Tyrosine, oxidation

NOTE Rats were administered five SC doses of MDA (10 mg/kg). MDMA (10 mg/kg). or METH (15 mg/kg), one dose every 6 hours, and killed 18 hours after the last dose. Results are presented as the means SEM, expressed as a percent of saline control. Control values were TH, 2645 163 nmol tyrosine oxidized/g fissue/hr and TPH, 45.0 3.5 nmol 14C02 fiberated/g tissue/hr... 

Marquez and Dunford [193] have studied the kinetics of L-tyrosine oxidation by MPO. They measured the rate constants for the reactions of MPO compounds I and II with tyrosine and dityrosine and found out that, comparing with HRP, LPO, and TPO, MPO is the most effective catalyst of tyrosine oxidation at physiological pH (Table 22.1). Furthermore, the rate constant for Reaction (9) with tyrosine turns out to be comparable with that for Reaction (16), confirming the possibility for tyrosine to compete in blood plasma with chloride, which is considered to be the major MPO substrate and a potent oxidizing agent against invading bacteria and viruses. 

Copper oxygenases Tyrosinase Fungal, Tyrosine oxidation... 

The conversion of TV-Boc tyrosinal 140 to the spirolactol 141 with BTIB in aqueous acetonitrile is a useful variant of the tyrosine oxidation (Scheme 41) (96JCS(P1)1385). Similar cyclizations of appropriate... 

Meunier S, Strable E, Finn MG. Crosslinking of and coupling to viral capsid proteins by tyrosine oxidation. Chem Biol 2004 11 319-29. 

Dityrosine, due to its specific fluorescence, is the most-often assayed tyrosine oxidation product (excitation 315-325 nm, emission at 410 120 nm) (H4, P15). 

Also, HPLC methods with electrochemical or fluorescent detection are used (H19, M3). In proteins, dityrosine can be estimated by immunochemical methods employing dityrosine-specific antibodies (K5). Measurements of o,o -dityrosine and o-tyrosine levels in rat urine express dityrosine contents in skeletal muscle proteins, and have been proposed as the noninvasive oxidative stress test in vivo. One should be aware, however, that A-formylkynurenine, also formed in protein oxidation, has similar fluorescence properties as dityrosine (excitation 325 nm, emission at 400-450 nm) (G29). Also, oxidation of mellitin when excited at 325 nm produces an increase in fluorescence at 400—450 nm, despite the fact that mellitin does not contain tyrosine. Oxidation of noncontaining Trp residues ribonuclease A and bovine pancreatic trypsin inhibitor with "OH produces loss of tyrosine residues with no increase in fluorescence at 410 nm (S51). There are also methods measuring the increased hydrophobicity of oxidized proteins. Assays are carried out measuring protein binding of a fluorescent probe, 8-anilino-l-naphthalene-sulfonic acid (ANS). Increase in probe binding reflects increased surface hydrophobicity (C7). 

Each of the photosystems ejects an electron from the excited chlorin complex to a quinone within a nanosecond, followed by electron transfer along chains leading out of the charge separation center within 100 ns. The high potential reaction of Tyr and Mn in PSII is quite rapid, beginning in the simulations on the same time scale as the quinone reduction reaction. However, it has been suggested that tyrosine oxidation may not be rate limited by tunneling, but by H+ transfer (Diner et al., 2001). 

Effect of Fiber Degradation on the Corrosion Solution. Hydrolysis and oxidation of protein and cellulose have been described in the literature primarily with the focus on degradation in industrial processing conditions. In alkaline conditions, amino acids are released from silk in a chain unzipping mechanism in acidic conditions, the scissions are random (8,9). As the polymer deteriorates, free carboxyl and amine end groups are formed. Tyrosine oxidizes to a quinone this reaction gives aged silk its yellow coloration. Amorphous areas of the fiber are attacked first. 

Absorption spectra of phenoxyl radicals derived from biologically important molecules were recorded in numerous cases. The tyrosyl radical was studied by many investigators and its spectrum was used to detect tyrosine oxidation in a protein and to follow intramolecular electron transfer from tyrosine to the tryptophan radical in dipeptides and polypeptides . A number of catecholamines, such as adrenaline and dopa, were also studied by kinetic spectrophotometric pulse radiolysis " ". The absorption spectra of most of these substituted o-semiquinone anion were similar to those of the unsubstituted... 

The intermediate formation of 2,5-dihydroxyphenylpyruvic acid in this conversion has not been proved by isolation. But as this is readily metabolized by tyrosine-oxidizing systems (e.g., 489), unlike the possible alternative intermediate p-hydroxyphenylacetic acid, the pathway is not in doubt. On the other hand, the detailed mechanism of this conversion is probably the major unsolved problem in the study of tyrosine metabolism. 

Uchida, Suzuki, and Ichihara (878) isolated a soluble enzyme system (thereby possibly excluding mitochondrial participation) from rabbit liver, and partially purified it. Two enzymes were involved. The first of these converted p-hydroxyphenylpyruvic acid to 2,5-dihydroxyphenylpyruvic acid. If this enzyme was resolved, vitamin C alone did not restore the activity, but vitamin C and vitamin B12 did. The amount of B12 required was very low, and they suggested that the true enzyme was a Bw derivative, possibly aquocobalamin hydroxide bound to enzyme protein, and that the function of the ascorbic acid was solely to stabilize the reactive form of the coenzyme. This agrees with the work of La Du and Greenberg (524), who considered the role of ascorbic acid to be quite unspecific. Ascorbate increased the rate of tyrosine oxidation in liver preparations but the net consumption was zero, and moreover numerous ene-diols were just as effective on a molar basis. La Du and Greenberg considered that ascorbic acid participates in a cyclic oxidation-reduction and happens to be a substance of the correct oxidation-reduction potential either to participate directly or to protect some other participant. 

A large body of literature exists concerning the measurement of protein oxidation during aging in different models. Most of the studies measure the formation of protein-bound carbonyls [88-108]. Other authors suggested or used other amino acid modifications, like tyrosine oxidation products such as dityrosine, o-tyrosine or nitrotyrosine [109-112], the formation of 5-hydroxyl-2-amino valeric acid [ 113], or methionine sulfoxide formation [112]. Changes... 

We have applied this theoretical formulation [26-28] to a series of PCET reactions. The systems were chosen based on the availability of experimental data that had not yet been fully explained. The systems that will be discussed in this section are iron bi-imidazoline complexes, ruthenium polypyridyl complexes, amidinium-car-boxylate interfaces, DNA-acrylamide complexes, tyrosine oxidation, and the enzyme lipoxygenase. In all cases, the solvent was treated as a dielectric continuum [58, 59]. 

Figure 16.8 Experimental and theoretical data forthe pH dependence of the rates for single electron transfer and PCET in the tyrosine oxidation model shown in Eig. 16.7. The experimental values are denoted with open circles. The theoretical PCET rates are denoted with filled circles, and the theoretical ET rate is represented by a solid line because it is independent of pH. The ET and PTcouplings were fit to the experimental ET rate at pH>10 and PCET rate at pH 7. Reproduced from Ref [63],...

Tyrosine Oxidation (p-Hydroxyphenylpyruvate Oxidase) (Eq. 17) The interruption of tyrosine degradation at the stage of p-hydroxy-phenylpyruvate (pHPP) in scurvy has long been considered Ae clearest evidence of a biochemical role for ascorbic acid. The intmmediate accumulates and is excreted when doses of tyrosine are given to scorbutic man, other primates, and guinea pigs, and to premature infants (K8). 

Oxidation of N-protected tyrosine. Oxidation of an N-protccted tyrosine 1 with CftHsl(OAc)2 in methanol provides a spirolactonc (2), which is converted by treatment with NaHCO, in CHjOH into the exo-hydroindolc 3, a bicyclic system common to various Stemona alkaloids. Actually 1 can be converted directly into 3 by oxidation of 1 in ihc presence of sodium bicarbonate. The conversion of 1 to 3 evidently involves para-hydroxylation of a phenol followed by a highly diastcrcosclcctive intramolecular... 

La Du, 8.N. Zannoni, V.G. The Tyrosine Oxidation System of Liver II Oxidation of p-Hydroxylphenylpyruvic Acid to Homogentisic Acid (1955) 217 777-787... 

Verweij, H., K. Christianse, and J. van Steveninck. 1982. Different pathways of tyrosine oxidation by ozone. Chemosphere 11 721-725. 

Scheme 1 Tyrosine oxidation/reduction pathways in photosystem II...

The most common cause of an elevation of the serum phenylalanine level about 3 mg dl is the transient neonatal delay in the development of the tyrosine oxidizing system (transient neonatal tyrosinemia). This condition, while far more common in low-birth-weight and premature infants, does occur occasionally in full-term infants as weU. The elevation of phenylalanine is secondary to a block in the metabolism of tyrosine. Administration of 100 mg of ascorbic acid will reduce the tyrosine levels, but whether this is necessary is an area of some controversy (Cohn and Roth 1983). 

The immediate electron donor to Chl-ajj" is a tyrosine (6,7). The spectrum of the tyrosine oxidation in the UV (Fig. 5)(7) appears in the ns range simultaneously with that of the re-reduction of Chl-ajj". Tyr extracts an electron from the water splitting enzyme S. 

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