A Bovine Low Molecular Weight Bone Morphogenetic Protein (BMP) Fraction

Abstract

A low MW bone morphogenetic protein fraction (BMP) is quantitatively extracted from bovine bone matrix by an inorganic-organic CaCl2-urea solvent mixture and fractionated by ion exchange and gel chromatography. The BMP fraction induces differentiation of perivascular mesenchymal type cells into cartilage and bone inside the mouse's thigh, outside of double walled diffusion chamber, in muscle pouches in the rabbit anterior abdominal wall, and in 0.8 cm trephine defects in the rat's skull. Bovine BMP may consist of electrophoretic components ranging from 12 K to 30 K in MW. The main components correspond to a MW of 23 K, 18 K and 12 K when they are compared with the mobilities of standard proteins. Because it was invariably present in all of the fractions with osteoinductive activity, circumstantial evidence leads to a 17 to 18 K component for a BMP. The possibility of a diameter monomer system for BMP activity also warrants consideration. The polypeptide portion constitutes only about 80% to 85% of the dry weight of the mixture of the three electrophoretic components, and suggests that the BMP fraction contains glycoproteins. Characteristically, glycoproteins migrate anomalously on SDS gels and create doubt about whether the major bands represent true MW. Nevertheless, the data clearly point to the low MW protein fractions for the direction of future work on BMP.