Propranolol binds to B-adrenergic receptors with a K of 8.9 x 10-9 M. What concentration of propranolol would be required to achieve a 50% reduction in the binding of the receptor agonist isoproterenol if the agonist concentration is 4.9 nM and its dissociation constant for the receptor is 4.8 x 10-8 M? i nM