Proteome-wide Amino aCid and Elemental composition(PACE) analysis is a novel and informative way of interrogating the proteome.The PACE approach consists of in silico decomposition of proteins detected and quantifed in a proteomics experiment into 20 amino acids and fve elements(C,H,N,O and S),with protein abundances converted to relative abundances of amino acids and elements.The method is robust and very sensitive;it provides statistically reliable differentiation between very similar proteomes.In addition,PACE provides novel insights into proteome-wide metabolic processes,occurring,e.g.,during cell starvation.For instance,both Escherichia coli and Synechocystis down-regulate sulfur-rich proteins upon sulfur deprivation,but E.coli preferentially down-regulates cysteine-rich proteins while Synechocystis mainly downregulates methionine-rich proteins.Due to its relative simplicity,flexibility,generality and wide applicability,PACE analysis has the potential of becoming a standard analytical tool in proteomics. Proteome-wide Amino aCid and Elemental composition (PACE) analysis is a novel and informative way of interrogating the proteome. PACE approach consists of in silico decomposition of proteins detected and quantified in a proteomics experiment into 20 amino acids and fve elements (C, H, N, O and S), with protein abundances converted to relative abundances of amino acids and elements. The method is robust and very sensitive; it provides a very reliable differentiation between very similar proteomes.In addition, PACE provides novel insights into proteome- wide metabolic processes, occurring, eg, during cell starvation. For instance, both Escherichia coli and Synechocystis down-regulate sulfur-rich proteins upon sulfur deprivation, but E. coli preferentially down-regulates cysteine-rich proteins while Synechocystis mainly downregulates methionine-rich proteins.Due to its relative simplicity, flexibility, generality and wide applicability, PACE analysis has the potential of becoming a standard analyt ical tool in proteomics.