The α and γ subunits of 7S nerve growth factor are present in excess concentrations in the mouse submandibular gland

Summary

The 7S nerve growth factor molecule, found in the mouse submandibular gland, is comprised of three distinct protein subunits named α, γ and β-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 α and γ subunits, more than enough to bind all of the β-NGF in the gland to form 7S-NGF. The radioimmunoassay data was confirmed by gel filtration experiments. In the gel filtration experiments, the excess α and γ 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 α and γ subunits was substantiated by ion exchange chromatography, isoelectric focusing polyacrylamide gels and immunoblotting experiments. In conclusion, there are considerable quantities of α and γ subunits present in the submandibular gland which are not bound to β-NGE The functional significance of these excess concentrations of the α and γ subunits is not known.