Metabolic efficiency

Homeostatic regulation of metabolic efficiency (i.e., caloric intake required to maintain body weight constant to maintain constant ratios of energy expenditure/ conservation). 

Comish-Bowden, A. (1983). Metabolic efficiency Is it a useful concept Biochem. Soc. Trans. 11, 44-45. 

COMPARTMENTATION ENSURES METABOLIC EFFICIENCY SIMPLIFIES REGULATION... 

The existence of various isoforms of many of the enzymes involved with phase I and phase II reactions has been noted above. Key enzymes are also subject to variation by genetic polymorphisms so there may be considerable difference in the metabolic efficiency between individuals and between different ethnic groups. Such genetic differences account for most the variability we see between individuals capacity to metabolise certain drugs. For example, refer to Section 6.4.3. 

Oligodendrocytes are present in the CNS as well and wrap around axons to form a myelin sheath. Myelin wraps into concentric layers that spiral around the axon. Gaps in the oligodendrocytes are the nodes of Ranvier, where the membrane maintains contact with extracellular fluid. The nodes serve to propagate the action potential in myelinated axons. Schwann cells perform an analogous function, myelinating axons in the peripheral nervous system. Not all neurons are myelinated, but myelination increases the metabolic efficiency of action potentials. Demyelination of neurons produces deficits in neuronal conduction, as is seen in multiple sclerosis. 

Prokaryotes have the capacity to rapidly adapt to changes in their chemical environment. Proteins needed for growth are normally synthesized at levels sufficient to support maximal growth rate on a given substrate. In Nature, however, the cells are usually exposed to a mixture of nutrients, and complex regulatory networks guarantee a hierarchical utilization of the substrates, guided by metabolic efficiency. 

Taking into consideration the main pressures channeling the evolution toward metabolic efficiency, that is, increasing free energy dissipation and energetic efficiency, one may single out... 

Enzymes with related functions often are compartmentalized into specific organelles, a process that enhances metabolic efficiency in various ways. First, the higher concentrations of enzymes and intermediates resulting from... 

Dulloo AG, Girardier L. 24 hour energy expenditure several months after weight loss in the underfed rat Evidence for a chronic increase in whole-body metabolic efficiency. Int J Obes Relat Metab Disord 1993 17 115-123. 

Hochachka, P.W. (1993a). Adaptability of metabolic efficiencies under chronic hypoxia in man. In Surviving Hypoxia, pp. 127-135, ed. P.W. Hochachka, P.L. Lutz, T. Sick, M. Rosenthal, and G. van den Thillart. Boca Raton, Fla. CRC Press. 

The reaction that gives chemical energy to heat engines in cars (hydrocarbon oxidation) has to obey the Carnot cycle efficiency limitation (I - 7 , y7),igh).With around body temperature (37 °C), the metabolic would have to be 337 °C to explain this metabolic efficiency in terms of a heat engine. Thus, the body energy conversion mechanism cannot use this means to get the energy by which it works. 

Causes of malnutrition include (7.) reduced quantity and quality of nutrition, (2.) maldigestion and malabsorption, (3.) accelerated protein breakdown and protein loss as well as reduced protein synthesis (PEM), 4.) increased energy requirement, especially in the case of complications, and (5.) metabolic disturbances (e.g. insulin resistance, sympathicotonia, loss of metabolic efficiency), (s. p. 741)... 

North, W.J., 1954. Size distribution, erosive activities and gross metabolism efficiency of the marine intertidal snails Littorina planaxis and L. scutulata. Biol. Bull., 106 185— 197. 

Cumene is absorbed readily via the inhalation route in man and animals, and is metabolized efficiently, within the body, to water-soluble metabolites that are excreted into the urine. The secondary alcohol 2-phenyl-2-propanol and its conjugates are major metabolites. Neither cumene nor its metabolites are likely to accumulate within the body. Based on controlled studies in humans, the average retention of inhaled cumene in the respiratory tract was 50%. 

Andreasen et al (1993) ... aspects of brain structure that reflect quality rather than quantity of brain tissue complexity of circuitry, dendritic expansion, number of synapses, thickness of myelin, metabolic efficiency, or efficiency of neurotransmitter production, release, and reuptake. Factors such as these would facilitate the speed and efficiency of information transfer within the brain as well as expand its capacity, so that multiple tasks of multiple kinds could be performed simultaneously. The greater volume of grey matter can be postulated to reflect a greater number of nerve cell bodies and dendritic expansion a greater number of neuronal connections presumably enhances the efficiency of computational processing in the brain. ... 

Most short-term experimental and observational research concludes that intense UVR, particularly UV-B (280-315 nm), damages cellular structures, decreases metabolic efficiency and reduces growth or survival of individuals [1,47]. Direct inhibition of algal photosynthesis and growth appears to be greatest when... 

Orzechowska-Juzwenko K, Wronska-Nofer T, Wiela A, et al. 1985. Phenazone biotransformation as a maker of metabolic efficiency of the liver in rabbits chronically exposed to carbon disulfide. Naunyn Schmiedeberg Arch Pharmacol 330 R13. 

Greater metabolic efficiency (better oral absorption, slower excretion)... 

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