Complex Formation between Bovine Neurophysin-I and Oxytocin, Vasopressin, and Tripeptide Analogs of Their NH2-terminal Region

Abstract

Abstract Complex formation between bovine neurophysin-I and oxytocin, (8-lysine)vasopressin, or tripeptide analogs of the NH2-terminal region of these hormones, Cys(Me)-Phe-Ile-NH2 and Cys(Me)-Tyr-Phe-NH2, has been studied using ultraviolet absorption and circular dichroism difference spectroscopy between 250 nm and 350 nm. The results suggest that upon complex formation residues 2 and 3 of the hormone molecule are bound in a hydrophobic region of neurophysin, while tyrosine-49 of the neurophysin molecule moves from a hydrophobic to a hydrophilic environment. Tyrosyl circular dichroism spectral changes due to complex formation have been compared to the corresponding tyrosyl absorption spectral changes. This comparison shows that the vibronic fine structure in tyrosyl circular dichroism difference spectra may be used to characterize the microenvironment of tyrosyl residues in proteins.