Tyrosine bound

Figure 7-3. Two-dimensional representation of a dipeptide substrate, glycyl-tyrosine, bound within the active site of carboxypeptidase A.

Fig. 90. (A) Glycine-tyrosine bound to carboxypeptidase (443). Indirect attack of Glu-270 promotes the attack of a water molecule on the amido carbonyl group polarized by interaction with zinc. (B) Direct attack of Glu-270 on the amido carbonyl with formation of an anhydride.

Recognition of an adenylylated amino acid by the proper synthase. Shown is adenyl tyrosine bound to the tyrosyl synthase. A network of H bonds not only stabilizes the reaction but also serves to discriminate between different amino acid residues. MC designates main chain (backbone) carbonyl or amino groups participating in hydrogen bonding. 

Tyrosine-bound manganese purple manganese acid phosphatase and ribonucleotide reductase 587... 

Fk 10. Optical difference spectra for the binding of AF to transferrin (14 /cM 25 mM HCO i 100 mM Tris-HCl pH 7.4 25°C). Increasing amounts of AlK(SO)Ll cause the observed spectral changes as a result of the formation of tyrosinate-bound A1 within transferrin. 

When it attacks proteins, pepsin liberates tyrosine bound by central bonds at the carboxyl end of the peptide chain, as well as tyrosine at the amino terminal end. At the Rockefeller Institute, M. L. Anson and A. E. Mirsky made liberation of tyrosine the basis of their method for estimating pepsin. They added a pepsin solution to a standard solution of hemoglobin in 0.6 N HCl. Hemoglobin is a substrate easily prepared in large quantities it can be stored without deterioration and it is uniform from one batch to another. The acidity chosen by Anson and Mirsky is well on the acid side of the pH where small variations in pH cause large changes in peptic activity. Anson and Mirsky stopped the reaction with trichloracetic acid and measured the tyrosine in the filtrate by means of the Ciocalteu-Folin phenol reagent. The method was universally adopted. ... 

The first studies of a synthetic system with a tyrosine bound to a [Ru(bpy)3] photosensitiser were performed in water, in the presence of methyl viologen as an electron acceptor.Irradiation of the complex... 

Thyroid Hormones. Iodine, absorbed as P, is oxidized in the thyroid and bound to a thyroglobulin. The resultant glycoprotein, mol wt 670,000, contains 120 tyrosine residues of which ca two-thirds are available for binding iodine in several ways. Proteolysis introduces the active hormones 3,5,3 -triiodothyronine (T ) and 3,5,3, 5 -tetraiodothyronine (T, (thyroxine) in the ratio Ty.T of 4 1 (121,122). 

Figure 4.16 A schematic view of the active site of tyrosyl-tRNA synthetase. Tyrosyl adenylate, the product of the first reaction catalyzed by the enzyme, is bound to two loop regions residues 38-47, which form the loop after p strand 2, and residues 190-193, which form the loop after P strand 5. The tyrosine and adenylate moieties are bound on opposite sides of the P sheet outside the catboxy ends of P strands 2 and 5.

Figure 4.17 Schematic diagram of bound tyrosine to tyrosyl-tRNA synthetase. Colored regions correspond to van der Waals radii of atoms within a layer of the structure through the tyrosine ring. Red is bound tyrosine green is the end of P strand 2 and the beginning of the following loop region yellow is the loop region 189-192 and brown is part of the a helix in loop region 173-177.

Figure 13.26 Schematic diagram of the SH2 domain from the Src tyrosine kinase with bound peptide. The SH2 domain (blue) comprises a central p sheet surrounded by two a helices. Three positively charged residues (green) are involved in binding the phosphotyrosine moiety of the bound peptide (red). (Adapted from G. Waksman et al.. Cell 72 779-790, 1993.)...

Figure 13.30 Ribbon diagram of the structure of Src tyrosine kinase. The structure is divided in three units starting from the N-terminus an SH3 domain (green), an SH2 domain (blue), and a tyrosine kinase (orange) that is divided into two domains and has the same fold as the cyclin dependent kinase described in Chapter 6 (see Figure 6.16a). The linker region (red) between SH2 and the kinase is bound to SH3 in a polyproline helical conformation. A tyrosine residue in the carboxy tail of the kinase is phosphorylated and bound to SH2 in its phosphotyrosine-binding site. A disordered part of the activation segment in the kinase is dashed. (Adapted from W. Xu et al.. Nature 385 595-602, 1997.)...

Src tyrosine kinase contains both an SH2 and an SH3 domain linked to a tyrosine kinase unit with a structure similar to other protein kinases. The phosphorylated form of the kinase is inactivated by binding of a phosphoty-rosine in the C-terminal tail to its own SH2 domain. In addition the linker region between the SH2 domain and the kinase is bound in a polyproline II conformation to the SH3 domain. These interactions lock regions of the active site into a nonproductive conformation. Dephosphorylation or mutation of the C-terminal tyrosine abolishes this autoinactivation. 

Scheme 10.8 Biosynthesis of epothilone. Individual PKS domains are represented as circles and individual NRPS domains as hexagons. Acyl carrier proteins (ACPs) and thiola-tion domains (T) are posttranslationally modified by a phos-phopantetheinyl group to which the biosynthetic intermediates are covalently bound throughout the chain assembly. The thioesterase domain (TE) cyclizes the fully assembled carbon chain to give the 16-membered lactone. Following dehydration of Cl 2—Cl 3 to give epothilones C and D, the final step in epothilone biosynthesis is the epoxidation of the C12=C13 double bond by the cytochrome P450 enzyme P450epol<. KS ketosyn-thase KS(Y) active-site tyrosine mutant of KS AT acyltransfer-ase C condensation domain A adenylation domain ...

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