Proteins reactive groups

Anthraquinone dyes have anthraquinone as their base and the carbonyl group (>C=0) as the chromophore. Anthraquinone itself is not a contact allergen. In fact, the anthraquinone ACD dyes have no obvious protein reactive group or substructure for reaction... 

The third route follows the grafting-through approach in which various protein reactive groups are incorporated within a growing polymer chain by using monomers that can react either directly or after polymerization via the introduced reactive moieties with peptides or proteins [69], Noteworthy, this third approach does not necessarily result only in conjugation of one protein/peptide to a polymer chain, but also in conjugation of several protein/peptide to a polymer chain. 

A further complication of these reactions is that many nonhemoglobin proteins contain reactive groups and may also be modified to produce new, potentially toxic, contaminants. It has been difficult to produce a pure modified hemoglobin for toxicity studies because most processes start with relatively cmde stroma-free hemoglobin. 

Long loop regions are often flexible and can frequently adopt several different conformations, making them "invisible" in x-ray structure determinations and undetermined in NMR studies. Such loops are frequently involved in the function of the protein and can switch from an "open" conformation, which allows access to the active site, to a "closed" conformation, which shields reactive groups in the active site from water. 

Dinitrofluorobenzene (86, X = F) is, because of its reactivity, much used for tagging the NH2 group of terminal amino-acids in protein end group analysis. Once it has reacted with the NH2 it is very difficult to remove again and will thus withstand the subsequent hydrolysis of the protein to its constituent amino-acids. 

Activity-based protein profiling (ABPP) is a chemical proteomic strategy in which active-site-directed covalent probes are used to profile the functional states of enzymes in complex proteomes. Activity-based probes (ABPs) can distinguish active enzymes from their inactive zymogens or inhibitor-bound forms. They contain a reactive group intended to modify enzyme active sites covalently and a reporter group (typically rhodamine or biotin) that assists in detection and identification of protein targets. 

The pairs of dyes more commonly used to generate FRET have been extensively reviewed [86-88] and their conjugation to different types of molecules has been facilitated by the incorporation of a range of reactive groups. Some examples are activated esters and iso thiocyanates for reaction with amino groups of proteins or peptides,... 

One might expect that dehydration of a methylol-aducted protein would lead to the formation of Schiff bases, which might be expected to serve as highly reactive groups capable of undergoing further reactions—particularly cross-linking reactions, as the water content of the surrounding solution is reduced. As yet, however, there is little direct evidence that such intermediates are... 

Figure 19.1 A schematic view of the common formaldehyde-induced modifications in proteins. Reactive methylol adducts are formed in the initial reaction between formaldehyde and cysteine or the amino groups of basic amino acid residues. The methylol adduct can subsequently undergo a dehydration reaction to form a Schiff s base. Adducted residues can undergo a second reaction to form methylene bridges or can convert to the ethoxymethyl adduct after the ethanol dehydration step.

At present, the most frequently used methods for PEGylation are chemical conjugation between reactive groups in the drug, such as the primary amine of lysine in protein, and end-reactive PEG derivatives, such as the A-hydroxysuccinimide-... 

This same type of modification strategy also can be used to create highly reactive groups from functionalities of rather low reactivity. For instance, carbohydrate chains on glycoproteins can be modified with sodium periodate to transform their rather unreactive hydroxyl groups into highly reactive aldehydes. Similarly, cystine or disulfide residues in proteins can be selectively reduced to form active sulfhydryls, or 5 -phosphate groups of DNA can be transformed to yield modifiable amines. 

The relative reactivity of a-haloacetates toward protein functional groups is sulfhydryl > imidazolyl > thioether > amine. Among halo derivatives the relative reactivity is I > Br > Cl > F, with fluorine being almost unreactive. The oc-haloacetamides have the same trend of relative reactivities, but will create a terminal amide group not a terminal carboxylate. 

Figure 2.5 The cisplatin reactive group can covalently couple to methionine-, cysteine-, and histidine-containing peptides or proteins. It also reacts with guanine groups to form a covalent modification on the N7 nitrogen.

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