An acid phosphatase (AP) and a phosphorylcholine hydrolase (PCH) were detected in excretory–secretory (ESP) products from adult Haemonchus contortus. The AP had a pH optimum of 4.5 and was inhibited by tartaric acid and sodium fluoride, but not by o-phenanthroline. The AP hydrolyzed paranitrophenol (pnp)-phosphate and to a lesser extent pnp-phenylphosphonate but did not hydrolyze diester substrates. Purified AP consisted of heterodimers with relative molecular weight (Mr) of 41.9 and 48.7 kDa and had a native molecular weight of 98 kDa by size-exclusion chromatography (SEC). The PCH had a pH optimum of about 9.5 and was inhibited by EDTA and o-phenanthroline but not by the specific phospholipase inhibitor D609. The specific activity of PCH in the ESP was aproximately 25-fold less than that of AP. PCH also hydrolyzed 5′-thymidine monophosphate-pnp at a rate about 40% lower than pnp-phosphorylcholine but did not hydrolyze 3′-thymidine monophosphate-pnp. Partial purification of PCH suggests an Mr of 50.2 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an Mr of 102 kDa by SEC. Both AP and PHC were secreted in vitro in a time-dependent manner and had their highest concentrations in the intestine. The results indicate that H. contortus adults secrete significant amounts of AP that might be a digestive enzyme. PCH is also an intestinal enzyme and is secreted in lesser amounts than AP. The PCH is probably not a phospholipase C but has some characteristics of a type I phosphodiesterase.

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