Journal
APPLIED BIOCHEMISTRY AND BIOTECHNOLOGY
Volume 169, Issue 3, Pages 786-794Publisher
HUMANA PRESS INC
DOI: 10.1007/s12010-012-0003-3
Keywords
Protein denaturation; Chaotropic solute; Model enzyme; Steady-state kinetics; Polyol; Enzyme flexibility
Funding
- Biotechnology and Biological Sciences Research Council [BBF0034711]
- Department of Agriculture and Rural Development Northern Ireland
- Nuffield Foundation
- BBSRC [BB/F003471/1] Funding Source: UKRI
- Biotechnology and Biological Sciences Research Council [BB/F003471/1] Funding Source: researchfish
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During alcoholic fermentation, the products build up and can, ultimately, kill the organism due to their effects on the cell's macromolecular systems. The effects of alcohols on the steady-state kinetic parameters of the model enzyme beta-galactosidase were studied. At modest concentrations (0 to 2 M), there was little effect of methanol, ethanol, propanol and butanol on the kinetic constants. However, above these concentrations, each alcohol caused the maximal rate, V (max), to fall and the Michaelis constant, K (m), to rise. Except in the case of methanol, the chaotropicity of the solute, rather than its precise chemical structure, determined and can, therefore, be used to predict inhibitory activity. Compounds which act as compatible solutes (e.g. glycerol and other polyols) generally reduced enzyme activity in the absence of alcohols at the concentration tested (191 mM). In the case of the ethanol- or propanol-inhibited beta-galactosidase, the addition of compatible solutes was unable to restore the enzyme's kinetic parameters to their uninhibited levels; addition of chaotropic solutes such as urea tended to enhance the effects of these alcohols. It is possible that the compatible solutes caused excessive rigidification of the enzyme's structure, whereas the alcohols disrupt the tertiary and quaternary structure of the protein. From the point of view of protecting enzyme activity, it may be unwise to add compatible solutes in the early stages of industrial fermentations; however, there may be benefits as the alcohol concentration increases.
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