Study of calcium binding to different preparations of yeast (Saccharomyces cerevisiae) protein by using an ion selective electrode

The calcium binding capacity of a native brewer’s yeast protein (PL) was compared to protein from the same source, after treatment with 3% sodium trimetaphosphate (PLP). Calcium titration was done by the use of an ion-selective electrode. For measurements made at pH 6.5, the number of calcium binding sites per 105g protein was 29 for PL and 37 for PLP. The association constant K was 3.2×10−3 and 2.7×10−3 for PL and PLP, respectively. Dialysis of sample PLP against 0.01 M EDTA increased the number of binding sites to 49. The higher number of binding sites in PLP is explained by the presence of phosphate moieties associated with the protein molecules and also by possible conformational changes occurring in the protein molecules as a result of STMP treatment, exposing a larger number of amino acid side chains capable of combining with Ca2+.©