STUDIES ON THE SOLUTION CONFORMATIONS OF NEUROHYPOPHYSEAL HORMONES: COMPARATIVE STUDIES OF [8-D-ARGININE]VASOPRESSIN AND [8-L-ARGININE]VASOPRESSIN IN D2O BY 1 H NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

[8-D-Arginine]vasopressin (DAVP), an active synthetic analog of the naturally occurring neurohypophyseal hormone [8-L-arginine]vasopressin (AVP), was studied in D 2 O at pD 3.3 and 23°C by 1 H nuclear magnetic resonance (NMR) spectroscopy, and chemical shifts (δs) and some of the coupling constants for the nonlabile protons (the protons that do not readily exchange for deuterons in the solvent) were determined and compared to those previously reported by us for AVP in D 2 O at pD 3.8 and 20°C ( Wyssbrod et al., 1979a , b ). Values of δ of corresponding protons in DAVP and AVP are quite similar, and small perturbations in these values for protons in the prolyl-7 and glycyl-9 residues in going from AVP to DAVP can be ascribed to the change in chirality (handedness) at the C α of the adjacent arginyl-8 residue. That the observed perturbations are relatively small (⩽ 0.03 ppm) is probably related to extensive conformational interconversion (averaging) in residues 7-9, which comprise the tail moiety, in both peptides. The conformational states of residues 1-6, which comprise the ring moiety, appear to be, for all practical purposes, identical in both peptides.