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Calcium binding to amino acids and small glycine peptides in aqueous solution: Towards peptide design for better calcium bioavailability Ning Tang, and Leif H. Skibsted J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b01534 • Publication Date (Web): 09 May 2016 Downloaded from http://pubs.acs.org on May 9, 2016
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Journal of Agricultural and Food Chemistry
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Calcium Binding to Amino Acids and Small Glycine Peptides in Aqueous Solution: Towards Peptide Design for
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Better Calcium Bioavailability
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Ning Tang and Leif H. Skibsted*
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Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark
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*Corresponding Author:
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Tel: 45-3533 3221; Fax: 45-3528 3344; E-mail:
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1 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
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Abstract
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Deprotonation of amino acids as occurring during transfer from stomach to intestines during food digestion was found by
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comparison of complex formation constants as determined electrochemically for increasing pH to increase calcium binding
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(i) by a factor of around 6 for the neutral amino acids; (ii) by a factor of around 4 for anions of the acidic amino acids
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aspartic and glutamic acid; and (iii) by a factor of around 5.5 for basic amino acids. Optimized structures of the 1:1
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complexes and ∆Hbinding for calcium binding as calculated by Density Functional Theory (DFT) confirmed in all complexes
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a stronger calcium binding and shorter calcium oxygen bond length in the deprotonated form. In addition, the stronger
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calcium binding was also accompanied by a binding site shift from carboxylate binding to chelation by α-amino group and
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carboxylate oxygen for leucine, aspartate, glutamate, alanine and asparagine. For binary amino acid mixtures, calcium
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binding constant was close to the predicted geometric mean of the individual amino acid binding constants indicating
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separate binding of calcium to two amino acids when present together in solution. At high pH, corresponding to conditions
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for calcium absorption, the binding affinity increased along the series: Lys < Arg < Cys < Gln < Gly ~ Ala < Asn < His