Acid phosphohydrolase

Jones, 1990 Nishizuka 1992 and 1995). The second, more sustained inaease in DAG comes from the hydrolysis of PC by PC-specific PLC (direct-route), or indirectly via the sequmtial activation of phosphohpase D (PLD) and phosphatidic acid phosphohydrolase (PAP) to generate PA and DAG, respectively. The second phase of DAG production proceeds without an elevation in the concentration of intracellular and might be related to the activation of Ca -independent protein kinase C isoforms (Wakelam, 1998). 

In addition to PL A2-mediated mechanisms, it is worth noting that A A can also be generated from the activation of other pathways, including PLC, which forms DAG that could be cleaved to generate AA via the action of mono- or diglycerol lipase (194). PLD-mediated cleavage of phosphatidylcholine may also generate phosphatidic acid (PA), which can be further metabolized by phosphatidic acid phosphohydrolase to DAG, and activation of AA release by arARs via the PLD pathway has been reported (196). 

Roberts R, Sciorra VA, Morris AJ (1998) Human type 2 phosphatidic acid phosphohydrolases. Substrate specificity of the type 2a, 2b, and 2c enzymes and cell surface activity of the 2a isoform. J Biol Chem 273 22059-22067... 

In neutrophils, phosphatidic acid produced by PLD is then subsequently cleaved by phosphatidic acid phosphohydrolase [32]. In neu-tropohils, choline-containing phosphoglycerides contain approximately equal amounts of alkylacyl- and diacyl-glycerols. Thus the PA is dephos-phorylated to give both DAG and alkylacylglycerol. The DAG produced... 

Kanoh, H., Imai, S., Yamada, K. and Sakane, F. (1992) Purification and properties of phoyhatidic acid phosphohydrolase from porcine thymus membranes, Journal of Biological Chemistry 267, 2 309-25314... 

Fleming, I.N. and Yeaman S.J. (1995) Purification and characterisation of iV-ethylmaleimide-insensitive phosphatidic acid phosphohydrolase (PAP2) from rat hver. Biochemical Journal 308,983-989... 

Fic. 9. Comparative effect of preincubation of lysosomes before and after activation by Triton X-100, 24°C in a Dubnoff shaker saturated with lOOX oxygen. Acid phosphohydrolase activity 15 minutes after activation had dropped 75%, while the activity incubated for 15 minutes in intact organelles showed no significant change when activated by Triton X-100. Solid bar, nonactivated dotted bar, activated at time... 

Lipid phosphate phosphohydrolases (LPPs), formerly called type 2 phosphatidate phosphohydrolases (PAP-2), catalyse the dephosphorylation of bioactive phospholipids (phosphatidic acid, ceramide-1-phosphate) and lysophospholipids (lysophosphatidic acid, sphingosine-1-phosphate). The substrate selectivity of individual LPPs is broad in contrast to the related sphingosine-1-phosphate phosphatase. LPPs are characterized by a lack of requirement for Mg2+ and insensitivity to N-ethylmaleimide. Three subtypes (LPP-1, LPP-2, LPP-3) have been identified in mammals. These enzymes have six putative transmembrane domains and three highly conserved domains that are characteristic of a phosphatase superfamily. Whether LPPs cleave extracellular mediators or rather have an influence on intracellular lipid phosphate concentrations is still a matter of debate. 

Female NMRI mice were exposed to 100 ppm of hydrogen sulfide for 2 hours at 4-day intervals excitement was observed (Savolainen et al. 1980). Exposure also resulted in decreased cerebral ribonucleic acid (RNA), decreased orotic acid incorporation into the RNA fraction, and inhibition of cytochrome oxidase. An increase in the glial enzyme marker, 2, 3 -cyclic nucleotide-3 -phosphohydrolase, was seen. Neurochemical effects have been reported in other studies. Decreased leucine uptake and acid proteinase activity in the brain were observed in mice exposed to 100 ppm hydrogen sulfide for 2 hours (Elovaara et al. 1978). Inhibition of brain cytochrome oxidase and a decrease in orotic acid uptake were observed in mice exposed to 100 ppm hydrogen sulfide for up to 4 days (Savolainen et al. 1980). 

The activity of PLD on phosphatidylcholine generates phosphatidic acid, and this may be further metabolised by the enzyme phosphatidate phospho-hydrolase to form DAG (Fig. 6.19). Furthermore, the activity of DAG kinase can convert the DAG (generated either from phosphatidic acid or from the activity of PLC) back into phosphatidic acid. Both phosphatidic acid and DAG have functions as second messengers thus the activities of PLD, phosphatidate phosphohydrolase and DAG kinase all play important roles in the generation of these intracellular signalling molecules. 

The enzyme phosphatidate phosphohydrolase can be inhibited by propranolol, although this inhibitor is not completely specific. Thus, propranolol treatment of neutrophils results in the increased formation of phosphati-dic acid and the decreased formation of DAG. There is increasing evidence... 

Acid phosphatase or orthophosphoric monoester phosphohydrolase (EC 3.1 3.2) activity is widespread throughout nature. Hydrolysis of a variety of orthophosphate esters as well as transphosphorylation reactions are catalyzed by enzymes from many sources. Table I illustrates their ubiquitous nature. 

In interesting recent studies, Poliak and co-workers (67, 68) have observed glucose-6-P phosphohydrolase, acid inorganic pyrophosphatase, and PPi-glucose phosphotransferase activities to be considerably higher in lipid-poor reticulosomes than in microsomal preparations. They hypothesized that reticulosomes, which they prepared by treatment of microsomal preparations from rat and chick livers with ribonuclease and deoxycholate (68), may be the precursors of endoplasmic reticulum, and... 

Snoke and Nordlie (82, 83) have extended these studies of Duttera et al. (87) to include PPS-glucose phosphotransferase as well as glucose-6-P phosphohydrolase activity of the enzyme and have also noted essentially parallel progressive losses of both activities concomitant with release of acid-soluble phosphate resulting from phospholipase C action. A partial (fed animals) or total (fasted rats) restoration of both activities was effected by phospholipid supplementation of phospholipase-treated preparations. However, as indicated by detailed studies of catalytic properties of the various preparations, the enzyme was not restored to its... 

Detergents (26, 41, 46, 96, 97) Optimal concentrations of deoxycholate, cholate, Triton X-100, and cetyltri-methylammonium bromide activate, as does urea. Activation of phosphotransferase > that of phosphohydrolase. Supraoptimal levels inhibit, as do all tested concentrations of sodium lauryl sulfate and Tweens 20 and 80. (See also Lysolecithin, Fatty acids, and Long-chain fatty acyl-CoA esters, above)... 

MA Balboa, J Balsinde, EA Dennis. Involvement of phosphatidate phosphohydrolase in arachidonic acid mobilization in human amnionic WISH cells. J Biol Chem 273 7684-7690, 1998. 

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