No abstract

ExtractA calcium-precipitable protein (CaPP), previously shown to cause turbidity of submaxillary saliva (SMS) in patients with cystic fibrosis (CF), was purified from normal and CF-SMS by (NH4) 2 S 0 4 precipitation, gel filtration, and preparative polyacrylamide gel electrophoresis. This protein has a molecular weight of 12,000. I t contains large numbers of serine, glycine, and glutamic acid residues, 0.85y0 phosphorus as phosphate monoester, and small amounts of carbohydrate. Precipitation (aggregation) of purified CaPP occurs at basic pH values in the presence of ionic calcium and is enhanced by increasing calcium concentration, CaPP concentration, or pH. Aggregated CaPP binds calcium in molar quantities equal to the number of phosphate prosthetic groups. Alkaline phosphatase removes all phosphate from CaPP and eliminates calcium-induced precipitation. Studies of CaPP from CF saliva have demonstrated no electrophoretic or compositional differences from normal CaPP. Higher than normal pH values or elevated CaPP concentrations are not present in SMS of patients with CF and do not contribute to the formation of turbid SMS.