Characterization of the High Molecular Weight Form of Epidermal Growth Factor

Abstract In crude homogenates of the submaxillary gland of the male mouse, epidermal growth factor activity is found almost entirely in a high molecular weight complex. The complex has a molecular weight of about 74,000 and appears to be composed of 2 molecules of epidermal growth factor (6,045 molecular weight) and 2 molecules of a binding protein (29,300 molecular weight). The complex is stable only in the range of pH 5.0 to 8.0, and its behavior during isoelectric focusing, gel filtration, and ultracentrifugation suggests that it may be in a slow equilibrium with its subunits. In addition, the complex appears to undergo a concentration-dependent aggregation. The biological activity of the high molecular weight complex is proportional to its fractional content of the low molecular weight factor. No evidence was found which indicated that the binding protein might affect the biological activity of the low molecular weight epidermal growth factor. It is postulated that the high molecular weight form of epidermal growth factor is an enzyme-product complex. The substrate is presumed to be the epidermal growth factor precursor which is recognized by a specific arginine esterase, the binding protein.