Magnetic resonance study of 13C reductively methylated glycophorin and glycophorin glycopeptides |
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Authors: | Robert E Hardy Marsha E Daman Anne M Holbrooks Kilian Dill |
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Institution: | Department of Chemistry, Clemson University, Clemson, SC 29631, USA |
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Abstract: | 13C nuclear magnetic resonance (n.m.r.) spectral data for 13C reductively methylated N-terminal tryptic glycopeptides and for 13C reductively methylated N-terminal glyco-octapeptides derived from homozygous glycophorins AM and AN are presented. Their 13C chemical shift data are compared with the previously published 13C n.m.r. data for 13C reductively methylated homozygous glycophorins AM and AN in order to investigate the means of display of the MN blood determinants by these species. The pH dependence of the 13C resonances of leucine of glyco-octapeptide AN and of serine of glyco-octapepti AM indicated that only a slight structural perturbation occurs at the N-terminus when a large portion of the glycoprotein molecule is removed. However, one structural ‘state’ of 13C reductively methylated glycophorin AM is lost when the glyco-octapeptide AM is produced. The 13C resonance of leucine of glycooctapeptide AN titrated with a of 7.7 (Hill coefficient ). The 13C resonance of serine, on the other hand, exhibited an unusual pH dependence, indicating the existence of some possible steric constraints or hydrogen bonding in this molecule. In comparison to the data obtained for 13C-labelled glycooctapeptide AM molecule, the pH dependence of the chemical shift of the 13C resonance of serine of tripeptide tri-L-serine is also presented. Circular dichroism (c.d.) spectra indicated that the reductive methylation technique does not cause a large perturbation of the glycophorin A molecule. |
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Keywords: | Proteins glycophorin A glycopeptides To whom correspondence should be addressed |
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