title: Calcium binding to dipeptides of aspartate and glutamate in comparison with orthophosphoserine.
abstract: Aspartate binds calcium(II) better than glutamate with Ka = 7.0 ± 0.9 L mol⁻¹ for Asp and Ka = 3.0 ± 0.8 L mol⁻¹ for Glu, respectively, as determined using calcium-selective electrodes for aqueous solutions of ionic strength 0.20 at 25 °C at pH of relevance for milk products. For the mixed peptides, the affinity seems additive with Ka = 27 ± 3 L mol⁻¹ for Asp-Glu and 22.7 ± 0.1 for Glu-Asp as compared to the expected 21 L mol⁻¹. In contrast, for Asp-Asp, the affinity is less than additive with Ka = 23 ± 5 L mol⁻¹ as compared to the expected 49 L mol⁻¹, whereas for Glu-Glu, the affinity is more than additive with Ka = 26 ± 4 L mol⁻¹ as compared to the expected 9.0 L mol⁻¹, indicating specific structural effects for Glu-Glu. Ionic strength effects, 1.0 versus 0.20 studied, are similar for Asp and Glu with decreasing affinity for higher ionic strength, whereas the dipeptides with Glu as C-terminus are more sensitive to increasing ionic strength than with Asp as C-terminus. Despite little affinity of calcium to serine with Ka = 0.9 ± 0.2 L mol⁻¹, Glu has increasing affinity for calcium in the serine dipeptide Ser-Glu with Ka = 10 ± 3 L mol⁻¹, which becomes comparable to phosphorylated serine with Ka = 22 ± 5 L mol⁻¹.
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Martina
authors.initials: M
authors.lastname: Vavrusova
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D001628:Beverages; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002136:Calcium, Dietary / Q000032:analysis / Q000378:metabolism; D002614:Chelating Agents / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism*; D005503:Food Additives / Q000378:metabolism*; D005527:Food, Fortified; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009753:Nutritive Value
chemical_list: D002136:Calcium, Dietary; D002614:Chelating Agents; D004151:Dipeptides; D005503:Food Additives; C108952:aspartyl-aspartic acid; C021030:gamma-glutamylaspartic acid; C094686:glutamyl-glutamic acid; C038676:aspartylglutamate; D002118:Calcium