AA assays

A particularly useful preparation of DHA, described by Ohmori and Takagi, uses oxygen oxidation over a charcoal catalyst (6). The use of oxygen and charcoal to convert AA to DHA is a well-known reaction that has been used in AA assays for many years. The oxidation can be made in ethanol, methanol, water, or various mixtures of these solvents. We carry out this procedure as follows ... 

Both in homogeneous and heterogeneous AA assays, a large excess... 

In AM procedures, however, the relative potency (i.e., the molar concentrations yielding an identical bound/free ratio) of cross-reactants or competitors is important since antibodies are not present in excess. The apparent affinity constants determine to a large degree the maximum specificity attainable. Cross-reactants usually bind less avidly than the specific antigen. Consequently, AM-type procedures are often more specific than AA assays. 

AA assays have inherently a potential detectability several orders of magnitude higher than AM asssays. 

AM assays have an intrinsically higher specificity than AA assays. 

Monoclonal antibodies have a high positive impact on specificity of AA assays. 

The use of two different antisera in sandwich methods may increase specificity in AA assays. 

AA assays are faster than AM assays at their limiting detectabilities due to the excess of antibodies in AA assays and to the law of mass action. 

The detectability of AM assays is not better than that of saturation analysis RIA, in contrast to AA assays. 

The enzymes used in the AA-assays can also be used for solid-phase AM-assays. 

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

A number of pharmaceutical substances official in BP (1993) can be assayed by adopting the above procedures of AAS as detailed in the following Table 26.1. 

Pollitt SK, Pallos J, Shao J, Desai UA, Ma AA, Thompson LM, Marsh JL, Diamond MI (2003) A rapid cellular FRET assay of polyglutamine aggregation identifies a novel inhibitor. Neuron 40(4) 685-694 Ranganathan S, Bowser, R (2003) Alterations in G(l) to S phase cell-cycle regulators during amyotrophic lateral sclerosis. Am J Pathol 162(3) 823—835... 

In a related assay, a hydroxyl value is determined for a fixed oil. A 1 3 mixture of AA in pyridine is used in the determination the pyridine is present as a catalyst. The hydroxyl value may be defined as ... 

AAS is used in a number of limit tests for metallic impurities, e.g. magnesium and strontium in calcium acetate palladium in carbenicillin sodium and lead in bismuth subgallate. It is also used to assay metals in a number of other preparations zinc in zinc insulin suspension and tetracosactrin zinc injection copper and iron in ascorbic acid zinc in acetylcysteine lead in bismuthsubcarbonate silver in cisplatinum lead in oxyprenolol aluminium in albumin solution and calcium, magnesium, mercury and zinc in water used for diluting haemodialysis solutions. 

Qualitatively interpreted assays such as mucopolysaccharide electrophoresis (MPS-EP), urinary organic analysis and amino acid thin-layer chromatography (AA-TLC) are extremely important in biochemical genetics and yet are difficult to quality control. Some useful control measures often used include ... 

Some important assays commonly used in biochemical genetics laboratories do not provide quantitative data (e.g. MPS-EP, qualitative urinary organic acid analysis, AA-TLC). In addition, all successful investigations depend heavily upon selection of the correct analytes to measure and the appropriate interpretation of the quantitative or qualitative results in their clinical context. These challenges suggest a requirement for external quality assessment or proficiency testing schemes that can inform participants about their performance in these areas when compared with other centres. 

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