Group-specific reagents

Herbicidal Inhibition of Enzymes. The Hst of known en2yme inhibitors contains five principal categories group-specific reagents substrate or ground-state analogues, ie, rapidly reversible inhibitors affinity and photo-affinity labels suicide substrate, or inhibitors and transition-state, or reaction-intermediate, analogues, ie, slowly reversible inhibitors (106). 

In spite of numerous advances in the field of detection there are not and never have been any genuinely substance-specific chemical detection reactions. This means that, unlike the spectrometric methods, the methods of detection normally employed in chromatography cannot be employed for an unequivocal identification of compounds, they can only provide more or less definite indications for the characterization of the separated substances. Universal reagents are usually employed for a first analysis of the separation of samples of unknowns. This is then followed by the use of group-specific reagents. The more individual the pieces of information that can be provided from various sources for a presumed substance the more certainly is its presence indicated. However, all this evidence remains indicative it is not a confirmation of identity. 

Then follows a selection of group-specific reagents, in response to requests from practical workers after the publication of Volume 1 a. This part should be seen in reference to the monographs that follow or have already been published. 

These few questions serve to demonstrate that there must be great interest in characteri2dng chemical compounds by means of their reactive functional groups. The most important group-specific reagents for postchromatographic derivatization are listed alphabetically in Table 4 below ... 

If a group-specific reagent is now used, e.g. one that is chosen to react specifically with the reducing properties of aldehydes (ammoniacal silver nitrate solution) or to react with ketones (2,4-dinitrophenylhydrazine [9]) it is very simple to determine which form of alcohol is present in the sample. 

Group-specific reagents can provide evidence to characterize the substance,... 

For functionalization of S-layer-coated liposomes, the S-layer lattice was stabilized by cross-linking the S-layer subunits with either periodate-oxidized raffinose or bis(sulfo-succinimidyl) suberate (BS ). Both are amine group-specific reagents that were large and... 

There are many ligands and group-specific reagents that have been demonstrated to alter the properties of H,K-ATPase, and which are not clinically useful. For example, there is a variety of chemicals that have been used in studies on structure-function relations of H,K-ATPase and that inhibit the enzyme in vitro by modification of its amino [49,67,158], sulfhydryl [95,165,166] or carboxyl groups [140]. 

Influence of substrates and inhibitors on reactivity towards group-specific reagents The first evidence suggesting the involvement of a conformational change in the... 

Effects of group-specific reagents on transport activity and regulation of plasma membrane Na /H exchangers... 

Further evidence that carboxyl groups are important for transport activity was provided by Igarashi and Aronson [22], Friedrich et al. [23], and Kinsella et al. [24] using the carboxyl group-specific reagent, A,A -dicyclohexylcarbodiimide (DCCD). DCCD irreversibly inactivated the brush border Na /H exchanger in rabbit and... 

Labelling of proteins with group specific reagents... 

Affinity labels are molecules that are structurally similar to the substrate for the enzyme that covalently modify active site residues. They are thus more specific for the enzyme active site than are group-specific reagents. Tosyl-l-phenylalanine chloromethyl ketone (TPCK) is a substrate analog for chymotrypsin (Figure 8.21). TPCK binds at the active site and then reacts irreversibly with a histidine residue at that site, inhibiting the enzyme. The compound 3-bromoacetol is an affinity label for the enzyme triose phosphate isomerase (TIM). It mimics the normal substrate, dihydroxyacetone phosphate, by binding at the active site then it covalently modifies the enzyme such that the enzyme is irreversibly inhibited (Figure 8.22). 

Figure 8.19. Enzyme Inhibition by Diisopropylphosphoflnoridate (DIPF), a Group-Specific Reagent. DIPF can...

Figure 8.20. Enzyme Inactivation by lodoacetamide, a Group-Specific Reagent. lodoacetamide can inactivate an enzyme by reacting vv ith a critical cysteine residue.

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