Glutamate titration

The heparin and poly-L-glutamate titrations show a markedly different behavior than do the DNA titrations. As polyanion is added, the fluorescence of the an-thrylpolyamine solution decreases until a well-defined minimum is reached. A new emission at 510 nm, which we assign to the anthracene excimer of 14, increases and decreases coincidently with the titrated fluorescence minimum. Likewise, the UV spectrum of 10 fiM 14 with added heparin shows hypochromism that occurs and disappears coincidently with the fluorescence minimum and a 2-nm red shift. We have proposed template-directed excimer formation as the physical basis for these observations. In the absence of heparin, fluorescence of the unassociated probe is observed. As heparin is added, the fluorescence decreases as a result of heparin-directed interaction between probe molecules. Additional heparin permits the fluorophore population to diffuse over the length of the poly anion, thus avoiding excimer formation and yielding a net CHEF. 

Most frequently, protonation or deprotonation of protein occurs at ionizable, also called titratable, side chains, such as aspartate, glutamate or histidine. The ionization equilibrium of a titratable site,... 

With multiple ionizable groups, such as in amino acids and proteins, each group titrates separately according to its pKa. The titration curves shown in Fig. 23-5 are for the amino acids glycine, histidine, and glutamate. 

Because synthetic products are isolated as the barium or, more frequently, the calcium salt of leucovorin, common acid-base titrations are not reported. If this type of titration or one in which the cation is exchanged were feasible, the results would require careful interpretation because impurities containing the glutamic acid moiety would respond similarly to leucovorin when the carboxyl groups are being analyzed. 

Figure 3.16. Effects on the fluorescence of anthrylpolyamme 14 on titration by four biological polyanions, o—O, Heparin A—A. poly-L-glutamate — , dsDMA a—A, ssDNA. (Reproduced from Ref. 25.

Aspartic acid Glutamic acid HjO Pd"L Pd"L2 potentiometric titration Aspartate chelates are slightly more stable than corresponding glutamate chelates. a... 

FIGURE 3-12 Titration curves for (a) glutamate and (b) histidine. The pKa of the R group is designated here as ptfR. 

A solution containing 0.100 M glutamic acid (the molecule with no net charge) was titrated to its first equivalence point with 0.025 0 M RbOH. 

Brignon et al. (1969) demonstrated that the maximum acid-binding capacity of /3-lactoglobulin D is the same as that of the other variants. The curves are identical at pH 4.0. At pH 6.5, one less proton is dissociated in the titration of the D variant than with the B variant, as would be predicted from the substitution of a glutamine residue for a glutamic acid residue in B. The anomalous carboxyl group observed in the other variants is also detected in the D variant. 

Using the pKa values from problem 3, construct the theoretical titration curve showing the equivalents of H+ or OH reacting with 1 mol of glycine as a function of pH. Note that the shape of this curve is independent of the pfCa. Sketch similar curves for glutamic acid (pK./s equal 2.19,4.25, and 9.67), histidine (pfCa s equal 1.82,6.00, and 9.17) and lysine (pfCa s equal 2.18,8.95, and 10.53). 

Titration curves of glutamic acid, lysine, and histidine. In each case, the pK of the R group is designated pKR. 

Titration curve of /3-lactoglobulin. At very low values of pH (<2) all ionizable groups are protonated. At a pH of about 7.2 (indicated by horizontal bar) 51 groups (mostly the glutamic and aspartic amino acids and some of the histidines) have lost their protons. At pH 12 most of the remaining ionizable groups (mostly lysine and arginine amino acids and some histidines) have lost their protons as well. 

Given the pKa values in the text, predict how the titration curves for glutamic acid and glutamine differ. 

Moreover, high enantioselectivity has been reported for an MIP that was selective for Z-glutamate [33]. Here, changes in the UV-vis absorbance of the l-(4-styryl)-3-(3-nitrophenyl)urea monomer were monitored, as opposed to the previous studies where the intrinsic absorbance of the template was measured. The UV-vis spectroscopy titration of the functional monomer with different concentrations of the template in solution led to a bathochromic shift from 349 to 364 nm. The colour change of both the solution and the resulting bulk polymer upon addition of Z-glutamate was visible even to the naked eye, with a 1 1 monomer-to-template ratio demonstrated. 

FIGURE 2.18 Titration curve of glutamic acid ( pKal = 2.2, pKa2 = 4.3, and pK = 9.4). Thus, in the titration of a diprotic weak acid H2A, Equation (2.150) reduces to ... 

What is the isoelectric point of -y-carboxyglutamate Assume that the pK values of the two y-carboxyl groups are identical at 4.1. Draw a titration curve for y-carboxy glutamate. 

Photometric determinations with p-chloromercuribenzoate (3) were carried out in phosphate at pH 8 27 1SH groups were found per mole of unmodified and also of acetyl glutamate-activated carbamyl-P synthetase. With cold-inactivated enzyme, however, only 19 to 20 groups could be detected. The same results were obtained by amperometric titration in aqueous solution (2) and in 8M urea (5) after sulfitolysis on the cold-inactivated enzyme, an average of 23 SH groups per mole of enzyme was determined. The cases thus far examined, of substrate-induced enzyme inactivation, show also a change in SH group content (1, 14). 

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