Studies on molecular weights of two peptide hormones from the urophysis of white sucker (Catostomus commersoni).

The molecular weights of two active principles extracted from the urophysis of the teleost fish Catostomus commersoni in 0.1 N HC1 or in 0.25% acetic acid have been investigated by gel filtration chromatography and SDS-polyacrylamide gel electrophoresis. Two peptides with urotensin I Tlong-acting rat hypotensive) activity and two peptides with urotensin II (fish smooth muscle stimulating) activity were found by these procedures. The smaller of the two urotensin I peptides (molecular weight 1200-1700), designated urotensin Is, was shown to be a fragment of the larger peptide (molecular weight 2300-3000) which is produced by acid hydrolysis withour loss of rat hypotensive activity. The two urotensin II peptides are suggested to represent either a monomer and a dimer or open and closed forms of a peptide.