Relationship between the initial rate of protein aggregation and the lag period for amorphous aggregation

Lag period is an inherent characteristic of the kinetic curves registered for protein aggregation. The appearance of a lag period is connected with the nucleation stage and the stages of the formation of folding or unfolding intermediates prone to aggregation (for example, the stage of protein unfolding under stress conditions). Discovering the kinetic regularities essential for elucidation of the protein aggregation mechanism comprises deducing the relationship between the lag period and aggregation rate. Fändrich proposed the following equation connecting the duration of the lag phase (tlag) and the aggregate growth rate (kg) in the amyloid fibrillation: kg = const/tlag. To establish the relationship between the initial rate of protein aggregation (v) and the lag period (t0) in the case of amorphous aggregation, the kinetics of dithithreitol-induced aggregation of holo-α-lactalbumin from bovine milk was studied (0.1 M Na-phosphate buffer, pH 6.8; 37 °C). The order of aggregation with respect to protein (n) was calculated from the dependence of the initial rate of protein aggregation on the α-lactalbumin concentration (n = 5.3). The following equation connecting v and t0 has been proposed: v1/n = const/(t0 − t0,lim), where t0,lim is the limiting value of t0 at high concentrations of the protein.

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