Rainbow trout corpuscles of Stannius: stanniocalcin synthesis in vitro.

In fresh-water rainbow trout, Oncorhynchus mykiss (formerly called Salmo gairdneri), experimentally induced mild hypercalcemia results in release of immunoreactive stanniocalcin from the corpuscles of Stannius (CS) and stimulated synthetic and releasing activities of the glands as measured in vitro. Pulse-chase experiments showed that stanniocalcin (STC) is a 56-kDa glycoprotein, processed from a 64-kDa precursor, prostanniocalcin (PSTC). PSTC and STC are homodimeric molecules that are readily split into monomers in the presence of reducing agents such as 2-mercaptoethanol. The monomeric form of PSTC and STC contains an approximately 5- to 6-kDa glycomoiety. Neither this sugar residue nor the NH2-terminal amino acid sequences of PSTC or STC proved to contain antigenic sites for the antiserum used in this study. Two-dimensional gel electrophoresis indicated the presence of several isoforms of PSTC and STC molecules that may reflect different stages of maturation of the (pro)hormone.