How acetaldehyde inactivates microbial lipases. Deprotonated (-NH2) or protonated (-NH3+) amino groups can be generated by lyophilization from buffers of the respective pH. Only deprotonated amino groups are able to form Schiff bases with acetaldehyde; they can induce the formation of intra- and intermolecular cross-links. Furthermore, bases and/or amino compounds (protein-bound amino groups, free amino compounds in the buffer) can catalyze the aldol condensation of acetaldehyde to α,β-unsaturated aldehydes which result in a yellow to brownish-black colour of the respective solution or protein. Finally, the formation of Michael-adducts between the enzyme and the α,β-unsaturated aldehydes leads to inactivation. At lower enzyme concentrations, the inactivation process proceeds fast; whereas fast aggregation of the enzyme at higher concentrations hampers the covalent modification thereby decelerating the inactivation process.
Franken et al. BMC Biochemistry 2011 12:10 doi:10.1186/1471-2091-12-10