ABSTRACT
Living systems orchestrate an ensemble of structural and functional hierarchy of metabolic networks in order to regulate homeostasis (DeBerardinis et al. 2008; De la Fuente et al. 2006; Digman et al. 2009; Havlin et al. 1999; Ramanujan et al. 2008; Stanley et al. 1999; Wallace 1999). A useful guide to understand this complex labyrinth of energy landscapes is to exploit steady-state approximation, which states that under homeostatic conditions, the rate of generation of any excess metabolite/ cofactor is equal to the rate of such perturbation removal. In this paradigm, the function of external/ internal stimuli is to enable living systems to explore new steady states by means of transient perturbations. Unfavorable conditions during this exploration process may aect the bioenergetics of the living system reversibly or irreversibly. ese changes form the basis of onset of disease processes and various pathophysiology. In the realm of spatial dimensions, a complete theoretical understanding of cellular metabolism is not a realistic goal due to the multitude of players and interactions among them. Experimental investigation is also not straightforward for the same reason. Figure 9.1 illustrates a simple example of NADH oxidation that has an inuence on a relatively intricate relationship between the most fundamental bioenergetic pathways in a cell. Historically, most of the enzyme activities have been studied in isolated conditions; these cell-free systems oered an analytical perspective of the various enzymes studied (e.g., binding or dissociation rates and saturation concentration). Most of the prevailing methods of interrogating energy metabolism in living systems have
9.1 Introduction ......................................................................................201 9.2 Experimental Methods ....................................................................203
