Stopped-flow investigation of nitrated bovine neurophysin monomer binding to oxytocin

By use of stopped-flow kinetic data, we have measured the kinetics of mononitrated neurophysin I monomer binding to oxytocin. The association constant was 1.3(+/-0.3) x 10(5) M-1s-1 and the dissociation rate constant was 2.0(+/-0.5)s-1 for protonated oxytocin binding. Both rates are significantly slower than those observed for neurophysin dimer. These data suggest that the binding process by which the monomer binds oxytocin is not identical to that of dimer.