Tyrosine dissociation constant

The consensus sequences of the ligands interacting with SH2, PTB and SH3 domains are listed with their dissociation constants. Both SH2 and PTB domains bind to phosphotyrosine in a sequence-specific manner. Tyrosine dephosphorylation can reduce the affinity of the SH2 domain to its ligand by 1,000-fold. R, R2 and R3 represent variable amino acids depending on the specific SH2 domain involved. X represents any amino acid. 0 represents a hydrophobic amino acid pY, phosphotyrosine. 

Chromophoric acyl group,4,5 The spectrum of the furylacryloyl group depends on the polarity of the surrounding medium, and also on the nature of the moiety to which it is attached. The spectrum of furylacryloyl-L-tyrosine ethyl ester changes slightly when it is bound to chymotrypsin. There are also further changes on formation of the acylenzyme and on the subsequent hydrolysis. The rate constants for acylation and deacylation and the dissociation constant of the Michaelis complex may be measured by the appropriate experiments. 

Figure 5.4. Schematic representation of the hybrid QSPR-PD model for corticosteroid action on tyrosine aminotransferase (TAT) induction in rat hepatocytes. In this model, the free intracellular concentration is a constant fraction (a) of the plasma concentration, Bmax is the total amount of glucocorticoid receptor (GR), and Kq is an equilibrium dissociation constant.17...

A general method for estimating dissociation values, given a set of solubility and pH measurements for tyrosine and 2,8-dihydroxyadenine, is presented. Equations are derived extending solubility, pH and dissociation constant relationships from weak acids and bases to polyprotic, amphoteric compounds. Included in ttie estimation procedure is a subroutine for approximating ttiermodynamic dissociation constants."... 

Table 1 Acid Dissociation constants of Tyrosine - Containing Peptides"...

Table 2 Microscopic Acid Dissociation Constants and Tautomeric Constants of Tyrosine Peptides...

Figure 8.6 Titration of ligands SB202190 (reference ligand) and VX-745 with tyrosine p38a using an internal standardized titration model. Dissociation constants obtained for nominal and adjusted active protein concentrations are shown bracketed by model curves representing hypothetical stronger l

In this latter case the Michaelis constant can be considerably smaller than the dissociation constant for the enzyme substrate complex, k2jkx2- The Michaelis constant defines the substrate concentration when half the enzyme, in the steady state, is in the form preceding the rate limiting step. Of course the situation can be less well defined when there are several steps with similar rates These comments are intended to underline the warning that Michaelis constants should not be used as measures for substrate affinities. A good example is the comparison of the values for the chymotrypsin catalysed hydrolysis of acetyl-L-tyrosine ethyl ester and the analogous amide. A hundredfold decrease in 23 results in an equivalent increase in... 

A favorable example is given in Figure 4.7. The dissociation rate constant of tyrosine from its complex with tyrosyl-tRNA synthetase is low, so the association and dissociation rate constants can be measured by stopped flow. (Note that sometimes a two-step process may appear to be a single-step reaction see section 6). 

Dissociation of the aldehyde product would leave a low-coordinate, Cu(I) redox center associated with two protonated tyrosine phenols in the active site. This complex is known to be very reactive toward dioxygen, the second-order kinetic constant for reoxidation of the reduced enzyme by O2 being nearly 8x10 s (Borman et aL, 1997 Whit-... 

The micro-constants of enkephalin and tyrosine peptides... were determined according to tiie modified metiiod of complementary tri-stimulus colorimetry (CTS method) (Flaschka H, Applications of complementary tri-stimulus colorimetr). -1. Analysis of binary and ternary colorant systems, Talanta, 7, 90-106 (1960). The acid dissociation and micro-constants thus determined are summarized in Table 1 and Table 2. 

Tryptophan administration to rats results in the stabilization of a number of enzymes for which tryptophan is not a substrate. These include tyrosine aminotransferase (Cihak et al., 1973), phosphoenolpy-ruvate carboxykinase (Ballard and Hopgood, 1973), threonine dehydratase (Peraino et al., 1965), and ornithine aminotransferase (Chee and Swick, 1976). With these enzymes, the decreased lability cannot be shown in vitro, so it is doubtful whether tryptophan itself is the active compound. Perhaps a tryptophan metabolite either binds to the enzymes or affects the dissociation of substrates or cofactors. This latter possibility could be important in the case of the aminotransferases, which have pyridoxal phosphate cofactors, since Litwack and Rosen-field (1973) demonstrated a correlation between the degradation rate constants of a number of enzymes and the rate of coenz)nne dissociation from the molecules. 

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