Noncollagenous proteins of newborn rat calvaria: the possible mineral and collagen binding proteins

Abstract

In order to separate only the mineral and collagen binding (MCB) proteins from the mineral compartment of newborn rat calvaria after the mineral unassociated proteins were removed by washing in 4 M guanidine solution, the sequential extractions were carried out by homogenizing in acetic acid and several neutral solutions with a different ion concentration.Three noncollagenous proteins were solubilized as MCB proteins by sequential extractions and each had an affinity for calcium ions. One is the sialoprotein which has an apparent molecular weight (Mr=) of 80,000–115,000 and stains blue with Stains-all but does not stain with Coomassie blue (CBB), this sialoprotein is expected to bind more tightly to the matrix by ionic bonds than the other two proteins. The protein species of Mr=66,000 is a phosphorylated glycoprotein which contains a small amount of sialic acid and appears to bind to the matrix. Partial amino acid sequence analysis suggests that this protein is osteopontin reported by Oldberg et al (Proc. Natl. Acad. Sci. USA. 83, 8819–8823, 1986).The other Mr=49,000 species may have an affinity for the matrix, although part of this protein binds only to the mineral, and by N-terminal amino acid sequence analysis is found to be derived from serum and the analogue of humanα 2HS glycoprotein.