The interaction between bovine neurophysins I and II and oxytocin and vasopressin was measured using temperature-jump relaxation. A single relaxation time in the 10 to 90 ms range was noted for each solution. This time depended upon the concentration of both neurophysin and hormone and increased with increasing pH. The formation rate constants (+/- SE) for the interaction of neurophysin I dimer with the protonated form of oxytocin and vasopressin at pH 7.4 in 0.1 M KNO3 and 25 degrees C were 2.8 (+/- 0.4) x 10(6) and 2.3 (+/- 0.5) x 10(6) M-1 s-1, respectively; the dissociation rate constants were 11 and 15 s-1, respectively.For neurophysin II dimer, formation rate constants were 6.0 (+/- 0.2) x 10(6) and 2.4 (+/- 0.3) x 10(6) M-1 s-1; dissociation rate constants were 24 and 16 s-1 for oxytocin and vasopressin, respectively. Formation rate constants for the interaction of neurophysin monomer with protinated hormone were approximatley an order of magniment with circular dichorism and pH titration studies which indicate that this interaction occurs between a negatively charged carboxyl group on the neurophysin and a protonated alpha-amino group on the hormone. Our results indicate that oxytocin and vasopressin bind with greater affinity to the neurophysin dimer than the monomer and that the binding of oxytocin and vasopressin in neurophysin dimer than the monomer and that the binding of oxytocin and vasopressin in neurophysin dimer at pH 7.4 and concentrations between 10(-4) and 10(-5) M is nearly identical for each hormone.
The CRF-like activity of peptides related to vasopressin and oxytocin was estimated using a semi-automated in vitro bioassay. Rat pituitary halves were incubated for 1 h with the test material in 1.0 ml of Krebs-Ringer bicarbonate buffer. The ACTH released from the pituitary tissue was estimated using adrenal quarters in an automated superfusion system. The pituitary tissue was standardized with median eminence extract, and adrenal tissue was standardizeed with ACTH. Vasopressin and its analogues release ACTH in order of their pressor potency. Most of the ring or tail fragments of oxytocin and vasopressin did not stimulate the release of ACTH. In some experiments, deaminopressinamide and pressinoic acid had CRF-like activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.