Metabolic strategies

Oxidation-reduction potential (or redox potential, E) is the potential of compounds to accept electrons and is by convention measured relative to that of hydrogen. Thus E is very negative for NADPH (a strong reductant) but positive for 02 (a strong oxidant). Standard redox potentials (Eo values in volts) refer to standard conditions (1M redox components) at neutral pH (pH 7). The standard free energy change at pH 7 for a particular redox reaction (AGo ) is given by  

In the so-called light reactions of photosynthesis electrons (e-) are donated to the chain from H20 and ultimately accepted by NADP+ to yield NADPH. The difference between the Eo values of the NADPH/NADP+ (-0.32 V) and H20/i 02 (+0.82 V) half reactions (electron acceptor minus electron donor) is — 0.32 0.82 V = —1.14V and accordingly AGo = — rcFAEo = +52.6 kcal mol-1 for the overall reaction  

This overall endergonic reaction is driven by absorbed solar energy in an extraordinarily efficient process (efficiency c. 40%). [In Disturbing the Universe, eminent physicist Freeman 

Dyson speculated on the properties of a highly efficient, self-repairing, self-replicating, photosynthetic. machine for space colonization - and could not get past plants]. The photosynthetic ETC involves two ETC-linked light absorbing photosystems (photosystems I and II) and is described by the so-called Z scheme. Electron flow in downhill noncyclic and cyclic sections of the chain is coupled to ATP synthesis by noncyclic and cyclic photophosphorylation, respectively. 

Carbohydrate is then oxidized back to C02 and H20 by plant cells and by plant-consuming eukaryotes (animals and fungi) and prokaryotes (bacteria), this exergonic process being mechanistically coupled to the endergonic formation of ATP, the so-called energy currency of living cells. 

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GL Amidon, GD Lessman, RL Elliot. Improving intestinal absorption of water-insoluble compounds A membrane metabolism strategy. J Pharm Sci 69 1363, 1980. 

Pfeifer, B., Hu, Z., Licari, P. and Khosla, C. (2002) Process and metabolic strategies for improved production of Escherichia coli-derived 6-deoxyerythronolide B. Applied and Environmental Microbiology, 68, 3287-3292. 

Continuum of metabolic strategies. AnAnP, anaerobic anoxygenic photosynthesis OP, oxygenic photosynthesis AAnP, aerobic anoxygenic photosynthesis RP/PC, rhodopsin and other pigments HT, heterotroph DOM, dissolved organic matter. Source-. From Filer, A. (2006). Applied Environmental MIoroblology, 42(12), 7431-7437. 

Metabolic Strategies 227 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway 242 The Tricarboxylic Acid Cycle 282 Electron Transport and Oxidative Phosphorylation 305 Photosynthesis 330 Structures and Metabolism of Oligosaccharides and Polysaccharides 356... 

Chapter 11 A comprehensive description of basic metabolic strategies that govern substrate and energy flow in metabolic pathways. 

The standard hallmark of fermentation is the accumulation of partially metabolized anaerobic end products. This is an inefficient metabolic strategy because a lot of potential chemical energy is still retained in the end products being formed moreover, these are often noxious and therefore at high levels may well... 

Matter (Flow) Balance, Metabolic Strategy and Estimation of Loss Processes (Exit Order) Within Autocatalytic Biochemical Cycles... 

An evolutionary perspective raises the important question What are the implications and/or potential benefits of restricted transsulfuration A key feature of neuronal cells is their ability to live for an entire lifespan without dividing, which is crucial for long-term retention of information in the form of synaptic connections within neural networks. If a neuron divides, it would lose all of its synapses and all of its information content, so a metabolic strategy must exist that keeps neurons out of the cell division cycle. Oxidative stress normally restricts neuronal division (Kruman, 2004), and limiting transsulfuration provides a mechanism by which neurons can indefinitely sustain a moderate level of oxidative stress. Thus, it can be proposed that the unique pattern of sulfur metabolism adopted by the brain may be critical for sustaining retention of information and for neuronal survival over the lifespan. 

Part of the metabolic strategy of the cancer cell appears to involve an increase in the pathways directed toward nucleotide synthesis, which is required for rapid cell division. 

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