Effects of molecular structure on the calcium-binding properties of phosphopeptides

Six synthetic phosphopeptides (SPP) and casein phosphopeptides (CPP) were obtained to investigate the relationship between the molecular structure of phosphopeptides and their calcium-binding property. SPP1, SPP2, SPP3, SPP4, SPP5, and SPP6 were synthesized with 0-3 continuous or discontinuous phosphorylated serines based on a core structure of casein phosphopeptides, respectively. CPP were acquired by pancreatin hydrolysis of casein and subsequent purification. The ranking of calcium-binding ability of the six synthetic phosphopeptides was SPP5 > SPP6 > SPP4 > SPP3 > SPP1 ~ SPP2. SPP4 was found to release calcium more easily in a simulated intestinal environment. CPP, contained various fragments ranged from 1 to 4 Ser(P)s, bound calcium slightly weaker than SPP6 that contained same amount of phosphorus with the CPP solution. The number and the position of phosphoserine residue are important factors for calcium-binding activities. SPP4, the phosphopeptide with two discontinuous phosphorylated serines, has the best calcium adsorption efficiency in a simulated intestinal environment among all the tested phosphopeptides.