Urease reduction

Arachin, the counterpart of glycinin in peanuts, consists of subunits of 60,000—70,000 mol wt which on reduction with 2-mercaptoethanol yield polypeptides of 41,000—48,000 and 21,000 mol wt (17) analogous to the behavior of glycinin. In addition to the storage proteins, oilseeds contain a variety of minor proteins, including trypsin inhibitors, hemagglutinins, and enzymes. Examples of the last are urease and Hpoxygenase in soybeans. 

Enzymes modified with N -carbonyldiimidazole (CDI) include horseradish peroxidase 761 /1-lactamase after nitration and reduction,[771 lysozyme, and urease.[781 Ref. [77] describes how the tyrosine side chain of a protein was nitrated, reduced with dithionite to an amino group, and then treated with CDI or A/-(2,2,2-trifluoro-ethoxycarbonyl)imidazole to give the benzoxazolinonyl alanine moiety ... 

A number of copper -containing protein compounds are enzymes with an oxidase function (ascorbic acid oxidase, urease, etc 1 and these play an important role in Ihe biological oxidation-reduction system. There is a definite relationship of copper with iron in connection with utilization of iron in hemoglobin function. 

Fig. 8 Synthesis of amino acids by a multienzyme system consisting of leucine dehydrogenase (LeuDH) catalyzing the reductive amination of the corresponding keto acid, L-lactate dehydrogenase (l-LDH), and lactate for the regeneration of NADH and urease for the in situ generation of ammonia. The coenzyme NAD+ was covalently bond to dextran, enzymes and dextran-coupled NAD+ were...

The maximal intestinal immunization can be achieved by intra-Peyer s patch immunization, and thus this method can be used to screen oral vaccine candidate antigens without the added complication of simultaneously testing oral-delivery systems. Immunization of subjects against Helicobacter pylori by intra-Peyer s patch resulted in an 84-91% reduction in H. pylori infection compared with unimmrmized controls. The therapeutic efficacy of the recombinant H. pylori urease vaccine in mice was shown to be comparable with that achieved with the combined anti-biotic/antacid treatment in humans. The oral vaccination is preferred to conventional treatment of ulcers because it is a very simple and quick procedure compared with long-term conventional treatment. In addition, vaccines use the defense mechanisms of the body to establish long-lasting immunity. ... 

Urease has a molecular weight of590 000 30 000 and consists of six identical subunits. Each subunit contains two Ni ions of different valency which are involved in substrate binding and conversion. The isoelectric point of the protein is at pH 5 and the temperature optimum of the catalysis at 60°C. The kinetic constants for urea hydrolysis have been determined to be k+2 = 5870 s"1 and Km = 2.9 mmol/1. Other amides, such as formamide and semicarbazide, react much more slowly than urea. The pH optimum of urease depends on the nature of the buffer used and, with the exception of acetate buffer, equals the pJTs value of the buffer. The active center of urease contains an SH-group that is essential for the stability of the enzyme. Complexing agents, such as EDTA and reductants, are required for stabilization. 

Similar reactor configurations using flat membranes in place of hollow fibers have even been used with urease, uricase, glucose oxidase and creatinine kinase.49 An enzyme solution is, in this case, introduced into one of the membrane-separated chambers of a flat-membrane dialyzer. Operating the reactor at high feed flow rates leads to a reduction of mass transfer resistances, which can also be achieved using suitable turbulence promoters. The overall behavior of such systems appears to be similar to that of the hollow fiber enzyme reactors, except for an apparent higher efficiency.49... 

The action of ascorbic acid on many enzymes appears to be conditioned by other substances, notably metallic ions, present in reaction mixtures certainly where its action has been critically examined, this has been found to be so. Whether ascorbic acid in vivio has any regulatory influence on these enzymes is uncertain. Still more improbable is the view that this action of ascorbic acid constitutes one of its essential roles in the living cell, since it has been shown both for j3-amylase and urease that other dienols (reductone, dehydroxymaleic acid, reductic acid, hydroxy-tetronic acid) which are biologically inactive react similarly (Hanes, 1935 Mapson, 1946). 

The reduction of intestinal ammonia synthesis can also be achieved by the administration of non-absorbable disaccharides-like lactulose and lactitol or antibiotics like neomycin, paramomycin, metronidazole or rifaximin. Lactulose exerts several effects (1). acidification of the intestinal content resulting in a reduction of ammonia absorption and net movement of ammonia from the blood into the bowel and (2). reduced bacterial production of ammonia in the colonic lumen due to environmental changes with promotion of the growth of non-urease producing bacteria and (3). the cathartic effect. The daily dose of lactulose is between 30 and 60 g per day. The goal is to obtain 2-3 soft bowel movements per day. Recently lactulose has been proven to be effective even in patients with minimal HE (Prasad et al., 2007). 

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