THE EFFECT OF POLYOL COMPOUNDS ON THE THERMOSTABILITY OF PENICILLIN-GACYLASE FROM A MUTANT OF ESCHERICHIA-COLI ATCC-11105

The effects of the 15 polyol compounds on the thermostability of penic illin G acylase (PGA) from a mutant of Escherichia coli ATCC 11105 wer e investigated. PGA solutions containing glucose, sucrose, mannose, ad onitol, sorbitol or xylitol at 1 M concentration showed an initial act ivity rate (IAR) higher than 3. The IAR values of these six sugars at 50 degrees C increased with their concentrations in PGA solution. The investigations on half-life times and stabilization factor (SF) values of PGA at 45 and 50 degrees C, in the presence of these compounds, sh owed a tendency for the half-life and SF of the enzyme, at 50 degrees C, to increase with the OH/C ratios of polyol compounds. Sucrose and g lucose were the only two compounds having higher SF values at 50 degre es C than at 45 degrees C. Sucrose showed almost twice the half-life o f glucose and was selected as the best stabiliser of PGA activity agai nst thermal inactivation. PGA showed almost the same pH and temperatur e activity profiles in both presence and absence of sucrose. K-m and V -m values decreased with the increasing sucrose concentrations, with a greater decrease in K-m values.