Dtric acid

The realisation that yeasts would produce dtric acid from n-paraffins was veiy attractive in the late 1960 s. Petroleum byproducts were plentiful and very cheap and there was detailed knowledge available on these processes because the use of hydrocarbon-utilising yeasts for single cell protein was well developed. The strategy was to use n-alkane to produce high yields erf dtric add-producing Candida spp. and to harvest two useful end products rather than just one. The process has not been commerdally successful however. Candida spp. produce mixtures of dtric add and isodtric add and the latter is not a useful product. In addition, since 1973 when petroleum prices rose sharply and have in fact continued to rise, the n-paraffins are no longer a cheap substrate. 

For each of the following enzymes in A. rtiger, select metabolites from the list provided that either inhibit or stimulate activity during a) balanced growth and b) during dtric acid accumulation (caused by Mn2 defidency). 

In summary, and regarded at its simplest, A. rtiger degrades suitable carbon sources by glycolysis which is occurring at an uncontrolled rate. There is inevitably an overflow at the pyruvate level which is converted to dtric acid. 

Nitrogen is normally supplied as an ammonium compound in dtric acid fermentations and suffident has to be supplied to enable the effect of manganese deficiency (increased levels of ammonium in the metabolic pool) to occur. Remember that increased metabolic pool ammonium has the effect of releasing the allosteric controls exerted on phosphofructokinase. 

The submerged culture process continues to increase in terms of the percentage of dtric acid produced compared to that produced by the surface culture method. Tower bioreactors are preferred over stirred reactors because they cost less, there is less risk of contamination and they are less limited by size. 

After fermentation, large volumes of spent medium containing dtric acid and mycelium remain. 

Where do you think the dtric acid will be located in the liquid culture ... 

Like in dtric acid production relatively modest aeration rates are required. Stopping aeration for literally a minute or so will permanently arrest product formation. 

The primary function of the dtric acid cycle is oxidation of acetyl CoA to carbon dioxide. The energy released from this oxidation is saved as NADH, FADHj, and guanosine triphosphate (GTP). The overall result of the cyde is represented by the following reaction ... 

Notice that none of the intermediates of the citric add cyde appear in this reaction, not as reactants or as products. This emphasizes an important (and frequently misunderstood) point about the cycle. It does not represent a pathway for the net conversion of acetyl CoA to citrate, to malate, or to any other intermediate of the cyde. The only fate of acetyl CoA in this pathway is its oxidation to CO,. Therefore, the dtric acid cycle does not represent a pathway by which there can be net synthesis of glucose from acetyl CoA... 

The dtric acid cycle is shown in Figure 1-13-1, All the enzymes are in the matrix of the mitochondria except succinate dehydrogenase, which is in the inner membrane. 

Biotin enzymes are believed to function primarily in reversible carboxvlahon-decarboxylation reactions. For example, a biotin enzyme mediates the carboxylation of propionic acid to methylmalonic add, which is subsequently converted to succinic acid, a dtric acid cycle intermediate. A vitamin Bl2 coenzyme and coenzyme A are also essential to this overall reaction, again pointing out the interdependence of the B vitamin coenzymes. Another biotin enzyme-mediated reaction is the formation of malonyl-CoA by carboxylation of acetyl-CoA ( active acetate ). Malonyl-CoA is believed lo be a key intermediate in fatly add synthesis. 

Itaconic acid has been prepared by the distillation of citric acid,2 of aconitic acid,3 and of itamalic add 4 by heating dtric acid with dilute sulfuric acid in a closed tube 5 by treating aconitic acid with water at 1800 6 by heating citraconic acid with sodium hydroxide 7 by heating citraconic anhydride with water at 1500 8 and by heating a concentrated solution of citraconic add at 120-130° in a sealed tube.9... 

The crystal structures of metal complexes of dtric acid have also received much attention. In... 

LiOH 8.3 Gel buffer Tris (46 mAf), dtric acid (7 mAf), 100 ml of electrode buffer, and complete to 1 liter with water adjust to pH 8.3 with 1 Af Tris or 1 Af dtric add. Electrode buffer Lithium hydroxide (50 mAf), boric add (0.19 Af) adjust to pH 8.1 with 1 Af LiOH or 1 Af boric add... 

Mateh each of tiie following statements with a process for dtric acid formaticm using A. mg. ... 

Citric acid, found in citrus fruits, is listed as an inhibitor, and also occurs as a reaction intermediate in the metabolic tricarboxylic acid or dtric acid cycle. Ethanol or ethyl alcohol makes an unexpected appearance as an inhibitor, as does glycerol. The ubiquitous alkaloid ingredient of coffee, better known as caffeine, is listed as an inhibitor (in fact, coffee enemas are sometimes used in folkloric cancer treatments). Creatine, a nitrogenous compound found naturally in the body, is an inhibitor, and is a known anticancer agent, for example, as used with urea in a nuxture called Carbatine. 

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