Fermentative metabolism

When excess substrate interferes with growth and/or product formation. One example is the production of baker s yeast. It is known that relatively low concentrations of certain sugars repress respiration and this will make the yeast cells switch to fermentative metabolism, even under aerobic conditions. This, of course, has a negative effect on biomass yield. When maximum biomass production is aimed at, fed batch cultures are the best choice, since the concentration of limiting sugar remains low enough to avoid repression of respiration. 

Aoyama, K., Uemura, I., Miyake, J., Asada, Y. 1987. Fermentative metabolism to produce hydrogen gas and organie compounds in a cyanobacterium Spirulina platensis. J Ferment Bioeng 83 17-20. 

Short-chain acids accumulate.under anoxic conditions/-which favor fermentative metabolism of bacteria. Such phytotoxins nay damage the plant directly or predispose plants to infection by pathogens. However plant residues nay also be used as substrates for beneficial micro-organisms to produce plant nutrients, soil conditioners, and plant protection chemicals. There is scope to promote the beneficial microbial effects against the harmful by soil management and by inoculation. 

Substrate level phosphorylation refers to those reactions associated with the generation of energy by the transfer of phosphate groups in metabolism, and is exemplified by fermentative metabolism where it is the sole source of energy (e.g. yeast and bacteria growing in anaerobic conditions). 

If energy is generated solely by substrate-level phosphorylation, as with anaerobic fermentative metabolism of bacteria and yeast, then the yield is more tightly linked to the amount of energy generated. Generally 10 to 12 kg of cell dry matter can be synthesised per kmol of ATP generated in metabolism. 

The distinctive feature of CM is the exploitation of grape-cell AM. Intact berries quickly shift from oxidative to fermentative metabolism under anaerobic conditions (atmospheres with oxygen contents <1%). 

Bouhnik, Y., Flourie, B., D Agay-Abensour, L., Pochart, P., Gramet, G., Durand, M., and Rambaud, J.-C., Administration of transgalacto-oligosaccharides increases fecal bifidobacteria and modifies colonic fermentation metabolism in healthy humans, J. Nutr., Ill, 444—448, 1997. 

Microbes capable of carrying out fermentations are classified as either facultative or obligate anaerobes. Facultative anaerobes, such as the enterobacteria, utilize 02 if and when it is present, but if it is absent, they carry out fermentative metabolism. In contrast, obligate anaerobes are unable to synthesize the components of electron transport systems consequently, they cannot grow as aerobes. Moreover, many of the obligate anaerobes cannot even tolerate oxygen and perish in air these organisms are referred to as strict anaerobes. 

The design rules for fermentative metabolism in bacteria are few in number and are widely expressed in the microbial world. Firstly, the fermentation process always involves the partial oxidation of substrate, although there is a tremendous diversity in choice of substrate. Almost any organic compound can be fermented by some microorganism somewhere. Secondly, the oxidative reaction or reactions must always be balanced by subsequent reductive reactions in order to allow sustained func-... 

The past four years have witnessed major changes in concepts of anaerobic fermentative metabolism and photosynthesis, due mainly to recognition of the key role of ferredoxin. Ferredoxin is a non-heme iron protein, containing no flavin, which carries the most energetic electrons in metabolism. The cellular function and chemistry of ferredoxin are described in this chapter. This is not intended to be an all-inclusive review of the literature pertaining to ferredoxin. Certain aspects of the subject are discussed in the earlier articles of Mortenson (71), Valentine (106), and... 

Recent years have witnessed increasing interest in the biology, chemistry, and physics of electron-transferring non-heme iron proteins. This class of protein serves as an oxidation-reduction component in various biological functions involved in anaerobic fermentative metabolism, photosynthesis, and hydroxylation reactions. 

R. P. Gfeller and M. Gibbs. 1985. Fermentative metabolism of Chlamydomonas reinhardtii. II. Role of plastoquinone, Plant Physiol. 77, 509-511. 

The biological aging of wines has aroused increasing interest in recent years, as reflected in the large number of papers on this topic over the last decade. Biological aging in wine is carried out by flor yeasts. Once alcoholic fermentation has finished, some Saccharomyces cerevisiae yeast races present in wine switch from a fermentative metabolism to an oxidative (respiratory metabolism) and spontaneously form a biofllm called flor on the wine surface. Wine under flor is subject to special conditions by effect of oxidative metabolism by yeasts and of the reductive medium established as they consume oxygen present in the wine. These conditions facilitate... 

Gfeller, R.P. and Gibbs, M., Fermentative metabolism of Chlamydomonas reinhardtii. I. Analysis of fermentative products from starch in dark and light, Plant Physiol., 75, 212, 1984. 

Lactate dehydrogenase is closely associated with the final step in fermentative metabolism conversion of pyruvate to lactate- Citrate synthase is closely associated with oxidative metabolism, because this enzyme catalyzes the introduction of acetyl groups into the Krebs cycle. Continued operation of the Krebs cycle is dependent on the continued transfer of electrons from reduced NAD and FAD to the respiratory chain, which catalyzes the reduction of Oi to HjO. Table 4.14 lists lactate dehydrogenasc/citrate synthase activity ratios for muscles that contain a large proportion of white or red muscle fibers. The data demonstrate that the ratio is relatively high in white cell muscles but low in red cell muscles. 

Fatty acid synthetase, 183 Fatty acid transport, 215-216,12D, 777-774 Falty liver, 293 alcoholism, 250-251 choline deficiency, 3l7 Fatty streak, 360, 636 Fecal blood test, 84 Feedback inhibition, 256 Feeding center, brain, 103-104 Fenton reaction, 627.635,903 Fermentative metabolism, 159,181-182, 233-243... 

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