Protein relative reactivity

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. 

In contrast to the reactivity of N-sulfonyloxy and N-acetoxy esters of arylamides and arylamines, the relative reactivity of protonated N-hydroxy arylamines with nucleophiles generally decreases in the order DNA > denatured DNA > rRNA = protein > tRNA nucleotides s nucleosides s methionine = GSH (2,13-17,30,36,40,127,129, 130). Furthermore, the rate of reaction with DNA was found to be not only first order with respect to N-hydroxy arylamine concentration, but also first order with respect to DNA concentration (127,129,131). These data suggested that the reaction mechanism was... 

The reactive oxygen species involved with protein oxidation can be generally categorized according to their relative reactivity as follows ... 

The relative reactivity of a-haloacetates toward protein functionalities is sulfhydryl > imid azolyl > thioether > amine. Among halo derivatives the relative reactivity is I > Br > Cl > F, with fluorine being almost unreactive. The a-haloacetamides have the same trend of relative... 

By varying all the parameters of the process the authors prepared a set of copolyesters containing units and blocks with a tertiary amino group, which, in turn, could be transformed into a hydrophilic hydrochloride salt thus imparting water-compatibility to the initially organosoluble macromolecules. The principle involved was the formation of a block-type structure of chains in order to facilitate their further protein-like folding in an aqueous medium. It was shown that the main factors responsible for the blockiness were the relative reactivities of the (B) and (C) components (NMDEA and bisphenol) and the order of their addition to the reaction. 

Table III. The Effects of Different Reagents on the Relative Reactivity of Amino and Sulfhydryl Groups in Proteins...

The relative ease of oxidation of a model disulfide, di-DNP-cystine, is illustrated in Table XIXe, where the amount of oxidant used was just in 50% excess (Ramacbandran, 1961). The yield of 73% DNP-cysteic acid is not far from values for yields of cysteic acid (80-90 %) from performic acid oxidation of cystine (Schram et ah, 1954). Proteins with reactive —SH, —S—S—, or free —NH2 groups therefore pose problems when side reactions in the oxidative cleavage of peptide bonds is to be avoided (cf. Section V, B). 

The iodination of proteins has long been a very popular modification reaction. This reaction, performed under mild conditions, has been applied to such varied ends as the detection of side-chains at the catalytic sites of proteins, investigation of the relative reactivity of tyrosyl side-chains, and the introduction of heavy atoms in connection with X-ray diffraction studies. The availability of two radioactive iodine isotopes, 1 with a half-life of 56 days, and 1 with a half-life of 8 days, has been very extensively exploited in the preparation of hormone derivatives of high specific activity for radioimmunoassay and receptor studies. 

Seven carboxylic acid-bearing drugs (Figure 13) that have been reported to bind covalently to protein, in vitro and in vivo, with different degrees [27-34] of reactivity, were selected to evaluate the technique. The degrees of reactivity of the AG metabolites of these seven drugs were determined based on a reactivity index developed for each drug. It was found that the relative reactivity rank of the AG metabolites of these seven compounds was... 

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