A 50th order reaction predicted and observed for sickle hemoglobin nucleation.

Sickle hemoglobin polymerization exhibits a striking sensitivity to initial concentration, with characteristic reaction times that exhibit 30th power dependence on concentration. This extraordinary reaction order is encompassed by a novel double nucleation mechanism that predicts 50th power dependence of the homogeneous nucleation rate. Using a technique that allows individual homogeneous nucleation events to be monitored, we have measured a concentration dependence of 47+/-, in excellent agreement with the predictions of the model. Absolute nucleation rates agree with predictions as well.