Effects of synthetic peptide fragments of teleocalcin (hypocalcin) on calcium uptake in juvenile rainbow trout (Salmo gairdneri).

A rainbow trout fry bioassay based on 45Ca uptake was used to compare the effects of pure coho salmon teleocalcin (TC) and several synthetic peptide fragments of TC. Calcium uptake in the fry exhibited a cycle, with an amplitude variation of 3.3 to 48.8 mumol.kg-1.hr-1 and a periodicity of 8 to 21 days. The N-terminal 1-20 amino acid peptides of both eel and salmon TC significantly inhibited 45Ca uptake at the high point of the calcium uptake cycle (up to 75%), although the effective doses of the peptides on a molar basis were 20 to 200 times that of the intact molecule. In contrast, the C-terminal fragment of eel TC (amino acids 202-231) did not have an inhibitory effect on calcium uptake. Instead, it significantly enhanced 45Ca uptake in trout fry (up to sixfold) at the low point of the calcium uptake cycle.