Urocortin: slower dissociation than corticotropin releasing factor from the CRF binding protein

We report on a comparison of the kinetics of [I-125[Tyr(0)]corticotropin re leasing factor (CRF) and [I-125][Tyr(0)]urocortin binding to the CRF bindin g protein (CRF-BP) at physiological temperature. The association rates of [ I-125][Tyr(0)]urocortin or [I-125[Tyr(0)]CRF binding to the CRF-BP were sim ilar. The half time of association for [I-125][Tyr(0)]urocortin was 3.2 min and for [I-125][Tyr(0)]CRF, 2.6 min. [I-125[Tyr(0)]urocortin dissociated f rom the CRF-BP but the rate of dissociation was slower than for [I-125][Tyr (0)]CRF. The half time for dissociation of [I-125][Tyr(0)]urocortin was 131 min and for [I-125][Tyr(0)]CRF, 64 min. This slower dissociation indicates that the CRF-BP may be more effective in clearing urocortin than CRF. (C) 1999 Elsevier Science B.V. All rights reserved.