Phenylalanine properties

As a p hydroxy derivative of phenylalanine tyrosine has properties similar to those of phenylalanine plus the ability to engage m hydrogen bonding via its —OH group Asparagine and glutamine are not amines they are amides The side chains of both O... 

Different optical enantiomers of amino acids also have different properties. L-asparagine, for example, tastes bitter while D-asparagine tastes sweet (see Figure 8.3). L-Phenylalanine is a constituent of the artificial sweetener aspartame (Figure 8.3). When one uses D-phenylalanine the same compound tastes bitter. These examples clearly demonstrate the importance of the use of homochiral compounds. 

From this discussion it is clear, that, independently of their redox properties, suitably modified electrodes offer themselves for the introduction of diastereo- or enantioselectivity into electrochemistry. Early reports of chiral inductions at modified electrodes include reactions at graphite and SnO surfaces derivatized with monolayers of (S)-(—)-phenylalanine. Asymmetric inductions at the chiral graphite electrode could, however, not be verified in other laboratories even after great efforts... 

Wieder, K.J., Palczuk, N.C., van Es, T., and Davis, F.F. (1979) Some properties of polyethylene glycol Phenylalanine ammonia-lyase adducts./. Biol. Chem. 254, 12579-12587. 

Investigations of the effects of UV- and hypochlorite-induced oxidative modification of 20 amino acids and human serum albumin (HSA) on their antiradical properties showed unexpected results [36], Seven amino acids (cystine, histidine, methionine, phenylalanine, serine, tryptophan, and tyrosine) and HSA developed ACW following oxidation (see examples in Fig. 14). The fresh (produced in 1998) HSA from Serva had no antiradical capacity, but it acquired this quality during irradiation. The out-of-date HSA sample (Dessau, GDR, 1987, expiration date 7/1/1992) showed a remarkable ACW even in an unirradiated state. 

Several studies have been devoted to determine the localization of end-groups in modified polypropylene imine) dendrimers. Goddard et al. [ 157] and Cavallo and Fraternali [158] investigated the properties of the dendritic box, a fifth-generation polypropylene imine) dendrimer functionalized with (t-BOC)-pro-tected L-phenylalanine residues (Figure 16.12a) [159]. 

One of the groups of theories about the origin of the genetic code states that the code has to be the way it is, and is therefore universal, for stereochemical" reasons. In other words, phenylalanine, f. ex. must be represented by the triplets UUU and UUC because phenylalanine is somehow stereochemically related to these two codons 52,53,56,57) This seems likely, since steric fit is an essential property of the processes of replication, transcription and translation. That doesn t mean that one has conclusive evidence for such a statement. It only means that the theoreticians are groping in such a direction. 

A third type of detector is the intrinsic or native fluorescence detector that utilizes native fluorescence properties of amino acids. The sensitivity of this detector is between UV/PDA and LIF detection. The advantage of this technique over pre-labeling is that there is no pre-labeling step required therefore, the sample preparation is relatively simple, and the sensitivity is improved over UV/LIF. However, the intrinsic fluorescence detection relies on the presence of Tryptophan (Try), Tyrosine (Tyr), Phenylalanine (Phe), and this detector has just become commercially available. 

Helical heptad repeat sequences have been reported to be well behaved although they are difficult to characterize by NMR spectroscopy due to spectral overlap. The motifs that have been shown to have native-like properties, and are not highly repetitive, have cores composed of aromatic amino acid side chains of, for example, phenylalanine and tryptophan. In four-helix bundle motifs [1, 2], the /1/la-motif BBAl [5] and the /1-sheet protein Betanova [9], the formation of the folded structure appears to be strongly dependent on such residues although the energetics have not been calculated by substitution studies. As a tentative rule, therefore, the probability of success in the design of a new protein is probably much higher if residues are included that can form aromatic clusters in the core (Fig. 5). 

Koukol J, Conn EE (1961) The metabohsm of aromatic compounds in higher plants. IV. Purification and properties of the phenylalanine deaminase of Hordeum vulgare. 1 Biol Chem 236 2692-2698... 

Tyrosinase is a monooxygenase which catalyzes the incorporation of one oxygen atom from dioxygen into phenols and further oxidizes the catechols formed to o-quinones (oxidase action). A comparison of spectral (EPR, electronic absorption, CD, and resonance Raman) properties of oxy-tyrosinase and its derivatives with those of oxy-Hc establishes a close similarity of the active site structures in these proteins (26-29). Thus, it seems likely that there is a close relationship between the binding of dioxygen and the ability to "activate" it for reaction and incoiporation into organic substrates. Other important copper monooxygenases which are however of lesser relevance to the model studies discussed below include dopamine p-hydroxylase (16,30) and a recently described copper-dependent phenylalanine hydroxylase (31). 

The liver is also the principal metabolic center for hydrophobic amino acids, and hence changes in plasma concentrations or metabolism of these molecules is a good measure of the functional capacity of the liver. Two of the commonly used aromatic amino acids are phenylalanine and tyrosine, which are primarily metabolized by cytosolic enzymes in the liver [1,114-117]. Hydroxylation of phenylalanine to tyrosine by phenylalanine hydroxylase is very efficient by the liver first pass effect. In normal functioning liver, conversion of tyrosine to 4-hy-droxyphenylpyruvate by tyrosine transaminase and subsequent biotransformation to homogentisic acidby 4-hydroxyphenylpyruvic acid dioxygenase liberates CO2 from the C-1 position of the parent amino acid (Fig. 5) [1,118]. Thus, the C-1 position of phenylalanine or tyrosine is typically labeled with and the expired C02 is proportional to the metabolic activity of liver cytosolic enzymes, which corresponds to functional hepatic reserve. Oral or intravenous administration of the amino acids is possible [115]. This method is amenable to the continuous hepatic function measurement approach by monitoring changes in the spectral properties of tyrosine pre- and post-administration of the marker. 

During work on a series of aspartyl dipeptides containing ACC 71 (vide supra, Eq. (28), Sect. 4) at the carboxyl terminus, it was reported that dispartame Asp-ACC-OMe had a distinct sweet taste [302] and that the corresponding n-propyl ester had 250-300 times the sweetness of sucrose [303]. However, replacement of phenylalanine by 2,3-methanophenylalanine gave tasteless analogues of aspartame [293, 304], and some dimethyl-ACC 214 (methanovaline) and tri-methyl-ACC 215 aspartame analogues [Asp-(Me)n-ACC-OMe] have a bitter taste. These taste properties, which depend on the number and position of the methyl substituents, have been explained on the basis of topochemical models thus, a L-shaped conformation of the dipeptide is necessary for sweet taste, Eq. (86) [3051. 

The following is review on the molecular and physical properties of this class of monooxygenases, which are also known as hydroxylases. A typical monooxygenase reaction is the hydroxylation of an alkane to an alcohol which involves a reduced cosubstrate that reduces a second atom within the O2 molecule to form water. Flavin-containing monooxygenases include lysine oxygenase and 4-hydroxybenzoate hydroxylase. Reduced pteri-dines are involved in the phenylalanine hydroxylase and tryptophan hydroxylase reactions. See also Cytochrome P-450... 

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