Oxidation of amino acids

N-Bromoamino acids form within seconds after mixing aqueous bromine and the amino acid in dilute aqueous solution (ref. 6), but are not stable end products of the reaction. Thus, Friedman and Morgulis (ref. 7) found that the oxidation of amino acids by hypobromite gives aldehydes and nitriles with one carbon atom less than the original amino acid, ammonia and CO2 (Scheme 1). The proportions of aldehyde and nitrile depend on the basicity of the medium, aldehyde formation being favoured by more basic conditions. 

The origin of many of the components of black tea aroma has been studied. Aldehydes are produced by catechin quinone oxidation of amino acids. Enzymic oxidation of carotenoids during manufacture generates ionones and their secondary oxidation products such as theaspirone and dihydroactinidolide. Oxidation of linoleic acid is responsible for the formation of trans-2-hexenal.82... 

Klein and Olsen126 studied the action of kojic acid on the enzymic oxidation of amino acids by the liver and kidney of rats. Low concentrations of kojic acid in vitro inhibited the oxidation of a number of D-amino acids, L-phenylalanine, and a few related compounds. Kojic acid was found to compete with D-amino acid oxidase for the substrate. 

Chemical changes include posttranslational modifications including glycosy-lation, phosphorylation, disulfide bond formation and exchange (scrambling), proteolysis or hydrolysis, and deamidation or oxidation of amino acids.4... 

Because of the efficiency of this process, the anodic oxidation of amino acid precursors can serve as an excellent method for generating chiral building blocks for synthesis. For example (Scheme 17, Eq. 1) [39], the anodic oxidation of (45) was accomplished at a platinum anode using an undivided cell. An acetate nucleophile was used to trap... 

In fact, these two processes are metabolically linked. The oxidation generates ATP whereas gluconeogenesis utilises this ATP. Consequently, in the well-fed human, gluconeogenesis is essential for oxidation of amino acids, otherwise oxidation is limited by the need to utilise the ATP (Chapter 8). The reactions in which amino acids are converted to compounds that can enter the gluconeogenic pathway are described in Chapter 8. The position in the gluconeogenic pathway where amino acids, via their metabolism (Chapter 8), enter the pathway is indicated in Figure 6.23. 

A consequence of the oxidation of amino acids is that the amino group is lost to the system, mainly through the formation and excretion of urea. Of the urea produced, the proportion which is excreted in the urine varies depending on the. .. metabolic activity of the colonic micro flora. 

By analogy with the biogenesis of oximes via oxidation of amino acids or biogenic amines, the biosynthetic pathway for insertion of the ketoxime function into the antibiotic, nocardicin A (18), was shown to be dependent on the oxidation of the corresponding primary amine precursor of 18 by cytochrome PTSO ". Similarly, the formation of the ketoxime bond of verongamine (17) is attributed to the oxidation of a primary amine precursor . 

The purpose for the 1998 study was to assess the ability of and determine the means whereby member facilities identify and solve problems in peptide synthesis 10 The potential for oxidation of amino acids such as methionine is always a concern for peptide chemists and biomedical researchers. A peptide mixture containing 70% correct peptide and 30% oxidized peptide was prepared and sent to member facilities to determine if the oxidized methionine would be detected (see Table 1). In addition to the oxidized peptide, a reverse synthesized peptide was sent to the participants. In previous studies, peptides had been submitted which had been synthesized in the reverse order and if only HPLC and mass spectrometric analyses was performed, the reverse synthesis would not be identified. Therefore, two peptides were designed with the second in the reverse order with two substitutions to equal the mass of the first peptide. These two peptides were readily separated by HPLC. The second peptide was sent to the laboratories, but the laboratories were given the first sequence and asked if the correct peptide had been made. Out of 20 participating laboratories ... 

The liver also receives some ammonia via the portal vein from the intestine, from the bacterial oxidation of amino acids. Whatever its source, the Nib generated in liver mitochondria is immediately used, together with C02 (as HCO3) produced by mitochondrial respiration, to form carbamoyl phosphate in the matrix (Fig. 18-1 la see also Fig. 18-10). This ATP-dependent reaction is catalyzed by carbamoyl phosphate synthetase I, a regulatory enzyme (see below). The mitochondrial form of the enzyme is distinct from the cytosolic (II) form, which has a separate function in pyrimidine biosynthesis (Chapter 22). 

The silver(II)-catalyzed decarboxylation of carboxylic acids was noted in Section 54.2.2.2. The oxidation of amino acids is thought to occur by a similar process. 

The oxidation of amino acids is considered to contribute little to the overall energy metabolism in parasitic flatworms, but amino acids are necessary as precursors of protein synthesis for normal growth and reproduction. 

Hawkins CL, Pattison DI, Davies MJ (2003) Hypochlorite-Induced Oxidation of Amino Acids, Peptides and Proteins. Amino Acids 25 259... 

The renal pressor mechanism—renin and hypertensin—acts in acute hypertension and in acute renal ischemic states, but apparently not in chronic hypertension. The other mechanisms shown to be active in chronic hypertension are vasoexcitor-vasodepres-sor material relationship pherentasin, a pressor substance found only in human hypertension amines resulting from the insufficient oxidation of amino acids, which are increased in human hypertension and norepinephrine (Sympathin E), which largely reproduces the hemodynamic picture of chronic hypertension. Most of the known pressor substances, with the notable exception of norepinephrine, come from disturbances of, or are extracted from, the kidneys. The large number of pressor substances which have been obtained suggests that many may represent different stages of metabolism of certain parent substances, and that their effectors may be fewer in number and simpler in structure. The chemical identification and purification of most of these substances leave much to be desired, and their phafmacology has in most cases been inadequately studied. The whole problem, however, may soon become simplified. 

A. Knowles and S. Gumani, A study of the methylene blue-sensitized oxidation of amino acids, Photochem. Photobiol. 16... 

Macrocyclic hypervalent iodine trimer 145 was prepared directly from the oxidation of amino acid 143 [Eq. (117)] [226] self-assembly of the monomeric A3-iodane 144 directed by secondary bonding between iodine and oxygen atom of the amino acid fragment is responsible for the formation of the trimer 145, in which iodine atoms have the pentagonal planar geometry. 

Several studies have measured DFAA concentrations and turnover (see Chapter 4 and Munster, 1993), but here we concentrate on those that compare DFAA uptake with bacterial production. The fraction of bacterial production supported by DFAA is one index for the relative importance of amino acids, not only in supporting bacterial growth but also in the overall flux of DOM. ( Flux is used here to indicate both production and uptake in a quasi-steady state.) If DOM concentrations are constant, DOM production will equal total uptake rates by microbes there is no evidence of photo-oxidation of amino acids and of the other compounds discussed here (see Chapter 10). Total uptake includes respiration and assimilation into biomass. Here assimilation is defined as the appearance of a radioactive compound in cells (both cellular LMW and HMW pools) respiration is excluded. 

The synthesis of unnatural amino acids and peptides is of great interest since it offers the possibility to design new biologically active protein analogues. One of the possible interesting transformations is side chain oxidation of amino acids, for which MTO can be used. It is reported that various /V-Boc protected amino acids such as methionine (Met), cysteine (Cys), and tryptophan (Trp) can be oxidized with the MT0/H202 system [108]. 

Pantoja, S. and Lee, C. (1994) Cell-surface oxidation of amino acids in seawater. Limnol. Oceanogr. 39, 1718-1726... 

While the complete oxidations of fats and carbohydrates yield C02 + H20, the complete oxidation of amino acids yields C02 + H20 and as well as ammonia. Three fates of this so-called nitrogen waste product are common in animals it can be excreted into the outside medium (ammonotelism, which is common in many aquatic animals) it can be excreted as uric acid (uricotely, common in reptiles and birds) or, it can be excreted as urea (common... 

Hydroxyl radicals are probably the most toxic for microorganisms [30], They promote peroxidation of polyunsaturated phospholipid components of the lipid membrane and induce disorder in the cell membrane [31]. The damage of the outer membrane increases the permeability to ROSs. This process is possible thanks to a sufficient lifetime of ROSs generated at the Ti02 surface. ROS diffusion was studied by Fujishima et al. Their experiments demonstrated the bactericidal effect of irradiated Ti02 film on E. coli even at the distance of 50pm from the film [21], Furthermore, oxidative perforation of the cellular membrane allows the photocatalyst nanoparticles to penetrate the interior of the cell, causing severe, efficient oxidation of the cell content [27,32], ROSs are responsible for oxidation of amino acids, peptides [33], enzymes [34], and nucleic acids [32, 35-37]. Destruction of... 

Nitric oxide is an unstable gas and, if exposed to the air, it quickly oxidizes to nitrogen dioxide, NO2 (a brown gas). This helps it to overcome its odd electron unstable structure. However, in the closed environment of the body, this process does not occur and so the NO carries out its unique roles within the body s cells. Its production is probably a result of oxidation of amino acids or proteins. Nitric oxide has been implicated in the biochemistry of virtually every mammalian organ system, including inflammatory and degenerative diseases. It is present in the blood and other parts of the body and there are very small quantities in the brain. These concentrations are so small that it is only in recent years that it has been discovered following the development of sensitive analytical instruments. 

Fig. 1. a-Oxidation of amino acids. Hydroxyl radical (or other reactive radical) abstracts hydrogen atom from the a-carbon. The C-centered free radical formed may react with other amino acid residues or dimerize in the absence of oxygen, which leads to protein aggregation. In die presence of oxygen the carbon-centered radical forms peroxyl radical. Reduction of peroxyl radical leads to protein hydroperoxide. Decomposition of hydroperoxide leads to formation of carbonyl compounds via either oxidative deamination or oxidative decarboxylation. Oxidation of the new carbonyl group forms a carboxyl group. 

D20. Drozdz, R., Naskalski, J. W., and Sznajd, J., Oxidation of amino acids and peptides in reaction with myeloperoxidase, chloride and hydrogen peroxide. Biochim. Biophys. Acta 957, 47-52 (1988). 

Figure 5. Oxidations of amino acids in proteins with peroxide (16)...

D-Amino and L-amino acid-selective electrodes are based on the biocatalytic oxidation of amino acids ... 

As the model suggests, the dietary need for amino acids is determined by the rates of depletion of the free amino acid pool by oxidation or synthesis of protein. During steady state conditions, the contribution to the free pool from dietary intake and protein breakdown should be exactly balanced by the flux out of the pool to synthesis and oxidation. Any condition that increases deposition of protein in the body or the rate of amino acid oxidation should produce an increased need for protein. For example, muscle hypertrophy is dependent on a positive balance of the protein turnover process. If synthesis of protein exceeds the catabolism of protein, then muscle mass will increase and the free amino acid pool would be depleted. Thus, a net increase in protein requires an increase in intake or a decrease in oxidation. Likewise, the same arguments hold for an increase in oxidation of amino acids. 

The mechanism that produces increased amino acid oxidation during exercise is unknown. White and Brooks (29) demonstrated a relationship of amino acid oxidation to use oT blood glucose. Concomitant with increases in the intensity of exercise and leucine oxidation, the oxidation of glucose and alanine increased. These data in combination with the earlier reports of increased flux of leucine to skeletal muscles and alanine from muscles to the liver suggest that the oxidation of amino acids may be linked to the need for glucose and to generation of substrates for gluconeogenesis. 

The impact of aerobic exercise on protein requirements remains uncertain. Exercise clearly can disrupt protein metabolism, both protein turnover and amino acid oxidation. However, it remains to be determined if these effects are acute effects of exhaustive exercise or if moderate exercise in trained individuals still produces increased oxidation of amino acids. 

Subsequently, the functions of the vitamin were better established and requirements for the vitamin were set. Riboflavin is an Integral part of two coenzymes, flavin-5 -phosphate (FMN) and flavin adenine dinucleotide (FAD), which function in oxidation/reductlon reactions. Indeed, riboflavin is an enzyme cofactor which is necessary in metabolic processes in which oxidation of glucose or fatty acid is used for production of adenosine triphosphate (ATP) as well as in reactions in which oxidation of amino acids is accomplished. The minimum requirement for riboflavin has been established as that amount which actually prevents the signs of deficiency. A range of intakes varying from 0.55 to 0.75 mg/day of riboflavin has been established as the minimum amount which is required to prevent appearance of deficiency signs. 

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