FLUORESCENCE STUDY OF NEUROHYPOPHYSEAL HORMONES AND THEIR ANALOGS - DISTANCE DISTRIBUTIONS IN A SERIES OF ARGININE-VASOPRESSIN ANALOGS

Analogues of arginine-vasopressin (AVP) in which substitution of the p roline residue in position 7 (by either sarcosine or N-methylalanine) combined with replacement of the cysteine residue in position 1 were t he subject of a fluorescence and molecular mechanics study. We obtaine d two groups of analogues: selective antidiuretic agonists (cysteine o r beta-mercaptopropionic acid in position 1) and presser and uterotoni c antagonists (deamino-penicillamine or -mercapto-beta,beta-cyclopenta methylene-priopionic acid in position 1). Using frequency-domain measu rements of fluorescence resonance energy transfer (FRET) we estimated the distance distribution between the phenolic ring of Tyr(2) and the disulphide bridge Cys(1)-Cys(6). We also analyzed acrylamide quenching of tyrosyl fluorescence to determine the exposure of the tyrosyl ring to the solvent. Results from fluorescence experiments were compared w ith those from Monte Carlo simulation (ECEPP/3 force-field).