Purification, characterization, and bioassay of teleocalcin, a glycoprotein from salmon corpuscles of Stannius

Abstract

This report describes the isolation of teleocalcin, a glycoprotein hormone from the corpuscles of Stannius (CS) of sockeye salmon (Oncorhynchus nerka), using affinity, gel exclusion, and ion exchange chromatography. In discontinuous, gradient (10-20%) SDS gels under nonreducing conditions, teleocalcin had an estimated molecular weight of of 39,300 and migrated as a single band. Two bands with estimated molecular weights of 28,000 and 32,000 were obtained upon reduction and carboxymethylation of the molecule. In acid-urea gels, teleocalcin migrated as one band with an Rf of 0.17. Amino acid sequence analysis revealed single residues for the first 19 amino acids, with phenylalanine as the N-terminal residue. Teleocalcin did not resemble parathyroid hormone (PTH) with respect to amino acid composition and exhibited no cross-reactivity in two PTH radioimmunoassays. Gas-liquid chromatographic analysis of teleocalcin demonstrated that mannose was the principal sugar present (1.86%) and glucosamine was the only hexosamine identified (2.49%). Smaller quantities of galactose (0.49%), fucose (0.44%), and sialic acid (1.6%) were also found. In bioassays using juvenile rainbow trout (Salmo gairdneri), teleocalcin significantly reduced the rate of net branchial 45Ca uptake at dosages as low as 0.02 microgram/g body wt. This inhibitory effect was dependent upon the branchial calcium uptake cycle that has been identified in this species. Pronounced inhibition was observed during periods of high uptake whereas little or no effect was obtained during the low uptake phase. The results are discussed in relation to a possible role of teleocalcin in regulating this cycle.