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Apyrases or ATP diphosphohydrolases (ATPDases: EC 3.6.1.5) first mentioned by Meyerhof in 19451 refer to a family of enzymes that catalyse the hydrolysis of the γ and β phosphate residues of triphospho- and diphosphonucleosides. The original report by Kalckar in 19442 of an ATPDase in potato extracts initiated a series of studies on this enzyme (for reviews see 3, 4). Two isoforms have been described from Solanum tuberosum, varieties Desiree and Pimpernel respectively5. ATPDases were later found in other plant tissues: cabbage leaves, clover seeds, pea plumules, chick-pea roots, Alaska pea stems, Mimosa pudica pulvinius and yellow lupin cotyledons3, 4. The role of ATPDases in plants has not yet been clearly defined but an implication in starch synthesis has been proposed6. ATPDases have been reported in invertebrates including hematophagous insects, ticks and leeches (for reviews see 3, 4 and 7) and in a parasitic worm8. In most of these species, ATPDases would act as antiplatelet agents preventing blood clotting3, 7. The enzyme also exists in prokaryotes9–11, among them, a virulent Shigella where it is localised in the periplasmic space. It the latter case, it was suggested that the ATPDase plays the role of a general cytotoxin involved directly or indirectly in the actual killing of the host cells11. |
