Abstract
Extract: A 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 SO4 precipitation, gel nitration, and preparative poly-acrylamide gel electrophoresis. This protein has a molecular weight of 12,000. It contains large numbers of serine, glycine, and glutamic acid residues, 0.85% 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.
Speculation: Aggregation and precipitation of CaPP in saliva of patients with CF seems to be induced primarily by elevated levels of calcium in saliva. This precipitation may be entirely, or in part, responsible for focal obstruction of submaxillary gland ducts in patients with CF. However, little or no CaPP is secreted in the lower gastrointestinal or tracheobronchial tracts. Therefore, CaPP does not play a more general role in the obstructive processes which characterize CF.
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Boat, T., Wiesman, U. & Pallavicini, J. Purification and Properties of the Calcium-precipitable Protein in Submaxillary Saliva of Normal and Cystic Fibrosis Subjects. Pediatr Res 8, 531–539 (1974). https://doi.org/10.1203/00006450-197405000-00001
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DOI: https://doi.org/10.1203/00006450-197405000-00001