Correlation of the kinetics of aggregation and inactivation of L-glutamate dehyrogenase during drying and particle formation of a levitated microdroplet

Measurement of single droplet drying in the acoustic levitator has been used to detect a correlation between the kinetics of aggregation and inactivation of the model protein l-glutamate dehydrogenase (GDH) during drying and particle formation. The droplet drying was performed at one set of conditions: drying gas temperature = 60 degrees C; drying gas relative humidity = 1%, and drying gas velocity = 0.5 L/min. A centrifugation technique was used to remove insoluble aggregates from the rehydrated microparticles removed from the levitator chamber. Size exclusion chromatography could then be used to quantify the contents of nonaggregated native protein. During the constant-rate drying period up to the critical point of drying, there was retention of nonaggregated native structure. Only after the critical point of drying has been reached, a rapid decline in nonaggregated native content was observed owing to formation of insoluble aggregates. No sign of a soluble trimer of GDH was found. The kinetics of this behavior correlates closely with the kinetics of inactivation of the same enzyme in levitated microdroplets from the literature, i.e., retention of activity up to the critical point and rapid loss of activity after the critical point. The novelty of this work is that such a correlation between aggregation and inactivation can be detected during drying and particle formation on both sides of the critical point of drying.