Reactivity of Glu-22(beta) of hemoglobin S for amidation with glucosamine.
Reactivity of Glu-22(beta) of hemoglobin S for amidation with glucosamine.
复制标题
血红蛋白 S 的 Glu-22(β) 与葡萄糖胺酰胺化的反应性。
DOI：
10.1021/bi00339a024
复制
发表时间：
1985
期刊：
影响因子：
2.9
通讯作者：
Seetharam,R
中科院分区：
文献类型：
--
作者：
Acharya,AS;Seetharam,R
X-ray diffraction analysis of deoxyhemoglobin S crystals has implicated that a number of carboxyl groups of the protein are present at or near the intermolecular contact regions. The reactivity of these or other carboxyl groups of hemoglobin S for the amidationwith an amino sugar, ie, glucosamine, and the influence of amidation on the oxygen affinity and polymerization have been investigated. Reaction of oxyhemoglobin S at pH 6.0 and 23 C with 20 mM 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide (EDC) and 100 mM [3H] glucosamine for 1 h resulted in an incorporation of nearly two residues of glucosamine per tetramer. The amidation was very specific for the carboxyl groups of globin; the glucosamine was not incorporated into theheme carboxyls. Derivatization of hemoglobin S by glucosamine increased the 02 affinity of the protein but had no influence on either the Hill coefficient or the Bohr effect. Amidation by glucosamine also increased the solubility of deoxyhemoglobin S by about 55%. Tryptic peptide mapping of the modified hemoglobin S indicated that the peptides/3-T3 and jS-T5 contained the glucosamine in-corporated into the protein. Sequence analysis of glucosamine-modified 0-T3 and j8-T5 demonstrated that the-carboxyl groups of Glu-22 and Glu-43, respectively, had been derivatized with glucosamine. The residue Glu-43 (/3) shows a high selectivity toward glycine ethyl ester also, whereas Glu-22 (/3) is not reactive toward this amine. The results demonstrate that the selectivity of amidation by glucosamine is distinct from that of glycine ethyl ester and is apparently related to the differences in propensity of the carbodiimideactivated-carboxyl groups of Glu-22 (/3) and Glu-43 (ß) toundergo aminolysis with these two amines. e presence of valine at the sixth position in the| 3-chain of hemoglobin S (HbS) 1 (Ingram, 1956), as opposed to the glutamic acid in that of HbA, is responsible for the polymerization of the protein in its deoxy conformation [reviewed by Dean & Schechter (1978a-c)]. Analysis of the deoxy-HbS crystals has shown that the basic unit of the deoxy-HbS polymer is a double-stranded fiber: each strand is formed of tetrameric protein molecules. In these double-stranded fibers, the Val-6 (/3) of one HbS molecule interacts with the hydrophobic side chains lying between the E and F helices of the ß-chain of an adjacent tetramer (Wishner et al., 1975; Love et al., 1978, 1979). Besides the primary site of interaction involving the Val-6 (/3), a number of other noncovalent intermolecular interactions involving specific functional groups of the protein (quinary interactions; Edelstein, 1980) have been suggested to contribute in a cooperative way to the polymerization process as well as to the stability of the polymerized gel. Analysis of the deoxy-HbS crystals has indicated that the carboxyl groups of Glu-22 (/3), Asp-73 (0), Glu-121 (/3), and
