LAUSR

Here we report the effect of polyethyleneglycol (PEG6000) induced molecular crowding (MC) on the catalytic activity and thermal stability of from Kluyveromyces lactis β-galactosidase (β-Gal). The β-Gal catalyzed hydrolysis of o-nitrophenyl-β-D-galactopyranoside followed a michaelian kinetics at [PEG6000] ≤ 25%w/v and positive cooperativity at higher concentrations (35%w/v PEG6000). Compared with dilute solutions, in the MC media β-Gal exhibited stronger thermal stability as shown by the increase in the residual activity recovered after pre-incubation at high temperatures (e.g.45°C) as well as by the slower inactivation kinetics. Considering the effects of water thermodynamic activity on the reactions kinetics and protein structure, and the effect of the exclusion volume on protein conformation, we suggest that changes in protein oligomerization state and hydration could be the responsible for the behavior observed at the highest MC levels assayed. These results could be relevant and should be taken into account in industrial food processes applying β-Gal from K.lactis.