Nerve growth factor: biosynthetic products of the mouse salivary glands. Characterization of stable high molecular weight and 32,000-dalton nerve growth factors

Nerve growth factor (NGF) is a protein required for the growth and development of sensory and sympathetic neurons. The NGF is present in high concentrations in male mouse salivary glands, bovine seminal plasma, and snake venom. The physiological significance of NGF in these sources is not known: it might be a part of a high molecular weight (HMW) protein with possibly different biological function and be cleaved to the functional size by proteases. In an attempt to isolate a HMW protein containing as part of its structure the low molecular weight (LMW) NGF (2.5S), mouse salivary glands were homogenized in the presence of either 8 M urea or 6 M guanidine hydrochloride (Gdn X HCl) in order to denature proteases. This procedure revealed that the LMW NGF is a part of two HMW proteins that are biologically and immunologically homologous to the mouse 2.5S NGF. One of these HMW proteins (Mr 32,000 NGF) was purified and shown to be biologically active in the NGF bioassay. Furthermore, this Mr 32,000 NGF was cleaved by the gamma subunit of mouse HMW NGF to the 2.5S NGF. Evidence is also presented that there may be a HMW protein(s) with apparent molecular weights ranging from 94,000 to 200,000 and immunologically homologous to the three subunits (alpha, beta, gamma) of 7S NGF. This HMW NGF is biologically active in the NGF bioassay, and its activity is inhibited by antibody to the beta subunit. Furthermore, in contrast to mouse 7S NGF, this HMW NGF does not dissociate in either 8 M urea or 6 M Gdn X HCl.