Amino acids from glucose

Equation for the Synthesis of Aspartate from Glucose Write the net equation for the synthesis of aspartate (a nonessential amino acid) from glucose, carbon dioxide, and ammonia. 

B. In the synthesis of these three amino acids from glucose, serine is produced from the glycolytic intermediate phosphoglyceric acid. Arginine is produced from the TCA cycle intermediate cc-ketoglutarate, and aspartate by transamination of oxaloacetate. Therefore, glyceraldehyde 3-phosphate is the only common intermediate. 

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

Since much less glucose is required by the brain, the rate of gluconeogenesis falls and hence the rate of protein degradation falls. In the obese, the energy provided from the oxidation of glncose that has been provided by amino acids from protein degradation is as little as 5% of the total (it is much higher in the lean see below). 

The net results of these actions are most apparent in the fasting state, when the supply of glucose from gluconeogenesis, the release of amino acids from muscle catabolism, the inhibition of peripheral glucose uptake, and the stimulation of lipolysis all contribute to maintenance of an adequate glucose supply to the brain. 

The photoelectrochemical synthesis of amino acids from simple molecules has also been reported. Low efficiencies were observed in the conversion of mixtures of methane, ammonia and water to several amino acids on platinized TiOz Amino acids and peptides were reported when glucose replaced methane as the carbon source in a parallel experiment Higher quantum efficiencies (20-40%) were observed in the conversion of alpha-keto acids or alpha-hydroxy acids to the corresponding alpha-amino acids Moderate levels of enantiomeric selectivity (optical yields of about 50%) were reported when chiral starting materials were employed. Photoinduced Michael-like reactions were observed when alpha, beta unsaturated acids were used as substrates for the amino acid synthesis... 

Depletion of ATP is caused by many toxic compounds, and this will result in a variety of biochemical changes. Although there are many ways for toxic compounds to cause a depletion of ATP in the cell, interference with mitochondrial oxidative phosphorylation is perhaps the most common. Thus, compounds, such as 2,4-dinitrophenol, which uncouple the production of ATP from the electron transport chain, will cause such an effect, but will also cause inhibition of electron transport or depletion of NADH. Excessive use of ATP or sequestration are other mechanisms, the latter being more fully described in relation to ethionine toxicity in chapter 7. Also, DNA damage, which causes the activation of poly(ADP-ribose) polymerase (PARP), may lead to ATP depletion (see below). A lack of ATP in the cell means that active transport into, out of, and within the cell is compromised or halted, with the result that the concentration of ions such as Na+, K+, and Ca2+ in particular compartments will change. Also, various synthetic biochemical processes such as protein synthesis, gluconeogenesis, and lipid synthesis will tend to be decreased. At the tissue level, this may mean that hepatocytes do not produce bile efficiently and proximal tubules do not actively reabsorb essential amino acids and glucose. 

FIGURE 1-10 The organic compounds from which most cellular materials are constructed the ABCs of biochemistry. Shown here are (a) six of the 20 amino acids from which all proteins are built (the side chains are shaded pink) (b) the five nitrogenous bases, two five-carbon sugars, and phosphoric acid from which all nucleic acids are built (c) five components of membrane lipids and (d) o-glucose, the parent sugar from which most carbohydrates are derived. Note that phosphoric acid is a component of both nucleic acids and membrane lipids. 

Separating Biomolecules In studying a particular biomolecule (a protein, nucleic acid, carbohydrate, or lipid) in the laboratory, the biochemist first needs to separate it from other biomolecules in the sample—that is, to purify it. Specific purification techniques are described later in the text. However, by looking at the monomeric subunits of a biomolecule, you should have some ideas about the characteristics of the molecule that would allow you to separate it from other molecules. For example, how would you separate (a) amino acids from fatty acids and (b) nucleotides from glucose ... 

In cellular metabolism, groups of enzymes work together in sequential pathways to carry out a given metabolic process, such as the multireaction breakdown of glucose to lactate or the multireaction synthesis of an amino acid from simpler precursors. In such enzyme systems, the reaction product of one enzyme becomes the substrate of the next. 

Coleman, W. M., and Chung, H. L. (2002). Pyrolysis GC-MS analysis of Amadori compounds derived from selected amino acids and glucose. /. Anal. Appl. Pyrolysis 62, 215-223. 

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