Interactions of Bovine Neurophysin II with Oxytocin and [8-Lysine] Vasopressin

Evidence from hydrogen-1 and carbon-13 nuclear magnetic resonance studies that the dissociation rate of oxytocin from bovine neurophysin at neutral pH is slow

“…The aromatic tyrosyl protons of oxytocin in the presence of varying amounts of NPII are shown in Figure la. There is an increase in the line width observed as more NPII is added, in agreement with the previous observation at Alazard et al (1974). The NMR spectra of the tyrosyl aromatic protons of [ 1 -hemi-D-[a,/?,/3-2H3]cystine]oxytocin in the presence of varying amounts of NPII are shown in Figure 1 b.…”

“…To complement our l3C NMR studies of the interactions of oxytocin and AVP labeled on the a carbon of the Tyr-2 residue with neurophysins, we have reinvestigated the question of the observed exchange rates for the aromatic protons on this residue. This additional study was necessary, since one group of investigators (Alazard et al, 1974) found a condition of fast exchange for both oxytocin and LVP, while another group (Balaram et al, 1973) found slow exchange (only LVP was studied).…”

“…For the l3C work, sample preparation and acquisition of data were performed as in our earlier work . The studies were done as closely as possible to the conditions of Alazard et al (1974). NP II was dissolved in D2G, 0.1 N NaCl, "pD" (direct meter reading) 6.7 to a concentration of 60 mg/mL.…”

“…From studies with both nonapeptide and tripeptide analogues and derivatives of oxytocin, Breslow and co-workers (Breslow, 1974; Breslow et al, 1971Breslow et al, , 1973 found evidence that the three N-terminal residues of the hormones, y2-Cys-l, Tyr-2, and Ile-3 (Phe-3 in AVP and LVP), are critical for binding. Significant support for this hypothesis has come from various laboratories employing nuclear magnetic resonance (NMR) techniques (Glasel et al, 1973;Hruby et al, 1977b;Griffin et al, 1977;Alazard et al, 1974;Balaram et al, 1973).…”

“…Two proton NMR studies, both involving an observation of the aromatic protons of the tyrosine-2 residue of oxytocin (or LVP) and both done near neutral pH and under very similar conditions of protein concentration with large excesses of hormone, came to opposite conclusions about the exchange rate, with one study (Alazard et al, 1974) finding a fast-exchange condition with a rate »60 s-1, and the other study (Balaram et al, 1973) finding slow exchange and a rate «125 s-1. A deuterium NMR study conducted under quite different conditions at pH 2.5 found a rate >1000 s-1 (Glasel et al, 1973).…”