Alkaline phosphatase, catalysis reaction

Affinity reagent phases, examples, 318-319 Alamethicin, response of photocurrent amplitude to step in bias potential, 60,6, 63 Alkaline phosphatase, catalysis of reaction, 305... 

Phosphates of pharmaceutical interest are often monoesters (Sect. 9.3), and the enzymes that are able to hydrolyze them include alkaline and acid phosphatases. Alkaline phosphatase (alkaline phosphomonoesterase, EC 3.1.3.1) is a nonspecific esterase of phosphoric monoesters with an optimal pH for catalysis of ca. 8 [140], In the presence of a phosphate acceptor such as 2-aminoethanol, the enzyme also catalyzes a transphosphorylation reaction involving transfer of the phosphoryl group to the alcohol. Alkaline phosphatase is bound extracellularly to membranes and is widely distributed, in particular in the pancreas, liver, bile, placenta, and osteoplasts. Its specific functions in mammals remain poorly understood, but it seems to play an important role in modulation by osteoplasts of bone mineralization. 

Currently, only a handful of examples of unique protein carboxylate-zinc interactions are available in the Brookhaven Protein Data Bank. Each of these entries, however, displays syn coordination stereochemistry, and two are bidentate (Christianson and Alexander, 1989) (Fig. 5). Other protein structures have been reported with iyw-oriented car-boxylate-zinc interactions, but full coordinate sets are not yet available [e.g., DNA polymerase (Ollis etal., 1985) and alkaline phosphatase (Kim and Wyckoff, 1989)]. A survey of all protein-metal ion interactions reveals that jyw-carboxylate—metal ion stereochemistry is preferred (Chakrabarti, 1990a). It is been suggested that potent zinc enzyme inhibition arises from syn-oriented interactions between inhibitor carboxylates and active-site zinc ions (Christianson and Lipscomb, 1988a see also Monzingo and Matthews, 1984), and the structures of such interactions may sample the reaction coordinate for enzymatic catalysis in certain systems (Christianson and Lipscomb, 1987). 

Catrina I, O Brien PJ, Purcell J et al (2007) Probing the origin of the compromised catalysis of E. coli alkaline phosphatase in its promiscuous sulfatase reaction. J Am Chem Soc 129 5760-5765... 

So far, only very little attention has been focussed on the use of zeolites in biocatalysis, i.e., as supports for the immobilization of enzymes. Lie and Molin [116] studied the influence of hydrophobicity (dealuminated mordenite) and hydrophilicity (zeolite NaY) of the support on the adsorption of lipase from Candida cylindracea. The adsorption was achieved by precipitation of the enzyme with acetone. Hydrolysis of triacylglycerols and esterification of fatty acids with glycerol were the reactions studied. It was observed that the nature of the zeolite support has a significant influence on enzyme catalysis. Hydrolysis was blocked on the hydrophobic mordenite, but the esterification reaction was mediated. This reaction was, on the other hand, almost completely suppressed on the hydrophilic faujasite. The adsorption of enzymes on supports was also intensively examined with alkaline phosphatase on bentolite-L clay. The pH of the solution turned out to be very important both for the immobilization and for the activity of the enzyme [117]. Acid phosphatase from potato was immobilized onto zeolite NaX [118]. Also in this study, adsorption conditions were important in causing even multilayer formation of the enzyme on the zeolite. The influence of the cations in the zeolite support was scrutinized as well, and zeolite NaX turned out to be a better adsorbent than LiX orKX. 

ADP and [y- P]ATP at pH 7, the unlabelied phosphate exchanges with the label under enzymic catalysis. Otherwise, the termini generated on cleavage may first be dephosphorylated with alkaline phosphatase, before end-labelling. At pH 8.6 the exchange reaction is suppressed, and only the kinase reaction for determination of 5 -hydroxy termini takes place. ... 

Many chemical reactions carried out in supercritical fluid media were discussed in the first edition, and those developments are included in total here after some recent work is described. In the epilogue (chapter 13) of the first edition we made reference to one of the author s work in enzyme catalyzed reactions in supercritical fluids that was (then) soon to appear in the literature. The paper (Hammond et al., 1985) was published while the first edition was in print, and as it turned out, there was a flurry of other activity in SCF-enzyme catalysis many articles describing work with a variety of enzymes, e.g., alkaline phosphatase, polyphenol oxidase, cholesterolase, lipase, etc., were published starting in mid 1985. Practical motivations were a potentially easier workup and purification of a product if the solvent is a gas (i.e., no liquid solvent residues to contend with), faster reaction rates of compounds because of gas-like transport properties, environmental advantages of carbon dioxide, and the like. 

Enzymes may use any of the above mentioned modes of catalysis in order to catalyze a particular chemical reaction. For example, the imidazole ring of a histidine residue of the enzyme a-chymotrypsin (Section 4.4) can function as a general-base catalyst, while in the enzyme alkaline phosphatase, the same residue can function as a nucleophilic catalyst. Indeed, enzymes are complex catalysts which employ more than one catalytic parameter during the course of their action. It is by this successful integration of a combination of individual catalytic processes that a rate enhancement as high as 10 " may be achieved. Furthermore, it is this combination of factors which results in a specific catalyst. 

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