Metabolic flexibility

Microorganisms, particularly bacteria and fungi, have also proved to be a rich source of bioactive molecules such as antibiotics and anticancer agents (Chapter 1). Again, as in the case of plants, an incredibly rich array of microbial species inhabit the earth and their characteristic metabolic flexibility generates an enormous bank of potential pharmaceutical products. Most... 

Figure 9.2. The inherent metabolic flexibility of the isoprenoid pathway leading to the synthesis of some carotenoid pigments. Genes coding for two enzymes capable of acting on carotenoid structures were introduced into Escherichia coli which had already been transformed to give it the capacity to make p,p-carotene. Both of the two introduced new enzymes (one shown with red arrows and the other with blue arrows) acted on multiple substrates because of their lack of specificity. The resulting matrix of transformations means that nine different products can be made by just two tailoring enzymes. (Adapted from Umeno et al. ° who used data from Misawa et al. °)...

Figure 10.1. The gene from Clarkia breweri coding for (S)-linalool synthase (LIS) was added to three different piant species (tomato, petunia and carnation) and each species produced the expected product, S-iinaiooi. However, the existing NP metabolic flexibility in each species aiiowed the novei substance, S-iinaiooi, to be converted to other substances, those substances being different in each species due to the differences in NP metabolism in each plant. ...

Plants must be especially versatile in their handling of carbohydrates, for several reasons. First, plants are autotrophs, able to convert inorganic carbon (as C02) into organic compounds. Second, biosynthesis occurs primarily in plastids, membrane-bounded organelles unique to plants, and the movement of intermediates between cellular compartments is an important aspect of metabolism. Third, plants are not motile they cannot move to find better supplies of water, sunlight, or nutrients. They must have sufficient metabolic flexibility to allow them to adapt to changing conditions in the place where they are rooted. Finally, plants have thick cell walls made of carbohydrate polymers, which must be assembled outside the plasma membrane and which constitute a significant proportion of the cell s carbohydrate. 

To meet these changing circumstances, the liver has remarkable metabolic flexibility. For example, when the diet is rich in protein, hepatocytes supply themselves with high levels of enzymes for amino acid catabolism and gluconeogenesis. Within hours after a shift to a high-carbohydrate diet, the levels of these enzymes begin to drop and the hepatocytes increase their synthesis of enzymes essential to carbohydrate metabolism and fat synthesis. Liver enzymes turn over (are synthesized and degraded) at live to ten times the rate of enzyme turnover in other tissues, such as muscle. Extrahepatic... 

Many fundamental concepts in modem biology have been established through studies on aquatic organisms. Fish are of special interest to research workers, because some of their metabolic features characterized early vertebrates. Fish have also evolved numerous adaptations, which have permitted them not only to survive but also to thrive in recent times. The range of structural and functional adaptations and metabolic flexibility, combined with individual specializations, has resulted in an immense diversity of fish - more than 20 000 species - which greatly exceeds that of amphibians, reptiles, birds and mammals. As the final link in many food chains, fish can be reliable indicators of the condition of complex ecosystems. Studies on fish provide an understanding of the pathways of metabolic substances and of energy transformations in bodies... 

The PPC allows the generation of NADPH reduction equivalents required for cell anabolism, and ribose 5-phosphate molecules for the synthesis of nucleic acids. Alternatively, ribose 5-phosphate can also be generated or transformed into fructose 6-phosphate or glyceraldehyde 3-phosphate, providing metabolic flexibility to the cell, in order to balance the fluxes through these pathways. The flux through the PPC is related to the nucleic acid requirements for DNA duplication or RNA transcription, and could probably be controlled by the cell cycle (Wagner, 1997). 

Smirnoff, N. (Ed.) 1995. Environment and Plant Metabolism Flexibility and Acclimation. BIOS Scientific, Oxford, UK. 

The mammalian liver through its tremendous metabolic flexibility disposes of many toxic substances, including those released from hazardous waste sites, in very few common, polar forms. In a sense we hope to exploit this capability to convert pollutants to polar, involatile forms amenable to direct TSP LC/MS determination. The development of improved means for separation, selective detection and identification of metabolic conjugates in biological fluids has applications in the dosimetry of many toxic substances. Such techniques may be useful in screening exposures to a multitude of compounds simultaneously. 

H. Taegtmeyer, S. Sharma, L. Golfman, M. Van Arsdall, and P. Razeghi, Linking gene expression to function metabolic flexibility in normal and diseased heart, AnnN YAcad Sci 1015,1-12 (2004). 

Once amino acid molecules enter cells, the amino groups are available for synthetic reactions. This metabolic flexibility is effected primarily by transam-... 

Animals are constantly synthesizing and degrading nitrogen-containing molecules such as proteins and nucleic acids. Protein turnover is believed to provide cells with metabolic flexibility, protection from accumulations of abnormal proteins, and the timely destruction of proteins during developmental processes. Ubiquitin is one stress protein that plays an important role in targeting proteins for destruction. 

The process of protein turnover promotes metabolic flexibility, protects a cell from the accumulation of abnormal proteins, and is a key feature of organismal developmental processes. 

E. coli is metabolically flexible and easily genetically manipulated, and this allows it to be competitive for some bioprocesses. The economical production... 

Microbial fuel cells rely on bioelectrochemical reactions driven by microbial metabolism to produce electricity while degrading organic substrates. Pure culture MFC studies with bacteria such as Geobacter and Shewanella have informed researchers on the mechanisms behind extracellular electron transfer (EET), but it is mixed consortium communities that typically produce the most power and have the most metabolic flexibility to handle a variety of substrates and environmental conditions. 

Peguin S, Goma G, Delorme P, Soucaille P (1994) Metabolic flexibility of... 

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