Progesterone-binding components of chick oviduct: partial purification and characterization of a calcium-activated protease which hydrolyzes the progesterone receptor

Abstract

A Ca2+-activated protease was purified from laying hen oviducts. This enzyme can catalyze the limited proteolysis of the native chick oviduct progesterone receptor subunits, A and B, to smaller hormone-binding fragments. The protocol used has resulted in a 2000-fold purification of the enzyme in 40% yield from hen oviduct postmitochondrial supernatant fractions. This resulted in an active, purified protease preparation which can be used as an analytical tool for studying receptor protein structure. Characterization of the purified enzyme showed that it is activated by Ca2+ (0.5-1 mM), has a MW of 113,000 and a sedimentation value of 6 S. No effect of calmodulin (Ca2+-dependent regulator) could be shown on the enzymatic activity of the protease. The enzyme has a Km of 1.04 .times. 10-8 M for the receptor protein substrate. The protease is inactivated by sulfhydryl attacking reagents and thus can be classified as a sulfhydryl protease. This protease exhibits remarkable similarities to the receptor transforming factor (RTF), a Ca2+-activated protease which performs a limited proteolysis on the calf uterine estrogen receptor.