Polymerizing equilibria in neurophysin.

1. Evidence for the occurrence of a rapidly polymerizing equilibrium system in freshly prepared aqueous solutions of porcine neurophysin has been obtained by frontal and zonal analysis of gel-filtration elution patterns.2. Elution volumes increased with decreasing protein concentration and derivative analysis of fronts suggested the existence of different polymerizing forms varying in relative proportion with protein concentration.3. In the presence of lysine vasopressin, the results suggested a shift of the equilibrium in favour of higher polymerizing forms.4. In the presence of Ca(2+) elution patterns became characteristic of a monodisperse system of relatively high molecular weight. The effect of Ca(2+) did not survive removal of the ion and was not reproduced by Mg(2+).5. Evidence for a slowly developing polymerization of neurophysin in aqueous solution has been obtained in experiments with solution prepared 24 hr before subjection to gel-filtration.6. A model is proposed for the description of the binding of lysine vasopressin to porcine neurophysin.