Purification and Characterization of Rat Relaxin*

Abstract

Two highly purified forms of relaxin, designated CMl and CM2, were obtained from rat ovaries collected on day 20 of gestation. The isolation procedure consisted of aqueous extraction, followed by fractionation with Sephadex G-50 and ion exchange chromatography. The yields of CMl and CM2 were approximately 140 μg/geq ovarian fresh tissue. No difference in biological potency between CMl and CM2 was found when they were bioassayed with mouse pubic symphysis bioassays. Physicochemical analyses indicated that CMl and CM2 were similar but not identical. The molecular weights of CMl and CM2 were approximately 6000, as determined by ultracentrifugation. Analytical acrylamide disc gel electrophoresis at pH 4.3 demonstrated that CMl and CM2 had different electrophoretic mobilities. Electrofocusing indicated the isoelectric points of CMl and CM2 were pH 7.6 and pH 9.4, respectively. The amino acid compositions of CMl and CM2 were similar but not identical. Slab gel electrophoresis in polyacrylamide gel with sodium odecyl sulfate showed that both reduced rat relaxin and reduced porcine relaxin migrated farther than their unreduced forms. This observation supports the view that rat relaxin, like porcine relaxin, consists of two chains linked by disulfide bonds.