The presence of a heat-stable cytosolic factor in rat submandibular gland which activates Na+,K+-ATPase.

A low molecular weight substance is present in the soluble fraction of the rat submandibular gland which activates Na+,K+-ATPase. Varying amounts of cytosolic protein from rat submandibular gland were added to a heavy microsomal preparation of the same tissue. A dose-dependent activation of the Na+,K+-ATPase was observed, with a peak activation of approximately 82% occurring when 9.0 micrograms/mL of cytosolic protein was included in the assay. The activating factor is heat stable and soluble following heat treatment. The factor elutes at a molecular mass of 600 daltons as determined by molecular sieve column chromatography. Ultraviolet-visible scanning of the elute material results in an absorbance at 210 nm, which is characteristic of a low molecular weight peptide.