Selectivity in the modification of the alpha-amino groups of hemoglobin on reductive alkylation with aliphatic carbonyl compounds. Influence of derivatization on the polymerization of hemoglobin S.
The reactivity of the alpha-amino groups of the alpha- and beta-chains of hemoglobn toward reductive alkylation using limiting concentrations of the aliphatic carbonyl compounds, acetaldehyde (ethylation), glyoxylic acid (carboxymethylation), glycolaldehyde (hydroxyethylation), glyceraldehyde (dihydroxypropylation), and dihydroxyacetone (dihydroxyisopropylation) has been investigated. Hemoglobin A reductively ethylated at the alpha-amino groups eluted on CM-52 ahead of unmodified hemoglobin A, and hemoglobin A reductively ethylated at the epsilon-amino groups. This observation is similar to that seen on hydroxyethylation and dihydroxypropylation of the alpha-amino group of hemoglobin A. The presence of the alpha-hydroxyl or the carboxyl group in the carbonyl component used in the reductive alkylation influences considerably the selectivity pattern during the derivatization. The alpha-amino groups of the alpha- and beta-chains are modified to nearly the same degree during reductive hydroxyethylation as well as during reductive dihydroxypropylation. Reductive ethylation (aldehyde lacking the alpha-hydroxyl group) exhibited a slight preferential reaction at Val-1(beta). The presence of a negatively charged carboxyl group in the carbonyl component, i.e. glyoxylic acid, made this preferential reaction at Val-1(beta) even more pronounced. When the reductive alkylation is carried out with dihydroxyacetone (a ketone instead of an aldehyde), the dihydroxyisopropylation occurred at a slower rate and exclusively at Val-1(beta). The ethylation, hydroxyethylation, carboxymethylation, and dihydroxypropylation of the alpha-amino groups of hemoglobin S increased its solubility from the value of 16 g/dl for the unmodified protein to about 25 g/dl for the modified protein. Thus, the alkyl chains on the alpha-amino groups on the polymerization have a strong inhibitory influence. In order to determine the influence of the alkyl chains at the alpha-amino groups of alpha- and beta-chains on polymerization, hybrid hemoglobin S tetramers with hydroxyethylation either at Val-1(alpha) or at Val-1(beta) have been prepared. The solubility of each hybrid is about 26 g/dl. Thus, the hydroxyethyl group either on the alpha- or the beta-chain appears to interfere with the polymerization of deoxygenated HbS to the same degree. The inhibitory influence of the hydroxyethyl chain at Val-1(alpha) on the polymerization, compared with the lack of such an influence when this alpha-amino group is modified by cyanate, suggests that a carbamoyl group on Val-1(alpha) can be accommodated in the intermolecular contact region involving this segment of the molecule without seriously perturbing the mo
D000478:Alkylation; D055598:Chemical Phenomena; D002621:Chemistry; D006441:Hemoglobin A; D006451:Hemoglobin, Sickle; D006801:Humans; D010084:Oxidation-Reduction; D011108:Polymers; D011487:Protein Conformation
D006451:Hemoglobin, Sickle; D011108:Polymers; D006441:Hemoglobin A