Stabilization of the maturation promoting factor (MPF) from Xenopus laevis oocytes. Protection against calcium ions

Maturation promoting factor (MPF) activity was recovered from progesterone-matured Xenopus oocytes cytosol, fractionated by polyethylene glycol-20,000 or ethanolic precipitation. An improved stabilization of the biological activity was obtained by adding adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S) (50 microM) to the preparation buffers. Neither Ca2+ ions nor calmodulin inhibit the partially purified MPF.