Endogenous heterogeneity of relaxin and sequence of the major form in pregnant sow ovaries.

Using an extraction procedure that minimized proteolysis, followed by gel filtration, cation-exchange FPLC, and reverse-phase HPLC, the present study unambiguously showed the presence of multiple isoforms of relaxin in the ovaries of pregnant sows. Four relaxin isoforms were isolated (designated as R-I1, R-I2, R-II1 and R-III1). They had a similar migration pattern on SDS/urea PAGE, and showed no significant difference in biological activity. HPLC separation of the reduced and S-pyridylethylated relaxin variants indicated that R-I1, R-I2 and R-III1 each contained multiple relaxin molecules which showed variability of the B-chain, whereas R-II1 contained mostly a single relaxin molecule with only slight B-chain variability. R-II1 was thus considered likely to be the major form of relaxin stored in the ovary. Sequence analysis revealed that R-II1 contained 22 amino-acid residues in the A-chain and 29 residues in the B-chain, with a total molecular mass of 5814.8 Da. It was thus equivalent to CM-a' relaxin designated by Sherwood and O'Byrne (1974).