Citric acid, synthesis

Presented in Figs. 1 and 2 are data relating to external aind internal mass transfer for the case of citric acid synthesis. 

The catalytic function of coenzyme A in citric acid synthesis. J. biol. 

Citric Acid Synthesis Three-Point Attachment Theory Aconitase... 

Other compounds which interfere with the synthesis of the cellular membranes, for example some antibiotics such as penicillin and some surfactants, have a similar effect even when the concentration of biotin is not limiting. This manipulation of the conditions under which the organism grows to ensure the efficient excretion of the L-glutamic acid is reminiscent of the control of citric acid synthesis in A. niger (section 6.2.2.2). 

Studies of the enzymic mechanism of the citric acid synthesis by Stern and Ochoa have directly shown that citric acid, and not aconitic acid, is the primary product. It had earlier been thought that the mechanism of citric acid synthesis might be similar to that of the reaction leading in vitro to the formation of citric acid from oxalacetic and pyruvic acid in the presence of hydrogen peroxide, where oxalocitramalic acid is an intermediate. Martins, however, found this substance to be metabolically inert in animal tissue. Stern and Ochoa found that aqueous extracts of acetone-dried pigeon liver formed citrate when acetate, oxalacetate, ATP, coenzyme A, and Mg or Mn ions were present. Thus the condensation reaction is preceded by the decarboxylation of pyruvic acid and the formation of an active form of acetate. This active acetate, as discussed below, is acetyl coenzyme A. 

Zhang G, Yang G, Ma JS (2006) Versatile framework solids constructed from divalent transition metals and citric acid synthesis, crystal structures and thermal behaviors. Cryst Growth Des 6 375-381... 

Actually, an interest in the anhydride of citric acid synthesis started when Repta et al. [488] and Robinson et al. [489] analyzed behaviour of acetic anhydride and... 

Wilkes JB, Wall RG (1980) Reaction of dinitrogen tetraoxide with hydrophilic olefins synthesis of citric acid and 2-hydroxy-2-methylbutanedioic acids. J Org Chem 45 247-250 Saigsyan MS, Mkrtumyan SA, Gevorkyan AA (1989) Citric acid synthesis. Armyanskii Khim Zh 42 496-505... 

Novell GD, Lipmann F (1950) The catalytic function of coenzyme Ain citric acid synthesis. J Biol Chem 182 213-228... 

Vargas DA, Medina J (eds) (2012) Citric acid synthesis, properties and applications. Nova Publishers, New York... 

Zhou ZH, Wan HL, Tsai KR (1997) Molybdenum(VI) complex with citric acid synthesis and structural characterization of 1 1 ratio citro molybdate K2Na [(Mo2)20(Cit)2] 5H2O. Polyhedron 16 75-79... 

Chemical Synthesis. The chemical synthesis of citric acid was reported in 1880 (27). Since then, many different synthetic routes have been investigated, reported, and patented (28—36). However, none of these have proven to be commercially feasible. 

Glycolysis and the citric acid cycle (to be discussed in Chapter 20) are coupled via phosphofructokinase, because citrate, an intermediate in the citric acid cycle, is an allosteric inhibitor of phosphofructokinase. When the citric acid cycle reaches saturation, glycolysis (which feeds the citric acid cycle under aerobic conditions) slows down. The citric acid cycle directs electrons into the electron transport chain (for the purpose of ATP synthesis in oxidative phosphorylation) and also provides precursor molecules for biosynthetic pathways. Inhibition of glycolysis by citrate ensures that glucose will not be committed to these activities if the citric acid cycle is already saturated. 

Figure 29.1 An overview of catabolic pathways for the degradation of food and the production of biochemical energy. The ultimate products of food catabolism are C02 and H2O, with the energy released in the citric acid cycle used to drive the endergonic synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) plus phosphate ion, HOPO32-.

The primary fate of acetyl CoA under normal metabolic conditions is degradation in the citric acid cycle to yield C02. When the body is stressed by prolonged starvation, however, acetyl CoA is converted into compounds called ketone bodies, which can be used by the brain as a temporary fuel. Fill in the missing information indicated by the four question marks in the following biochemical pathway for the synthesis of ketone bodies from acetyl CoA ... 

Generally, NAD-linked dehydrogenases catalyze ox-idoreduction reactions in the oxidative pathways of metabolism, particularly in glycolysis, in the citric acid cycle, and in the respiratory chain of mitochondria. NADP-linked dehydrogenases are found characteristically in reductive syntheses, as in the extramitochon-drial pathway of fatty acid synthesis and steroid synthesis—and also in the pentose phosphate pathway. 

The amino acids are required for protein synthesis. Some must be supplied in the diet (the essential amino acids) since they cannot be synthesized in the body. The remainder are nonessential amino acids that are supplied in the diet but can be formed from metabolic intermediates by transamination, using the amino nitrogen from other amino acids. After deamination, amino nitrogen is excreted as urea, and the carbon skeletons that remain after transamination (1) are oxidized to CO2 via the citric acid cycle, (2) form glucose (gluconeogenesis), or (3) form ketone bodies. 

Pathways are compartmentalized within the cell. Glycolysis, glycogenesis, glycogenolysis, the pentose phosphate pathway, and fipogenesis occur in the cytosol. The mitochondrion contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and of oxidative phosphorylation. The endoplasmic reticulum also contains the enzymes for many other processes, including protein synthesis, glycerofipid formation, and dmg metabolism. 

Citrate is isomerized to isocitrate by the enzyme aconitase (aconitate hydratase) the reaction occurs in two steps dehydration to r-aconitate, some of which remains bound to the enzyme and rehydration to isocitrate. Although citrate is a symmetric molecule, aconitase reacts with citrate asymmetrically, so that the two carbon atoms that are lost in subsequent reactions of the cycle are not those that were added from acetyl-CoA. This asymmetric behavior is due to channeling— transfer of the product of citrate synthase directly onto the active site of aconitase without entering free solution. This provides integration of citric acid cycle activity and the provision of citrate in the cytosol as a source of acetyl-CoA for fatty acid synthesis. The poison fluo-roacetate is toxic because fluoroacetyl-CoA condenses with oxaloacetate to form fluorocitrate, which inhibits aconitase, causing citrate to accumulate. 

The citric acid cycle is not only a pathway for oxidation of two-carbon units—it is also a major pathway for interconversion of metabolites arising from transamination and deamination of amino acids. It also provides the substtates for amino acid synthesis by transamination, as well as for gluconeogenesis and fatty acid synthesis. Because it fimctions in both oxidative and synthetic processes, it is amphibolic (Figure 16—4). 

Aminotransferase (transaminase) reactions form pymvate from alanine, oxaloacetate from aspartate, and a-ketoglutarate from glutamate. Because these reactions are reversible, the cycle also serves as a source of carbon skeletons for the synthesis of these amino acids. Other amino acids contribute to gluconeogenesis because their carbon skeletons give rise to citric acid cycle... 

The Citric Acid Cycle Takes Part in Fatty Acid Synthesis (Figure 16-5)... 

Figure 16-5. Participation of the citric acid cycle in fatty acid synthesis from glucose. See also Figure 21-5.

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