Pyrophosphatase activation

For many biosynthetic reactions that liberate pyrophosphatase activity makes the process more favorable energetically, tending to make these reactions irreversible. In plants, this enzyme is present in plastids but absent from the cytosol. As a result, the cytosol of leaf cells contains a substantial concentration of PP,— enough ( 0.3 him) to make reactions such as that catalyzed by UDP-glucose pyrophosphorylase (Fig. 15-7) readily reversible. Recall from Chapter 14 (p. 527) that the cytosolic isozyme of phosphofructokinase in plants uses PPi, not ATP, as the phosphoryl donor. 

Third, the quantitative differences in concentration of the four enzymes vary appreciably therefore making several venoms an undesirable source of exonuclease (5). All partially purified preparations of venom exonuclease exhibit adenosine triphosphate-pyrophosphatase activity (cleavage of the a-/3 linkage). Pfleiderer and Ortanderl (14a) studied this issue and showed that during purification the ratio of the two activities remains constant, concluding that both activities are intrinsic properties of the same enzyme. 

Escherichia coli can he adapted to grow on PPi as the sole source of phosphorus in this situation the cells are dependent upon intracellular inorganic pyrophosphatase activity to make Pi available. To avoid possible confusion from the inducible alkaline phosphatase of E. coli, which also has pyrophosphatase activity (see Chapter 17, by Reid and Wilson, this volume), all mutant isolation studies began with an E coli strain unable to synthesize this inducible protein. 

Glycerolphosphatase and pyrophosphatase activities increased during germination. The optimal pH for these enzymes was pH 5.6 and 5.0, respectively, and the optimal temperature was 45 °C. Both enzymes were be inhibited by fluoride (Chandrasekhara and Swaminathan, 1954). 

Kj = 6.2 x 10-5Af) but inhibition is normally not evident because of pyrophosphatase activity. 

Adenylate cyclase has been obtained in soluble form from bacteria [12,13], and can be prepared free of contaminating phosphodiesterase, ATPase (adenosine triphosphatase) and pyrophosphatase activities, but the relationship of the bacterial enzyme to the enzyme found in higher forms of life is not yet clear. The bacterial enzyme, for example, does not respond to mammalian hormones or sodium fluoride. 

Shipkova M, Franz J, Abe M, Klett C, Wieland E, Andus T (2011) Association between adverse effects under azathioprine therapy and inosine triphosphate pyrophosphatase activity in patients with chronic inflammatory bowel disease. Ther Drug Monit 33 321-328... 

Murabe, Y. and Sano, Y., Thiamine pyrophosphatase activity in the plasma membrane of microglia, Histochemistry, 71,45, 1981. 

Skidmore, J. R., and Trams, E. G., Nucleotide pyrophosphatase activity of rat liver plasma membranes. Biochim. Biophys. Acta 219, 93-103 (1970). 

Yoshida, H., Fukui, S., Yamashina, 1., Tanaka, T., Sakano, T., Usui, T., Shimotsuhi, T., Yabuuchi, H., Owada, M., and Kitagawa, T., Elevation of nucleotide pyrophosphatase activity in skin fibroblasts from patient with Lowe s syndrome. Biochem. Biophys. Res. Commun. 107, 1144-1150 (1982). 

Argininosuccinate synthetase (the second enzyme of the cycle) and the remaining two enzymes of the cycle are located in the cytoplasm. Argininosuccinate synthetase catalyzes the condensation of citrulline with aspartate to form argininosuccinate. The reaction requires one molecule of ATP, which is hydrolyzed to AMP and PPi. Pyrophosphate is a strong inhibitor of the reaction (K, = 6.2 x 10 M), but inhibition is normally not evident because of pyrophosphatase activity. 

Sano, S., Matsuda, Y., and Nakagawa, H., 1988. Type B nucleoside-diphos-phatase of rat brain. Purification and properties of an enzyme with high thiamin pyrophosphatase activity. European Journal of Biochemistry. 171 231-236. 

Liu M-Y, Le Gall J. 1990. Purification and characterization of two proteins with inorganic pyrophosphatase activity from Desulfovibrio vulgaris rubrerythrin and a new, highly-active, enzyme. Biochem Biophys Res Commun 171 313-318. 

Membrane-bound 2-acetamido-2-deoxy-a- and -)8-D-galactosyltransferases from guinea-pig microsomes were able to catalyse the formation of the nonreducing, terminal residues of Forssman hapten and globoside, respectively. The enzymes can be readily differentiated, since the a-transferase is inhibited, and the -transferase is stimulated, by UDP UDP-D-glucose can suppress both a-transferase and pyrophosphatase activities. 

The enzyme is quite specific for CMP-p-NeuSAc and is distinct from nonspecific phosphodiesterase of nucleotide pyrophosphatase activities which do not cleave CMP-Neu5Ac. It may thus be considered as a p-sialidase, CMP-Neu5Ac being the only known natural sialic acid glycoside in p-linkage (Haverkamp et al. 1979 b). 

Dick and Tabatabai " have described an assay for inorganic pyrophosphatase activity in soils based on a specific colorimetric determination of extracted orthophosphate after its release from inorganic pyrophosphate (0.05M) incubated with soils for 5h at 37°C. Soil suspensions were buffered at pH 8.0. In the absence of toluene, the amounts of orthophosphate released g soil were proportional to incubation time (up to 7h), and for a given time to the amounts of soil added. Activities were unaffected by toluene addition to soils and toluene was omitted from the recommended assay procedure. 

DICK W.A. and TABATABAI M.A. 1978. Inorganic pyrophosphatase activity of soils. Soil Biology and Biochemistry, 1, 59-65. 

A kinetic study on the activation of deoxyribonuclease I by magnesium has shown that the activation curve is biphasic (the substrate being the Mg salt of bovine spleen DNA). This indicates that activation occurs at two sites on the protein. Free Mg + was required for enzyme activity, confirming that a metallo-enzyme as well as a metallo-substrate is necessary for deoxyribonuclease I activity. In contrast, it has been shown that the pyrophosphatase activity of bovine brain alkaline phosphatase depends on Mg + bound to the enzyme but not on the formation of a magnesium-substrate complex. 

Meek, G. A., and Bradbury, S., 1963, Localization of thiamine pyrophosphatase activity in the Golgi apparatus of the mollusk. Helix aspersa, J. Cell Biol. 18 73. 

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