| Summary: | The effect of surfactants on the hydrolysis of achiral and chiral substrates by crude and purified porcine pancreatic lipase (PPL; EC 3.1.1.3) has been studied. Rather than accelerating the reactions, surfactants slowed down ("inhibited") the reactions relative to the rate in the absence of surfactant, despite effective emulsification of the substrate. Surfactants varied in the extent to which the reaction was inhibited and inhibition occurred below the critical micelle concentration of surfactants. Inhibition was accompanied by a loss of enantioselectivity with the crude enzyme but not the purified enzyme, indicating the presence of more than one activity in the crude PPL preparation. In general, there would seem to be no advantage to be gained from the use of surfactants in the hydrolysis of compounds of low water solubility with lipolytic enzymes; the use of an immiscible cosolvent is more effective. The pyruvate decarboxylase (EC 4.1.1.1) from Zymomonas mobilis strain CP4 ATCC 31821 was purified from recombinant Escherichia coli harbouring the plasmid pLOI295, which contained the gene coding for the enzyme. The purified recombinant enzyme catalysed acyloin condensations with a number of aldehyde acceptors. The substrate specificity of the Zymomonas enzyme was very similar to that observed with the enzyme from Saccharomyces carlsbergensis. However, the Zymomonas enzyme was found to catalyse the formation of acyloins from acetaldehyde at a rate four orders of magnitute greater than that observed with yeast enzyme. By comparing the stereochemistry of acyloin condensations catalysed by the Zymomonas and yeast enzymes, differences in the architecture of the active sites of these closely related enzymes have emerged.
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