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Abstract
Phospholipase A2 (PLA2) is an enzyme for releasing fatty acids from the sn-2 position of a phospholipid (PL). Fatty acids released from dietary PLs are absorbed and sequestered into tissue PLs. Cellular PLA2 releases arachidonic acid, precursor for synthesis of prostaglandins (PGs) which serve many biological functions in vertebrates and invertebrates.
I report on the presence of arachidonic acid in primary screwworms, Cochliomyia hominivorax, and in secondary screwworms, Cochliomyia macellaria. Arachidonic acid appears to be accumulated during the larval stages in both species. I characterized PLA2 from the primary screwworm midgut. The screwworm midgut PLA2 is sensitive to incubation conditions, prefers high pH, and depends on calcium for optimal activity. Its activity increased with increasing protein and substrate concentration and was inhibited by the presence of oleyloxyethylphosphorylcholine.
Primary screwworm tissues are capable of biosynthesizing at least four types of PGs; PGA2, PGD2, PGE2, PGF 2α, and the enzymes for the synthesis are stable at low temperature. PG biosynthesis activity by screwworm tissues does not require the co-factors required in mammalian preparations, and prefers lower pH. PG biosynthetic activity increased with increasing protein and substrate concentration. PG synthesis was recorded as early as 15 seconds after initiating the reactions and activity was inhibited by the presence of indomethacin. I hypothesized that screwworms secrete PGs onto their host tissues to attenuate hosts' immune defense during parasitization. Using GC/MS and flourometric HPLC, I detected PGs in screwworm tissues and in their diet.
