Nerve growth factor: subunit interactions in the mouse submaxillary gland 7S complex.

Sedimentation velocity analyses of the isolated subunits of mouse 7S nerve growth factor (NGF) and their binary complexes have been performed. The 2.5S (beta) form of NGF binds 2 alpha subunits independent of the presence of gamma subunits. Two gamma subunits are also complexed by 2.5S NGF; however, this interaction is dependent on the presence of a carboxyl terminal arginine residue on the beta polypeptide chain. The partial loss of this residue in 2.5S NGF preparations results in a ternary complex(es) with a reduced sedimentation coefficient(s). The two binary complexes formed (alpha 2-beta and beta-gamma 2) show markedly different pH stability profiles. The alpha and gamma subunits do not form a demonstrable complex, but apparently can interact in the ternary complex to render it more stable than the sum of the alpha-beta and beta-gamma interactions.