THERMAL-STABILITY OF LOW-MOLECULAR-WEIGHT UROKINASE DURING HEAT-TREATMENT .2. EFFECT OF POLYMERIC ADDITIVES

Turbidimetric or light scattering assays can be used to determine the extent of aggregation in protein formulations. Using low molecular wei ght urokinase (LMW-UK) as a model protein, the effect of polymeric add itives on heat-induced aggregation was evaluated. Previous work has sh own that under 60 degrees C heat treatment, LMW-UK initially denatures and the unfolded protein associates to form soluble aggregates. Event ually, these aggregates associate to form a precipitate. The effects o f polymers on the initial aggregation phase was examined. Hydroxyethyl (heta) starch, polyethylene glycol 4000, and gelatin were found to be effective, concentration-dependent inhibitors of aggregation, whereas polyvinylpyrrolidone (PVP) and polyethylene glycol 300 were ineffecti ve. Overall, the effect of polymeric additives on the stability of the rmally-stressed LMW-UK can be accounted for by preferential exclusion of the solute from the surface of the protein.