One-step processing of the amphibian vasotocin precursor: structure of a frog (Rana esculenta) "big" neurophysin.

Vasotocin-associated neurophysin (MSEL-neurophysin) from the frog Rana esculenta has been isolated and sequenced through tryptic and staphylococcal proteinase peptides and cyanogen bromide fragments. This protein appears homologous to the mammalian vasopressin-associated neurophysin with a C-terminal glycopeptide extension homologous to the mammalian copeptin. In contrast to the two-step processing of mammalian vasopressin/MSEL-neurophysin/copeptin precursor, a single cleavage is therefore involved in the processing of the amphibian vasotocin/neurophysin precursor. It appears that the physiological release of the vasopressin-like hormone from the N-terminal end of the protein precursor is not dependent upon a previous trimming of the C-terminal copeptin-like moiety.