FLUORESCENT PEPTIDE-HORMONES - DEVELOPMENT OF HIGH-AFFINITY VASOPRESSIN ANALOGS

Highly potent and specific peptide hormone analogues with fluorescent reporter groups are current research goals. Until now, however, only m oderately potent analogues have been described. We report here several types of vasopressin (VP) analogues with different fluorophores attac hed to the peptide. In a first series, fluorophores were attached to t he free epsilon-amino function of [des-amino1-lysine8]VP (dLVP), produ cing agonistic analogues. In a second series, reporter groups were add ed to the N-terminal of open-chain antagonist structures. The biologic al activities of these analogues were assessed by two different sets o f experiments: 1) The measurement of their binding affinities towards the V1a-vasopressin receptor subtype from WRK1 cells or rat liver memb rane preparations; 2) Their ability to stimulate the phospholipase C a ctivity in WRK1 cells. As expected, a simple acylation of fluorophores to dLVP resulted in a considerable loss of affinity. If, however, the Lys8 side chain was extended through double Schiff-base formation wit h glutaraldehyde-ethylenediamine followed by reduction to an aminoalky l aminoalkylamine, single fluorophores could be added without loss of affinity compared to VP. The open-chain analogues, on the other hand, while displaying weak affinity, nevertheless exhibited pure antagonist ic behavior.