The kinetics of the precipitation of chemically modified alpha S1-casein by calcium.

The aggregation of alpha S1-casein by Ca is viewed as resulting from a reduction in the net negative charge by the binding of positively charged Ca2+. This reduction in charge leads to the equivalent of isoelectric precipitation. A quantitative relationship between the rate of aggregation of the casein and the monomer net charge is predicted in this isoelectric precipitation model. Precipitation results are presented for alpha S1-casein labelled with dansyl chloride. Providing the changes in charge brought about by the modification are taken into account, the precipitation behaviour of these caseins can be reconciled with that of native alpha S1-casein. This emphasises the role of electrostatic repulsion in this process and lend further support to the isoelectric precipitation model.