Amino acids Formation

Iron, tris(hexafluoroacetylacetone)-structure, 1,65 Iron, tris(oxalato)-chemical actinometer, 1,409 photoreduction, 1,471 relief-image-forming systems, 6,125 Iron, tris(l,10-phenanthroline)-absorptiometry, 1,549 racemization, 1,466 solid state, 1,467 structure, 1, 64 lron(III) chloride amino acid formation prebiotic systems, 6,871 Iron complexes acetonitrile. 4,1210 acetylacetone, 2,371 amidines... 

Molybdenum hexafluoride. 3,1412 Molybdenum-iron-sulfur complexes, 4,241 Molybdenum oxide amino acid formation prebiotic systems, 6, 872 Molybdenum storage protein microorganisms, 6, 681 Molybdenum telluride, 3, 1431 Molybdenum tetraalkoxides physical properties, 2, 347 Molybdenum tribromide, 3,1330 Molybdenum trichloride, 3,1330 Molybdenum trifluoride, 3, 1330 Molybdenum trihalides, 3, 1330 bond lengths, 3, 1330 magnetic moments, 3,1330 preparation, 3,1330 properties, 3, 1330 structure, 3,1330 Molybdenum triiodide, 3,1330 Molybdenum trioxide complexes, 3, 1379 Molybdenum triselenide, 3, 143)... 

Amino acid formation in the Urey-Miller experiment and almost certainly in the prebiotic environment is via the Stecker synthesis shown in Figure 8.3. This reaction mechanism shows that the amino acids were not formed in the discharge itself but by reactions in the condensed water reservoir. Both HCN and HCO are formed from the bond-breaking reactions of N2 and H2O in a plasma, which then react with NH3 in solution. The C=0 group in formaldehyde or other aldehydes is replaced by to form NH and this undergoes a reaction with HCN to form the cyano amino compound that hydrates to the acid. The Strecker synthesis does not provide stereo-control over the carbon centre and must result in racemic mixtures of amino acids. There is no room for homochirality in this pathway. 

Amino acid formation was monitored over 24 h by chiral high-performance liquid chromatography (CHIROBIOTIC T column) with samples diluted 10-fold (in H2O) to a suitable concentration. 

This use of a weaker oxidant has several consequences. First, the reaction is readily reversible. Indeed, at neutral pH and with average substrate concentrations, the equilibrium tends to lie toward amino acid formation. Second, since the oxidant is not an ubiquitous oxygen, with a discardable product, but costly NAD(P)", forming NADPH, it becomes essential in any production process to find a way to reclaim or recycle the cofactor. Third, the absence of H2O2 among the products largely removes the concern about further reaction of the oxoacid through oxidative decarboxylation. 

Dietary purines are not an important source of uric acid. Quantitatively important amounts of purine are formed from amino acids, formate, and carbon dioxide in the body. Those purine ribonucleotides not incorporated into nucleic acids and derived from nucleic acid degradation are converted to xanthine or hypoxanthine and oxidized to uric acid (Figure 36-7). Allopurinol inhibits this last step, resulting in a fall in the plasma urate level and a decrease in the size of the urate pool. The more soluble xanthine and hypoxanthine are increased. 

Amino Acid Formation in Submarine Hydrothermal Vents. 78... 

In this review we will consider the different aspects of the prebiotic chemistry of amino acid and peptides. It includes a survey of recent advances in amino acid formation pathways, the question of peptide bond formation considered both from the synthetic point of view and by taking into account the thermodynamic constraints on peptide bond formation and the availability of activated forms of amino acids and/or activating agents. The question of the emergence of the genetic code will be considered in the context of a co-... 

Among protein oxidation products, formation of protein peroxides should be mentioned. Protein peroxidation occurs as a reaction secondary to free-radical attack on amino acid side groups, effecting a carbon-centered free radical of amino acid formation. Such a radical reacts with the oxygen molecule and produces a hydroperoxide radical ... 

Cydo-fSarg) (70) was subjected to further invest ations and was proved to assume the same conformation in crystalline state as in solution, where the peptide bond had a cis-cis-trans-tramtrans-trans sequence. As stated earlier, in cyclic peptides made of N-unsubstituted amino acids, formation of the tum accompanied with intramolecular hydrogen bonds contributes to the stabilization of the ringstruc-... 

This requirement is fulfilled for electric discharges in a reduced atmosphere containing methane, ammonia, and water, as in the original Miller experiment. It has also been observed for atmospheres based on N2 and CO or CO2 on the condition that H2 or methane is also present in snfflcient amonnts (19). A neutral atmosphere (based on N2, CO2, and water) wonld produce much lower yields of organics (by several orders of magnitude). In the absence of other species to be oxidized, the rednction of CO2 reqnires the concomitant thermodynamically nnfavorable conversion of water into O2 (as in photosynthesis). However, even if the atmosphere was nentral when life arose, as nsnaUy believed, the Earth was not nniform with respect to redox state simply becanse the rednced state of the mantle and the high volcanic activity favored the occnrrence of locally rednced environments (for instance, in hydrothermal vents in the oceans). Then, a preservation of the hydrogen content of the early atmosphere or the diversity of environments on the early Earth is likely to have made amino acid formation possible, at least at specific places. 

A strong argument in favor of the involvement of Strecker synthesis is that aldehydes and HCN are among the initial species formed in electric discharge experiments leading to a-amino acid formation. Mechanistic and thermodynamic studies (20) of systems derived from aqueous mixtures containing... 

Taillades J, BeuzeUn I, Garrel L, Tabacik V, Bled C, Commeyras A. A -carbamoyl-a-amino acids rather than free a-amino acids formation in the primitive hydrosphere a novel proposal for the emergence of prebiotic peptides. Orig. Life Evol. Biosph. 1998 28 61-77. 

In the case of A -alkyl amino acids, the oxazohum ion 18 is formed even in the absence of base catalysis because of the electron-donating effect of the A -alkyl group,thus increasing the risk of racemization (Scheme 8). Although proline can be considered as an N-alkylated amino acid, formation of the oxazolium salt is not observed, probably as a consequence of the steric constraints of the five-membered ring which disfavors cyclization.P l As a result, in... 

Although the discovery of amino acid formation was of tremendous significance in establishing that the raw materials of proteins were easy to obtain in a primitive Earth environment, there remained a larger question as to the nature of the origin of genetic materials—in particular the origin of DNA and RNA molecules. 

The formation of these complexes profoundly affects the visible spectrum of TNP-amino acids. This complication is resolved in the spectrophotometric procedure of Plapp et al. (1971) by following TNP-amino acid formation at 367 nm, the isobestic point for e-trinitrophenyl-a-acetyllysine and its sulfite complex. The procedure described by Fields (1971, 1972) exploits the higher extinction coefficient of the sulfite complex at 420 mii. 

Chain-reaction polymerization may be induced by various catalysts. For example, vinyl polymerization (Reaction 5) occurs with free-radical, anionic, or cationic catalysts, as well as with coordinate catalysts (which may be of the anionic or the cationic type) (30, 31). Poly(a-amino acid) formation (Reaction 8) may be carried out with basic catalysts. 

The assay system for measuring transaminase activity contains two amino acids and two oxo-acids. As there is no convenient method for assaying amino acids, formation or consumption of the oxo-acids is measured. Historically,... 

Lacey et al., 1991 Allen and Lacey, 1993 Hashizume and Umeda, 1996 Hashizume and Samuta, 1997 1999 Roujou de Boubee et al., 2002). The biosynthetic pathway of these compounds involves formation of the amide of the appropriate amino acid, formation of a pyrazinone, and methylation as shown in Fie. 4.4 (Murray and Whitfield, 1975). 

Coupling of tRNAs to Amino Acids Formation of Aminoacylated tRNAs (Figure 27.10, Figure 27.11)... 

Phosphorus has more known functions in the animal body than any other mineral element. Together with calcium, phosphorus plays a major role in the formation of bones and teeth, as well as eggshells. It is a component of nucleic acids, which control cell multiplication, growth and differentiation. In combination with other elements, phosphorus has a role in the maintenance of cellular osmotic pressure and the acid-base balance. Energy transfer processes in all living cells involve interconversion of the phosphate-containing nucleotides, adenosine diphosphate (ADP) and ATP, and thus phosphorus participates in all biological events. Other roles include its presence in phospholipids, where it functions in cell-wall structure, fatty acid transport and protein as well as amino acid formation. 

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