive with 2-oxoglutarate ( K = 160 mM ).