Triphosphatase Tripolyphosphatase, EC

Only earlier data (Meyerhof et al, 1953 Kornberg, 1957b) are available for trimetaphosphate hydrolase (EC 3.6.1.2) catalysing the following reaction  

Many enzymes, however, were demonstrated to catalyse the reaction  

there are inorganic pyrophosphatases (EC 3.6.1.1) which can hydrolyse tri- and tetraphosphate (Baykov et al, 1999). The ability of some pyrophosphatases to split these substrates depends on pH and divalent cations (Baykov et al, 1999). The most effective hydrolysis of low-molecular-weight PolyPs was observed for inorganic pyrophosphatase isolated from the archaeon Metanotrix soehgenii. This hydrolyses PolyP3 and PolyP4 for 44 and 8 %, respectively, of the PP, hydrolysis rate (Jetten et al, 1992) and may therefore be involved in their metabolism. 

Secondly, adenosylmethionine synthetase, in addition to synthetase reaction, catalyses tripolyphosphatase reactions stimulated by adenosylmethionine. Both of the enzymatic activities of the enzyme, which has been purified to homogeneity from E. coli, require a divalent metal ion and are markedly stimulated by certain monovalent cations (Markham et al, 1980). Tripolyphosphatase activity is also associated with S-ade nosy I methionine synthetase isozymes from rat liver (Shimizu et al, 1986). 

Thirdly, some RNA triphosphatases possess a weak tripolyphosphatase activity, and PolyP3 is a potential competitive inhibitor (Yu et al, 1997 Gong and Shuman, 2002). 

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