Central European Journal of Biology

Cell metabolism is comprised of enzyme-catalyzed biochemical reactions and carrier-mediated transport processes. Taken as a whole, these reactions form interrelated metabolic pathways which are combined into a cellular metabolic network. Metabolic fluxes describe the amount of material chemically converted or transported per time unit and are considered as the key parameters of any metabolic pathway and hence, as the fundamental determinants of cell physiology [1-4]. Changes in metabolic fluxes in response to various types of genetic and environmental perturbations are critical for the metabolic flux control which is a key objective of metabolic engineering [5,6]. On the other hand, enzyme activity is one of the major factors influencing the magnitude of metabolic fluxes in any cell [6]. According to concepts of systems biology, metabolic fluxes are net sums of underlying enzymatic reaction rates represented by integral outputs of three biological quantities which interact at the level of enzyme kinetics: kinetic parameters, enzyme and reactant concentrations [7]. An integrated view on enzymes suggests them as dynamic assemblies whose variable structures are closely related to catalytic functions [8,9]. It is therefore important to extend our knowledge of enzyme sequence, structure, and function relationships [10], as well as to explore coherencies between enzyme activity profiles and metabolic flux distributions in order to understand the physiological dynamics within a cell [2,11]. Amino acid (AA) composition (AAC) is a simplest attribute of proteins among so-called global sequence Cent. Eur. J. Biol. • 8(2) • 2013 • 107-120 DOI: 10.2478/s11535-013-0125-1