Examination of noncollagen protein composition of the footplate and superstructure of the otosclerotic stapes.

We have differentially precipitated 2 fractions of noncollagen proteins extracted from separately pooled superstructure and footplate of surgically removed stapes of patients from both sexes, who have suffered from otosclerosis. The two fractions were: EDTA-soluble, CaCl2 precipitable (Fraction-1) and EDTA-soluble, CaCl2 non-precipitable proteins. The protein pattern of these two fractions was compared by isoelectric focusing and two-dimensional gel electrophoresis. The phosphoprotein fraction (Fraction-1) of the otosclerotic stapes footplate contained acidic (pI 3-6), low molecular weight (20-40 kD) proteins, which were not detected in the superstructure and temporal cortical bone. Two-dimensional mapping of the Fraction-2 showed predominantly acidic proteins in the footplate and some basic minor components in the superstructure. The lack of the low molecular weight proteins in the superstructure proves the localisation of the otosclerotic process only in the footplate.