Tyrosine tyr

In addition, eNOS is subject to protein phosphorylation. It can be phosphotylated on several serine (Ser), threonine (Thr), and tyrosine (Tyr) residues however, major changes in enzyme function have been reported for the phosphorylation of amino acid residues Seri 177 and Thr495 (in the human eNOS sequence) (Fig. 3). 

It appears as if an axiom of stereochemistry, the absolute identity of the most important chemical and physical properties of chiral isomers, is no longer valid. Experiments using the amino acid tyrosine (Tyr) showed unexpected differences in the solubility of D-and L-Tyr in water a supersaturated solution of 10 mM L-Tyr crystallised much more slowly than that of D-Tyr under the same conditions. The saturated solution of L-Tyr was more concentrated than that of D-Tyr. Supersaturated solutions of DL-Tyr in water formed precipitates containing mainly D-Tyr and DL-Tyr, so that there was an excess of L-Tyr in the saturated solution. The experiments were carried out with extremely great care in order to exclude the possibility of contamination. Further experiments will show whether this is a particular property of tyrosine, or whether other amino acids will show similar behaviour. Possible... 

A catalytically inactive, (tyrosinato)Cu(II)-containing form of GO (pH 4.5 acetate buffer) has been characterized by X-ray crystallography (119, 120) at 1.7-A resolution. Fig. 6 shows the active site. The Cu(II) ion is in a distorted square-based pyramidal environment of a tyrosine (Tyr 495) ligand in the apical position where it is probably bound in its protonated phenol form, a second (modified) tyrosinate (Tyr 272) as well as two histidines (His 496, His 581) in equatorial positions. The fifth coordination site is occupied by a buffer derived acetate that in the active en-... 

Tyrosine Tyr Y 2-Amino-3-(4-hydroxyphenyl)propanoic acid HO- CH2-CHlNH2)-COOH... 

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. 

Aryl side chain containing L-a-amino acids, such as phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), are derived through the shikimate pathway. The enzymatic transformation of phosphoenolpyr-uvate (PEP) and erythro-4-phosphate, through a series of reactions, yields shikimate (Scheme 2). Although shikimate is an important biosynthetic intermediate for a number of secondary metabolites, this chapter only describes the conversion of shikimate to amino acids containing aryl side chains. In the second part of the biosynthesis, shikimate is converted into chorismate by the addition of PEP to the hydroxyl group at the C5 position. Chorismate is then transformed into prephenate by the enzyme chorismate mutase (Scheme 3). 

Tyrosine (Tyr or Y) (4-hydroxyphenylalanine ((5)-2-amino-3-(4-hydroxyphenyl)-propanoic acid)) is a polar, neutral, aromatic amino acid with the formula H00CCH(NH2)CH2C6H50H and is the precursor of thyroxin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and the pigment melanin. Being the precursor amino acid for the thyroid gland hormone thyroxin, a defect in this may result in hypothyroidism. Tyr is extremely soluble in water, a property that has proven useful in isolating this amino acid from protein hydrolysates. The occurrence of tyrosine- 0-sulfate as a constituent of human urine and fibrinogen has been reported. ... 

Figure 1. Contemporary scheme of morphine. Friedrich Sertiirner, who first isolated this alkaloid in an impure form in 1805, did know that it was converted from the pathway of tyrosine, Tyr. The correct morphine structure was determined by Gulland and Robinson in 1923. Moreover, even 200 years after Sertiirner s isolation, scientists are still discussing the synthesis of this alkaloid from a molecular point of view. This is a good example of the scientific evolution of knowledge of alkaloids.

The carbon skeletons of isoleucine (He), phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) are both glucogenic and ketogenic. 

Figure 9-3. Fates of the carbon skeletons upon metabolism of the amino acids. Points of entry at various steps of the tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis are shown for the carbons skeletons of the amino acids. Note the multiple fates of the glucogenic amino acids glycine (Gly), serine (Ser), and threonine (Thr) as well as the combined glucogenic and ketogenic amino acids phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr). Ala, alanine Cys, cysteine lie, isoleucine Leu, leucine Lys, lysine Asn, asparagine Asp, aspartate Arg, arginine His, histidine Glu, glutamate Gin, glutamine Pro, proline Val, valine Met, methionine.

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