Alkaline phosphatase transferase activity

Murphy et al. (1964) found increased activities of alkaline phosphatase in livers of rats exposed to 35 ppm formaldehyde for 18 hours and suggested that formaldehyde may be hepatotoxic. More recent animal studies, however, have found no consistent evidence for formaldehyde-induced hepatotoxicity. Woutersen et al. (1987) found statistically significant increased levels of aspartate amino transferase, alanine amino transferase, and alkaline phosphatase in plasma of rats exposed to 20 ppm, (but not to 10 or 1 ppm) 6 hours/day, 5 days/week for 13 weeks, but found no exposure-related microscopic lesions... 

The answer is c. (Katzung, p 933.) Resistance to thioguanine occurs because of an increase in alkaline phosphatase and a decrease in hypoxanthine-guanine phosphoribosyl transferase. These enzymes are responsible, respectively, for the increase in dephosphorylation of thiopurine nucleotide and the conversion of thioguanine to its active form, 6-thioinosinic acid. 

Exposure of male Fischer 344 rats to ptzra-xylene (0-1600 ppm [0-6940 mg/m- ], 6 h per day for one or three days) had negligible effect on hepatic morphology and serum activities of alanine or aspartate aminotransferases, lactate dehydrogenase, ornithine carbamyl transferase, alkaline phosphatase or serum bilirubin concentration (Simmons et al., 1991). Liver size was increased and its cytochrome P450 content was elevated. 

More recently, isotopic labeling experiments have assumed a major role in establishing the detailed mechanism of enzymic action. It was shown that alkaline phosphatase possesses transferase activity whereby a phos-phoryl residue is transferred directly from a phosphate ester to an acceptor alcohol (18). Later it was found that the enzyme could be specifically labeled at a serine residue with 32P-Pi (19) and that 32P-phosphoserine could also be isolated after incubation with 32P-glucose 6-phosphate (20), providing strong evidence that a phosphoryl enzyme is an intermediate in the hydrolysis of phosphomonoesters. The metal-ion status of alkaline phosphatase is now reasonably well resolved (21-23). Like E. coli phosphatase it is a zinc metalloenzyme with 2-3 g-atom of Zn2+ per mole of enzyme. The metal is essential for catalytic activity and possibly also for maintenance of native enzyme structure. 

We have already seen a number of models for the zinc(II) containing enzymes such as carbonic anhydrase in Section 11.3.2. Zinc is an essential component in biochemistry, and forms part of the active site of more then 100 enzymes, of which hydrolases (such as alkaline phosphatase and carboxypeptidase A), transferases (e.g. DNA and RNA polymerase), oxidoreductases (e.g. alcohol dehydrogenase and superoxide dismutase) and lysases (carbonic anhydrase) are the most common. In addition, the non-enzyme zinc finger proteins have an important regulatory function. In many of these systems, the non-redox-active Zn2+ ion is present as a Fewis acidic centre at which substrates are coordinated, polarised and hence activated. Other roles of zinc include acting as a template and playing a structural or regulatory role. 

Severe overdosage of sodium aurothiopropanol sulfonate (1.1 g daily for 13 days) caused jaundice and skin eruptions. Liver biopsies showed modest centrilobular necrosis and significant bile stasis. Serum hepatic enzyme activities were increased. The patient was treated with dimercaprol and recovered after 2 months, although alkaline phosphatase and gamma-glutamyl-transferase activities remained high for 6 months. 

There are five enzymes that are commonly used in diagnosis of liver disease Aspartate aminotransferase (AST EC 2.6.1.1), alanine aminotransferase (ALT EC 2.6.1.2), alkaline phosphatase (ALP 3.1.3.1), and y-glutamyl transferase (GGT EC 2.3.2.2), are commonly used to detect liver injury, and lactate dehydrogenase (LD EC 1.1.1.27) is occasionaEy used. ALT and GGT are present in several tissues, but plasma activities primarily reflect liver injury. AST is found in liver, muscle (cardiac and skeletal), and to a liipited extent iti fed cells. LD has wide tissue distribution, and is thus relatively nonspecific. ALP is found in a number of tissues, but in normal individuals primarEy reflects bone and liver sources. Thus based on tissue distribution, ALT and GGT would seem to be the most specific markers for liver injury. 

Proximal tubule cells in culture should have retained functional attributes such as (1) polar architecture and junctional assembly of epithelia and correct membrane distribution of enzymes and transport systems (2) vectorial transport of solutes and water, manifested by the formation of domes when cultured on solid supports [81] and the generation of transepithelial electrophysiological properties [82, 83] due to the expression of proximal tubule specific claudins 2- and 10 [84, 85] (3) cellular uptake of xenobiotics from either the apical or basolateral side, as observed in vivo and (4) expression of nephron segment-specific characteristics, i.e., distinct expression of differentiation markers, metabolic and transport properties, and hormone responsiveness. Such markers include the expression of the brush border enzymes alkaline phosphatase, leucine aminopeptidase, and y-glutamyl transferase [4, 86], In addition, proximal tubule cells should possess Na+,K+-ATPase activities, Na+-dependent glucose, and p-aminohippurate transport. Proximal tubule cells increase cAMP levels in response to parathyroid... 

The consumption of approximately 10 g of ethyl alcohol by a healthy person is without significant effect on serum alkaline phosphatase activities (S60). More substantial ethanol ingestion (approximately 0.75 g/kg body weight/day for 3 consecutive days) also produces no change in serum alkaline phosphatase values, although serum alanine aminotransferase and serum 7-glutamyl transferase activities rise significantly under these conditions (F21). 

Several enzymes bind both magnesium and zinc ions, using them for different purposes. For example, nucleotidyl transferases can use one metal ion, to which is coordinated a phosphate group and a carboxylate group, the latter serving to polarize the water nucleophile. When there are two metal ions present, the carboxylate group also binds the second metal ion which in turn activates the nucleophile. Therefore it appears that the second metal ion aids in the catalysis, replacing the action of an active-site side chain in those enzymes of that activity that only bind one metal ion. T vo enzymes will be described here—the alkaline phosphatase and the 3 -5 exonuclease from E. coli. 

PXR, in the presence of a CYP3A4 inducer, binds to and activates the responsive elements in a reporter gene construct, leading to higher expression of a reporter gene, which is usually luciferase, chloramphenicol acetyl transferase (CAT), or secretory placental alkaline phosphatase (SPAP). The expression of the reporter gene is determined, and the ratio between the treatment and vehicle control is used to estimate human PXR-dependent induction potential of the test compound. 

Cocoa powder exerted anticancer properties in in vivo studies. Amin et al. [50] indicated that cocoa liquor extract lowered the activity of tumor marker enzymes (alkaline phosphatase, gamma-glutamyl transpeptidase, glutathione-S-transferase, and glutathione reductase activities) in plasma and/or liver of hepatocarcinogenic male Sprague-Dawley rats, which were induced with diethylnitrosamine and 2-acetylaminofluorene. 

In a second study, the effect of oxcarbazepine monotherapy for 18 months on bone turnover was longitudinally explored in 34 newly diagnosed prepubertal and pubertal children [227 ]. The serum concentrations of 25-hydroxycolecalciferol were significantly reduced by oxcarbazepine, while osteocalcin and gamma-glutamyl transferase activity were significantly increased compared with baseline values. Phosphorus, parathyroid hormone, and calcitonin concentrations and alkaline phosphatase activity increased non-significantly. In three patients who had... 

Liver A 66-year-old man developed acute cholestatic hepatitis after receiving intravenous ciprofloxacin for 3 days for gastroenteritis all other cause of hepatitis were excluded and alkaline phosphatase and gamma-glutamyl transferase activities returned to normal within 3 months of ciprofloxacin withdrawal [40 ]. 

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