Enzyme systems, linked

Plants have an enzyme system linking the oxidation of,glutathione to the reduction of dehydroascorbic acid. A similar enzyme may occur in animal tissues, although in this case a facile non-en matic reaction could possibly account for the observed activity. The plant eni me provides a... 

Pinally, the methylation pathway could represent an enzymic system linked to the source of choline in brain. It is known that the choline moiety as such cannot pass into the brain from the blood stream, but rather a lipid-choline moiety, probably lysophosphati-dylcholine, might be involved in the transport of the base. The methylation pathway, however, can be visualized as another means of producing choline in brain, provided Ptd-ethanolamine is transported into the brain. Conversely, due to the noticeable presence in the brain tissue of free serine, a possible pathway for choline production in brain may be represented by an exchange reaction between free serine and endogenous brain phospholipids, 9 20 cessive decarboxylation of phosphatidyl serine to Ptd-ethanolamine in the same tissue, finally followed by the described methylation reactions to produce a definite pool of active Ptd-choline,... 

Because of its position in the Periodic Table, molybdenum has sometimes been linked to chromium (see Chromiumand chromium alloys) or to other heavy metals. However, unlike those elements, molybdenum and its compounds have relatively low toxicity, as shown in Table 3. On the other hand, molybdenum has been identified as a micronutrient essential to plant life (11,12) (see Fertilizers), and plays a principal biochemical role in animal health as a constituent of several important enzyme systems (see Mineral nutrients). 

Biomedical Applications. TRIS AMINO is used for a number of purposes in its pure form, it is an acidimetric standard the USP grade can be utilized intraveneously for therapeutic control of blood acidosis TRIS AMINO also is useful in genetic engineering as a buffering agent for enzyme systems, industrial protein purification, and electrophoresis. AMP has found use as a reagent in enzyme-linked immunoassays. The primary appHcation is for alkaline phosphatase assays. 

The TCAs, such as amitriptyline (Elavil) and dox-epin (Sinequan), inhibit reuptake of norepinephrine or serotonin at the presynaptic neuron. Drug classified as MAOIs inhibit the activity of monoamine oxidase a complex enzyme system that is responsible for breaking down amines. This results in an increase in endogenous epinephrine, norepinephrine and serotonin in the nervous system. An increase in these neurohormones results in stimulation of the CNS. The action of the SSRIs is linked to their inhibition of CNS neuronal uptake of serotonin (a CNS neurotransmitter). The increase in serotonin levels is thought to act as a stimulant to reverse depression. 

Enzyme linked electrochemical techniques can be carried out in two basic manners. In the first approach the enzyme is immobilized at the electrode. A second approach is to use a hydrodynamic technique, such as flow injection analysis (FIAEC) or liquid chromatography (LCEC), with the enzyme reaction being either off-line or on-line in a reactor prior to the amperometric detector. Hydrodynamic techniques provide a convenient and efficient method for transporting and mixing the substrate and enzyme, subsequent transport of product to the electrode, and rapid sample turnaround. The kinetics of the enzyme system can also be readily studied using hydrodynamic techniques. Immobilizing the enzyme at the electrode provides a simple system which is amenable to in vivo analysis. 

Because LCEC had its initial impact in neurochemical analysis, it is not, surprising that many of the early enzyme-linked electrochemical methods are of neurologically important enzymes. Many of the enzymes involved in catecholamine metabolism have been determined by electrochemical means. Phenylalanine hydroxylase activity has been determined by el trochemicaUy monitoring the conversion of tetrahydro-biopterin to dihydrobiopterin Another monooxygenase, tyrosine hydroxylase, has been determined by detecting the DOPA produced by the enzymatic reaction Formation of DOPA has also been monitored electrochemically to determine the activity of L-aromatic amino acid decarboxylase Other enzymes involved in catecholamine metabolism which have been determined electrochemically include dopamine-p-hydroxylase phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase . Electrochemical detection of DOPA has also been used to determine the activity of y-glutamyltranspeptidase The cytochrome P-450 enzyme system has been studied by observing the conversion of benzene to phenol and subsequently to hydroquinone and catechol... 

The 1-methylindole derivative (14) (see Table 7.1), which was marginally more potent than (13) in vitro, showed good oral activity in the BJ test in the rat (ED50 0.11 mg/kg). However, it potentiated the pentobarbitone sleeping time in the mouse, suggesting it had the capacity to bind to and inhibit the hepatic cytochrome P-450-linked oxidase enzyme system. Optical... 

Ranitidine, famotidine, and nizatidine do not inhibit the cytochrome P450-linked oxygenase enzyme system in the liver. 

This link (http //www.icgeb.Org/ p450srv/l is a website with various links to several research laboratories, many research papers, proposals, databases, and proceedings. In addition, it contains a list of sequences of the CYP superfamily and its homologs from different enzyme systems (273,317). 

Where drug are shown to form reactive intermediates by specific enzyme systems, it might be expected that the polymorphism or absence of these systems would track idiosyncratic reactions but to date no such link has been established. In fact, the most confounding element of idiosyncratic reactions is their unpredictable nature and whilst reactive intermediates may present a risk factor the true nature of the response is likely to be multifactorial. Changes in dmg metabolizing capacity, affecting the balance of bioactivation and bioinactivation processes which may be mediated through concomitant infection may also be a contributory factor. 

Early reports of such an enzyme system, tightly bound and occurring in a particulate fraction of mung bean, were made by Hassid and associates.292,293 The glycosyl donor was reported to be GDP-D-glucose and the product was characterized as a / -(l— 4)-linked D-glucan,292,293 Liu and Hassid294 solubilized, and partially purified, this enzyme. 

Heller and Villemez299,300 solubilized, but did not separate, the D-mannosyltransferase and D-glucosyltransferase activities from this particulate-enzyme system, and found that, when only GDP-D-mannose is provided as the substrate, a/ -(1— 4)-linked D-mannan is synthesized and, when only GDP-D-glucose is present, ap-(l— 4)-linked D-glucan is produced. They further noted, with this transferase system, that incorporation of D-glucose from GDP-D-glucose into polysaccharide is a shortlived reaction that can be greatly extended if GDP-D-mannose is also included in the reaction mixture. 

In contrast, introduction of the a-(l - 6)-linked D-glucosyl branches present in polysaccharides 10b and 12b was shown to occur readily at the level of polyprenyl oligosaccharide diphosphates. With enzymic systems from S. senftenberg289 and S. bredeney,286 D-glucosylation was found to take place prior to the polymerization reaction. In the former case, participation... 

An adenosine aminohydrolase (deaminase) is also present in many mammalian tissues. This enzyme is of great interest because hereditary deficiency of the enzyme is linked to a severe (usually fatal) defect in the immune system, marked by a serious deficiency in lymphocytes and consequent inability to combat infections. 

---