SOLUTION PROPERTIES OF β NERVE GROWTH FACTOR PROTEIN AND SOME OF ITS DERIVATIVES

The molecular weight of β nerve growth factor protein determined by sedimentation equilibrium in sodium acetate buffer, pH 40, and at protein concentrations around 0‐5 mg/ml agrees with the value obtained from the amino acid sequence and confirms the dimeric character of the protein under these conditions. At pH values of 5.0 or greater, β nerve growth factor protein shows either partial dissociation into monomers or aggregation to higher polymers or both phenomena. The extent of dissociation or aggregation depends on buffer type and pH and is most pronounced at alkaline pH. The variation of molecular weight of β nerve growth factor with solvent conditions is similar to that of insulin or proinsulin. Removal of either the two COOH‐terminal arginine residues or the two NH 2 ‐terminal octapeptide sequences from the protein has no effect on its solution properties at acid pH, the protein remaining a dimer. Species such as 2‐5 S nerve growth factor or cyanogen bromide cleaved nerve growth factor which are partically deficient in COOH‐terminal arginine residues and/or NH 2 ‐octapeptide or nonapeptide sequences are also dimers at pH40. The protein derivative which lacks the two NH 2 ‐terminal octapeptide sequence does not, like β‐nerve growth factor, display dissociation or aggregation behavior at neutral pH, indicating that these sequences are involved in monomer‐monomer interactions.