Effect of buffers and electrolytes on the stability of uterine progesterone receptors

Abstract

We have investigated the effects of buffers and electrolytes on the stability of the 7S progesterone-receptor complex of guinea pig and rabbit uterine cytosol. Receptor half-life was greater in 5 m m phosphate than in the cationic or zwitterionic buffers tested. The best medium contained 5 m m phosphate, 10% glycerol, and 10 m m monothioglycerol, and was degassed under vacuum. Exposure to 100 m m sodium phosphate, like exposure to 300 m m KCl, resulted in the disappearance of the 7S progesterone binding component and a concurrent increase in binding to a 4 to 5S component. However, Scatchard analyses suggest that 300 m m KCl led to a reduction in the apparent association constant, whereas the “ K a” observed in 5m m phosphate was maintained in 100 m m phosphate.