Evidence for presence of micelle-like protein globules in human saliva

It is known that recently formed acquired enamel pellicles show a globular structure. We have suggested that these globules may be salivary micelles, related to the casein micelles found in milk. The aim of the present study was to examine whether human whole saliva contains micelle-like globules. Micelle-like spherical globules with a diameter of 100–300 nm were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and these had an amino acid profile similar to the pellicle formed after 2 h. The globules solubilized lipid-soluble dyes and could be collected from whole saliva after acidification to pH 3 with lactic acid by centrifugation at 3000 × g for 10 min. Milk micelles could be obtained by a similar procedure. Micelles of this kind have a large surface area and a high density of negative charges on the surface. The presence of micelles in saliva and on the enamel could affect the calcium equilibrium in saliva and thus be of physiological significance.