Adenylate cyclase enhancing factor from rat osteosarcoma cytosol

A cytosol factor from a transplantable rat osteosarcoma stimulates the adenylate cyclase (ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1) activity of partially purified membranes 1.5 fold at pH 7.6 and over 5 fold at pH 6.5. This effect can also be seen at maximum Gpp(NH) stimulation of the enzyme. The cytosol factor is non-dialyzable, ultrafiltrable through a 100,000 dalton exclusion membrane, heat labile and trypsin digestible. The stimulation is immediate, is independent of Ca²⁺, exhibits sygmoidal concentration dependency and is enhanced by GTP. The factor did not bind GTP. The stimulatory activity was fully recovered in two Sephadex G-100 fractions of approximate molecular weights of 55,000 and 29,500. Unlike the starting material the fractions were not stable to freeze-thawing or lyophilization. A similar factor could not be found in embryonic bone, nor did the osteosarcoma factor affect bone adenylate cyclase.