Abstract: The application discloses (A) a growth-promoting polypeptide having molecular weight from about 5,000 to about 7,000 chromatographic mobility under electrophoresis from about 0.25 to about 0.37 relative to lysine at pH 5 and from about 0.17 to about 0.43 relative to aspartic acid at pH 7.5, terminal amino acid at its amino end being asparagine or aspartic acid, and respective amounts of aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, leucine, tyrosine, phenylalanine, lysine, arginine, trypophan, and cysteine or carboxymethyl cysteine, and also a couple of instances also methionine, isoleucine and histidine; and (B) the derivation of the polypeptides from blood serum or plasma or a plasma fraction by combined steps of (a) homogenizing the starting material in water, (b) admixing a solution of hydrochloric acid in ethanol thereby splitting the polypeptide from its carrier proteins and precipitating them, (c) adjusting the pH to 8.

Abstract: Disclosed are in vitro active cell growth factors that stimulate deoxyribonucleic acid synthesis in the cells, are polypeptide in chemical structure, having a molecular weight range of from 4,000 to 6,000 and an isoelectric range of from pH 4.3 to 5.3, are inert to about 72% aqueous ethanol containing by volume about 0.047% of concentrated hydrochloric acid, soluble in and precipitated from such acid aqueous ethanol solution by admixing in it 3.5 times its volume of a mixture of five parts of acetone with three parts of ethanol, and are soluble in about twice their weight of 20% formic acid.