Esterification of the propionate groups promotes alpha/beta hemoglobin chain homogeneity of CN-hemin binding |
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Authors: | Jennings Therese M McDonald Melisenda J |
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Institution: | Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854, USA. |
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Abstract: | This study examines the post-translational role of peripheral propionate groups in the incorporation of the Fe-protoporphryin IX heme into nascent alpha- and beta-globin chains. Human apohemoglobin (a heme-free alpha/beta dimer) in 0.05 M potassium phosphate buffer, pH 7, at 20 degrees C was titrated with either CN-protohemin (native heme with two peripheral propionate groups), or CN-dimethylester hemin (a modified heme with two methyl ester groups in place of the propionate groups). Soret spectrophotometric CN-hemin titrations confirmed that a spectral shift resulted upon binding of protohemin, but no spectral shift occurred upon binding the dimethylester derivative. Recent studies have correlated a Soret spectral shift with the preferential heme binding to the alpha subunit of apohemoglobin. The absence of a Soret wavelength shift (in conjunction with molecular modeling) presented here suggested that the modification of heme propionate groups prevented the formation of an alpha-heme/beta-globin intermediate, a requisite step in the normal assembly of functional hemoglobin. |
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Keywords: | Human hemoglobin Fe-protoporphryin IX Heme propionate groups Protoheme dimethyl ester Heme binding Hemoglobin assembly Spectroscopic titrations CN-heme derivative Molecular modeling |
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