The alpha and gamma subunits of 7S nerve growth factor are present in excess concentrations in the mouse submandibular gland.

The 7S nerve growth factor molecule, found in the mouse submandibular gland, is comprised of three distinct protein subunits named alpha, gamma and beta-NGF. In this paper, radioimmunoassays specific for each subunit were used to measure the concentrations of these subunits in homogenates of mouse submandibular gland. It was determined that there were excess concentrations of both the alpha and gamma subunits, more than enough to bind all of the beta-NGF in the gland to form 7S-NGF. The radioimmunoassay data was confirmed by gel filtration experiments. In the gel filtration experiments, the excess alpha and gamma subunits eluted at positions which would indicate that these excess subunits were free and not bound in the 7S-NGF complex. The identity of the excess alpha and gamma subunits was substantiated by ion exchange chromatography, isoelectric focusing polyacrylamide gels and immunoblotting experiments. In conclusion, there are considerable quantities of alpha and gamma subunits present in the submandibular gland which are not bound to beta-NGF. The functional significance of these excess concentrations of the alpha and gamma subunits is not known.