The purification of nerve growth factor from bovine seminal plasma. Biochemical characterization and partial amino acid sequence.

Nerve growth factor (NGF), a protein regulating the development and function of certain neural crest derivatives, has been purified from bovine seminal plasma, and extremely rich source of the protein. Around 10 mg of pure NGF (yield, 10-20%) can be isolated from 10 g of lyophilized seminal plasma (around 100 ml of semen). The behavior during purification indicates that, like the NGF in the mouse submandibular gland, bovine NGF exists as a high molecular weight complex that dissociates at extremes of pH to reveal a smaller subunit having NGF biological activity. The isolated low molecular weight form of bovine NGF is a dimer of noncovalently linked polypeptide chains (Mr approximately 15,000 on sodium dodecyl sulfate-polyacrylamide gels), with an isoelectric point of 9.5-10. These properties differ from those of low molecular weight (beta-subunit) mouse NGF, which comprises two noncovalently linked peptide chains of Mr = 13,256 (from sequence studies), and which has an isoelectric point of 9.3. The amino acid sequence of the NH2-terminal 26 residues of bovine NGF has been determined and found to be similar to, but not identical with, that of mouse NGF. Thus, residues 3, 9, and 18, which are threonine, methionine, and valine, respectively, in mouse NGF, are serine, arginine, and isoleucine in bovine NGF.