RESUMO
To date, lyophilized samples are rarely utilized in proteomics experiments. This is most likely because researchers are concerned about inducing cross-linking of proteins via amide bonds, leading to artefactual charge modification and thus resulting in irreproducible results and bad gels. Indeed, it is known that lyophilization can cause crosslinking. The potential reaction is a reaction of free amino groups of a protein (N-terminal alpha-amino groups and epsilon-amino groups from lysine) with the reducing group of sugar molecules. The rate and extent of this reaction depends on the sugar content of the sample, the efficiency of lyophilization process, the residual water content of the material and the storage temperature. Lyophilization is a cheap, practical and safe alternative for the storage and transportation of samples prior to protein extraction, separation and quantification via 2DE, when care is taken (i) to dry the samples to the lowest practicable moisture content, (ii) to transport and store them under water- and airtight conditions and (iii) to avoid heating of the sample.