Tyrosine flavins

Lu, C. Y. Lui, Y.Y. (2002). Electron transfer oxidation of tryptophan and tyrosine by triplet states and oxidized radicals of flavin sensitizers a laser flash photolysis study. Biochimica et Biophysica Acta (BBA) - General Subjects, Vol. 1571, No.l, (May 2002), pp. 71-76, ISSN 0304-4165... 

Fig. 43.1 Prosthetic groups in oxidoreduc-tases (1 flavin adenine dinucleotide (FAD) 2 thio-tyrosine 3a (R=H) nicotinamide adenine dinucleotide 3b (R = PO ) ...

In contrast to the flavin-dependent monoamine oxidases, SSAO/VAP-1 has evolved to hydroxylate a tyrosine residue in the active site which is further oxidized to the quinone state by oxygen in the presence of copper ion releasing hydrogen peroxide [28-30]. The primary amine in the substrate (R-NH2, Scheme 1) forms a Schiff-base with the quinone carbonyl group, which through a series of steps ultimately releases the aldehyde product. 

This enzyme catalyzes the covalent insertion of a tyrosine at the C-terminal glutamate of the tubulin a subunit to effect the posttranslational synthesis of a peptide bond (Flavin et al., 1982 Thompson, 1982). The role of this modification reaction remains to be established... 

Amine oxidases catalyze the oxidative deamination of both xenobiotic and biogenic amines, and thus have many critical biological functions. Two distinct classes differ in the nature of their prosthetic groups [1]. The flavin-(FAD flavin adenine dinucleotide)-dependent amine oxidases include monoamine oxidases (MAO A and B) and polyamine oxidases. Amine oxidases not containing FAD, the so-called semicarbazide-sensitive amine oxidases (SSAO), include both plasma amine oxidases and tissue amine oxidases. These contain quinonoid structures as redox cofactors that are derived from posttranslationally modified tyrosine or tryptophan side chains, topaoquinone frequently playing this role [2]. 

Tire tetrahydrobiopterin formed in this reaction is similar in structure to a reduced flavin. The mechanism of its interaction with 02 could reasonably be the same as that of 4-hydroxybenzoate hydroxylase. However, phenylalanine hydroxylase, which catalyzes the formation of tyrosine (Eq. 18-45), a dimer of 451-residue subunits, contains one Fe per subunit,113 313i whereas flavin monooxygenases are devoid of iron. Tyrosine hydroxylase416 193 and tryptophan hydroxylase420 have very similar properties. All three enzymes contain regulatory, catalytic, and tetramerization domains as well as a common Fe-binding motif in their active sites.413 421 4213... 

Aromatic compounds arise in several ways. The major mute utilized by autotrophic organisms for synthesis of the aromatic amino acids, quinones, and tocopherols is the shikimate pathway. As outlined here, it starts with the glycolysis intermediate phosphoenolpyruvate (PEP) and erythrose 4-phosphate, a metabolite from the pentose phosphate pathway. Phenylalanine, tyrosine, and tryptophan are not only used for protein synthesis but are converted into a broad range of hormones, chromophores, alkaloids, and structural materials. In plants phenylalanine is deaminated to cinnamate which yields hundreds of secondary products. In another pathway ribose 5-phosphate is converted to pyrimidine and purine nucleotides and also to flavins, folates, molybdopterin, and many other pterin derivatives. 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

Urocanic acid DNA, RNA Tyrosine Phenylalanine Tryptophan NADH, nicotinamide Collagen Flavins Bilirubin... 

F26BP, fructose-2,6-bisphosphate FA, fatty acid FAD, fatty acid desaturase FADH2/FAD, reduced/oxidized flavin adenine dinucleotide F -ATPase, ATP synthetase F complex FGF, fibroblast growth factor FGF-RTK, fibroblast growth factor receptor tyrosine kinase Fmet, formylmethionine FMNH2/FMN, reduced/oxidized flavin mononucleotide... 

Most aromatic hydroxylases are either cytochrome- or flavin-dependent enzymes the three enzymes that catalyze hydroxylation of the aromatic amino acids phenylalanine, tyrosine, and tryptophan are apparently unique in... 

In PCMH, two equally efficient pathways for electron transfer from the flavin N5 to the heme iron were identified in GREENPATH calculations. One path follows the tyrosyl covalent link to FAD at the C8-methyl position, whereby electrons can travel from C8M via the Tyr 384 phenolic ether bond, tunnel through the tyrosine ring atoms and make a through-space jump across the subunit interface to the carbonyl oxygen of Ala 49 in the cytochrome (Figure 16). From there the electrons follow backbone... 

In a third pathway, electrons flow from the N1 position of flavin via a hydrogen bond to Gly 305(N), on through backbone to the Tyr 306 side-chain, followed by a jump from the tyrosine hydroxyl to the methyl CMC atom of heme. The path with weakest coupling involves a through-space jump from the flavin 02 to Trp 391, then a jump to Cys 714 SG, which is covalently linked to the heme. 

The photodegradation of pyridoxine is noticeable in sugar and saline infusion solutions, but much less in amino acid infusion solutions. The presence of tyrosine and tryptophan inhibits photodecomposition, whereas flavine mononucleotide accelerates it (84). 

There are three tyrosine residues in Fre, Tyr 35, Tyr 72, and Tyr 116, close to the flavin-binding pocket (Fig. 1.2). Fluorescence lifetime measurements of the wild-type and mutant Fre/flavin complexes showed that electron transfer from Tyr 35 to the excited FAD isoalloxazine is responsible for the fluorescence quenching [6]. The average positions of the bound FAD and the three tyrosine residues of the protein are shown in the figure. To study the fluctuations in the... 

There are three hydroxylation reactions on the ubiquinone biosynthetic pathway. All three oxygens are derived from molecular oxygen 1198] and heme is not required [199]. This suggests that these hydroxylations proceed by a mechanism analogous to that of the flavin dependent tyrosine hydroxylase (Fig. 42) [14]. 

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