Proton magnetic resonance comparison of neurohypophyseal hormones and analogs: deletion of amino groups and the conformation of lysine vasopressin.

Proton nuclear magnetic resonances of two analogs of the mammalian antidiuretic hormone, lysine vasopressin, have been assigned. The analogs studied were deamino-lysine vasopressin and deamino-8-tosyllysine vasopressin, formally derived from lysine vasopressin by removal of the potential cationic sites. Most assignments made in deuterated dimethylsulfoxide at 220 MHz were directly derived from the already determined spectrum of lysine vasopression in this solvent [Walter et al., Proc. Nat. Acad. Sci. USA (1972) 69, 1920]. Comparison of chemical shifts of peptide NH peaks, alphaCH-NH coupling constants, temperature dependence of peptide NH resonances, and proton-deuterium exchange rates revealed that from a conformational standpoint both deamino analogs occupy intermediary positions between lysine vasopressin and oxytocin.