The protein complement of a cell or tissue is dynamic and reflects the age, life-cycle, and conditions the cell is subjected to or a specific disease state. It is clear that in most diseases, proteins are subjected to numerous changes including post-translational modifications and/or proteolytic cleavage; equally in certain diseases, there is alteration of protein expression. Messenger ribonucleic acid (mRNA) is the molecule encoding the chemical blueprint for a protein. Yet the micro arrays examining differential expression of mRNA will not provide information on post-translational modification, therefore the only way to assess the impact of the proteins is at the protein level.