Hapten hydroxyl

The conversion of [49] into [50] involves a Claisen rearrangement. Once this was realized it was less surprising that no specific catalytic groups on the enzyme are involved. Support for the Claisen-type mechanism comes from the inhibition shown by the bicyclic dicarboxylate [51], prepared by Bartlett and Johnson (1985) as an analogue of the presumed transition state [52], This same structure [51], coupled through the hydroxyl group to a small protein, was used as a hapten to induce antibodies, one (out of eight) of which mimics the behaviour of chorismate mutase, albeit less efficiently (Table 7). 

Many other redox reactions are potentially amenable to antibody catalysis. For example, the chemistry of the P-450 cytochromes, including the hydroxylation of alkanes and the epoxidation of alkenes, can be mimicked with synthetic porphyrins. Incorporation of such molecules into antibody active sites could conceivably yield new catalysts that combine the intrinsic reactivity of the cofactor with the tailored selectivity of the binding pocket. Work is just beginning in this area, but preliminary studies with porphyrin haptens have yielded some interesting results.126-130 Novel redox chemistry can also be anticipated for antibodies containing metal ions, flavins, nicotinamide analogs, and other reactive moieties. 

A carboxyl group can be introduced in almost any compound by various methods. In cases where a free thiol is present, the carboxyl group can be introduced easily by reaction with bromo- or iodoacetic acid. This reaction is very mild and is usually performed at pH around 8-9. When the hapten contains a hydroxyl group, carboxylic acid may be introduced by one of the following methods (a) carboxymethylation of the hydroxyl group with bromo- or iodoacetic acid (b) esterification with dicarboxylic acid anhydrides, such as succinic anhydride, to yield hemi-succinates, which are unstable above pH 9 (c) reaction with phosgene, which results in the formation of chlorocarbonates. ... 

Synthetic procedures used to prepare antigenic hapten-carrier conjugates are reviewed by Erlanger. Procedures that have proven successful with hapten molecules that possess carboxyl, amino, hydroxyl, and carbonyl groups are fairly routine. The preparation of hapten-carrier conjugates by other synthetic routes is also considered. 

The introduction of I into molecules containing tyrosyl or histidyl moieties can be carried out chemically by the Chloramine T procedure or enzymatically by lactoperoxidase." The prelabeled Bolton-Hunter reagent [A-succinimidyl 3-(4-hydroxyl-5-[ I]iodophenylpropionate] reacts under mild conditions with molecules containing amino groups (e.g., proteins and haptens) to introduce an iodinated propyltyrosyl moi-... 

The biotransformation of the toxic oil contaminant PAP to the L-tryptophan contaminant PAA may link TOS and EMS to a common chemical agent, namely PAA. Both PAP and PAA are metabolized further to the p-hydroxylated forms, FIPAP and FIPAA (Figure 7). Such compounds readily autoxi-dize to the benzoquinoneimine, which is reactive toward nucleophiles such as the sulfhydryl and amino moieties present on many biological molecules. Thus, upon oxidization, FIPAA and FIPAP may react with macromolecules as a hapten to form immunogenic targets. HPAA possesses some chemical properties... 

If a hapten does not contain free carboxyl, such group(s) may often be introduced. Alkylation of oxygen or nitrogen substituents with halo-esters, followed by hydrolysis of the ester, is frequently used for this purpose (Kabakoff, 1980). For steroids, carboxyl groups may be introduced to the hydroxyl or keton groups, through the formation of hemisuccinate esters or (carboxymethyl)oximes, respectively. 

Fig. 8.5 Molecular recognition of haptens by engineered lipocalins versus antibodies. (Top) Crystal structure of the anticalin DigAl 6 with the bound digoxigenin (yellow). The arrow points to the hydroxyl substituent of steroid ring A, which had served for covalent attachment - via a flexible spacer - to a solid support during the selection process for this BBP variant. The Cq positions of the 16 initially ran-...

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