Carbon sources, amino acids

All human tissues are capable of synthesizing the nonessential amino acids, amino acid remodelling and conversion of non-amino-acid carbon skeletons into amino acids and other derivatives that contain nitrogen. However, the liver is the major site of metabolism of nitrogenous compounds in the body. Dietary proteins are the primary source of essential amino acids (or nitrogen). Digestion of dietary proteins produces amino acids, which are absorbed through epithelial cells and enter the blood. Various cells take up these amino acids that enter the cellular pools. 

Figure 7.66 The heme moiety of the hemoglobin molecule showing the binding of the oxygen molecule to the iron atom. As shown in the diagram, carbon monoxide binds at the same site. Abbreviation His, side chain of the amino acid histidine. Source From Ref. 18.

McCarthy, M. D., Benner, R., Lee, C., Hedges, J. I., and Fogel, M. L. (2004). Amino acid carbon isotopic fractionation patterns in oceanic dissolved organic matter An unaltered photoautotrophic source for dissolved organic nitrogen in the ocean Marine Chemistry 92(1-4), 123-134. 

Ketone bodies are the major fuel for the heart. Glucose is the major energy source of the brain, and the liver obtains most of its energy from the oxidation of amino acid carbon skeletons. 

When the carbon skeleton of alanine is derived from glucose, the efflux of alanine from skeletal muscle and its uptake by liver provide no net transfer of amino acid carbon to the liver for gluconeogenesis. However, some of the alanine carbon is derived from sources other than glucose. Which amino acids can provide carbon for alanine formation (Hint See Fig. 42.9.)... 

A metabolic process involving the transfer of an amino group (NH ) from one compound to another. This is one process which makes possible the synthesis of a limited number of amino acids—nonessential amino acids. Carbon skeletons for this process are produced through various intermediates of carbohydrate metabolism. A new amino acid can be produced when an amino group (NH ) is transferred from an amino acid to the carbon skeleton. The deaminated molecule—past amino acid—can be used as an energy source. 

Semifermentation Process. In this process, the metaboHc intermediate in the amino acid biosynthesis or the precursor thereof is added to the medium, which contains carbon and nitrogen sources, and other nutrients required for growth and production, and the metaboHte is converted to the... 

Further efficient fermentative methods for manufacture of riboflavin have been patented one is culturing C. famata by restricting the carbon source uptake rate, thereby restricting growth in a linear manner by restriction of a micronutrient. By this method, productivity was increased to >0.17 g riboflavin/L/h (63). The other method, using Bacillus subtilis AJ 12644 low in guanosine monophosphate hydrolase activity, yielded cmde riboflavin 0.9 g/ L/3 days, when cultured in a medium including soy protein, salts, and amino acids (64). 

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

In the Strecker synthesis an aldehyde is converted to an a-amino acid with one more carbon atom by a two-stage procedure in which an a-fflnino nitrile is an intenne-diate. The a-fflnino nitrile is fonned by reaction of the aldehyde with ffliimonia or an fflTtmonium salt and a source of cyanide ion. Hydrolysis of the nitrile group to a carboxylic acid function completes the synthesis. 

Analysis of carbon compounds—even amino acids—from extraterrestrial sources might provide deeper insights into this mystery. John Cronin and Sandra Pizzarello have examined the enantiomeric distribution of unusual amino acids obtained from the Murchison meteorite, which struck the earth on September 28, 1969, near Murchison, Australia. (By selecting unusual amino... 

Fatty acids with odd numbers of carbon atoms are rare in mammals, but fairly common in plants and marine organisms. Humans and animals whose diets include these food sources metabolize odd-carbon fatty acids via the /3-oxida-tion pathway. The final product of /3-oxidation in this case is the 3-carbon pro-pionyl-CoA instead of acetyl-CoA. Three specialized enzymes then carry out the reactions that convert propionyl-CoA to succinyl-CoA, a TCA cycle intermediate. (Because propionyl-CoA is a degradation product of methionine, valine, and isoleucine, this sequence of reactions is also important in amino acid catabolism, as we shall see in Chapter 26.) The pathway involves an initial carboxylation at the a-carbon of propionyl-CoA to produce D-methylmalonyl-CoA (Figure 24.19). The reaction is catalyzed by a biotin-dependent enzyme, propionyl-CoA carboxylase. The mechanism involves ATP-driven carboxylation of biotin at Nj, followed by nucleophilic attack by the a-carbanion of propi-onyl-CoA in a stereo-specific manner. 

An interesting and important fact is that almost all amino acids isolated from proteins L-configuration have the L-configuration at the a-carbon, although some amino acids isolated from microbiological sources are the mirror image isomers, ie in the D-configuration. We shall consider amino add stereochemistry in more detail in section 8.3. 

One of the commercial methods for production of lysine consists of a two-stage process using two species of bacteria. The carbon sources for production of amino acids are corn, potato starch, molasses, and whey. If starch is used, it must be hydrolysed to glucose to achieve higher yield. Escherichia coli is grown in a medium consisting of glycerol, corn-steep liquor and di-ammonium phosphate under aerobic conditions, with temperature and pH controlled. 

Microbial insecticides are very complex materials in their final formulation, because they are produced by fermentation of a variety of natural products. For growth, the bacteria must be provided with a source of carbon, nitrogen, and mineral salts. Sufficient nutrient is provided to take the strain of choice through its life cycle to complete sporulation with concomitant parasporal body formation. Certain crystalliferous bacilli require sources of preformed vitamins and/or amino acids for growth. Media for growing these bacilli may vary from completely soluble, defined formulations, usable for bench scale work, to rich media containing insoluble constituents for production situations (10,27). Complex natural materials such as cottonseed, soybean, and fish meal are commonly used. In fact, one such commercial production method (25) is based on use of a semisolid medium, a bran, which becomes part of the final product. 

Amino acids are the building blocks of proteins, which have long chainlike molecules. They are oxidized in the body to urea, carbon dioxide, and liquid water. Is this reaction a source of heat for the body Use the information in Appendix 2A to predict the standard enthalpy of reaction for the oxidation of the simplest amino acid, glycine (NH2CH2COOH), a solid, to solid urea (H2NCONH2), carbon dioxide gas, and liquid water ... 

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