ABSTRACT
In contrast to DNA-and RNA-based analysis, direct quantification of protein levels at a global level is technically difficult at present, mostly because of the chemical complexity of proteins relative to DNA and RNA molecules (Bertone and Snyder, 2005; Maercker, 2005). The experimental conditions for measuring DNA copy numbers or RNA abundance are nearly the same for all nucleic acids; in contrast, the large range of optimal conditions that are specific for each protein molecule renders the establishment of high-throughput protein assays difficult. Development of highthroughput technologies in the field of proteomics has, however, led to a number of different array-based formats capable of screening a number of interactions including protein-antibody, protein-protein, protein-ligand, protein-drug, and enzymesubstrate. The capture array where ligand-binding reagents, usually antibodies, are used to target molecules in mixtures such as plasma or tissue extracts probably represents the most commonly applied protein array.
