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 ± 0.1for 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 K a = 22 ± 5 L mol-1.
| Original language | English |
|---|---|
| Journal | Journal of Agricultural and Food Chemistry |
| Volume | 61 |
| Issue number | 22 |
| Pages (from-to) | 5380-5384 |
| Number of pages | 5 |
| ISSN | 0021-8561 |
| DOIs | |
| Publication status | Published - 5 Jun 2013 |