Isolation and amino acid sequence of urotensin II from the sturgeon Acipenser ruthenus.

Urotensin II (UII) peptides have previously been isolated from the urophysis (the neurohemal organ of the caudal neurosecretory system) of several teleost fish, and the UII amino acid sequences have been determined. Chondrostean fish, such as the Acipenseridae (sturgeon), though without a distinct urophysis, also have a caudal neurosecretory system, which has been indicated by bioassay and immunological evidence to contain UII-like peptides. In the present studies, we investigated by UII radioimmunoassay the UII-like peptides in the spinal cord of three Acipenser species, and isolated and sequenced UII from one of them. As expected, much more UII immunoreactivity (UII-IR) was found in caudal than in anterior spinal cord extracts. In addition, caudal extracts from A. ruthenus were found to contain much more UII-IR (whether determined on a UII-IR/weight or UII-IR/fish basis) than those from the larger A. stellatus and A. guldenstadti. UII was therefore isolated from A. ruthenus and its amino acid sequence was shown to be H-Gly-Ser-Thr-Ser-Glu-Cys-Phe-Trp-Lys-Tyr-Cys-Val-OH. This sequence is identical at positions 6-11 (the disulfide ring) with the known teleost UII peptides, and has acidic and hydrophobic amino acids at positions 5 and 12, respectively, as do the teleost UII peptides. Overall sequence identity with the various forms of teleost UII was 58-83%.