Alanine ionizing groups

Certain amino acids also possess side chains with ionizable groups. For example, the side chain of lysine possesses an ionizable amino group. Because of their structures, alanine, lysine, and the other amino acids can act as effective... 

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Crosslinking of protein monolayers by mercuric ion (MacRitchie, 1970) and silicic acid (Minones et al., 1973) has been reported. These studies are relevant to poisoning by heavy-metal ions and to silicosis, effects that seem likely to result from attack on the cell membrane proteins. Crosslinking by mercuric ion was detected by a spectacular increase in surface viscosity and a decrease in compressibility when a number of proteins (BSA, insulin, ovalbumin, and hemoglobin) were spread on 0.001 M mercuric chloride solution. Poly-DL-alanine was unaffected whereas poly-L-lysine and poly-L-glutamic acid were affected in a similar manner to the proteins, indicating that mercuric ion interacts with the ionizable carboxyl and amino groups on the protein side—chains. Silicic acid similarly caused protein monolayers... 

The answer is b. (klurray, pp 27-36. Scriver, pp 3-45. Sack, pp 1-3. Wilson, pp 101-120.1 Except for terminal amino acids, all a-amino groups and all a-carboxyl groups are utilized in peptide bonds. Thus only amino acids with side chains may be considered. Of these, 7 of the 20 common amino acids have easily ionizable side chains. These arc the basic amino acids lysine, arginine, and histidine the acidic amino acids aspartate and glutamate and tyrosine and cysteine. Leucine, valine, and alanine have hydrocarbon side chains. 

Refer to Table 5.2 for the p fa values for lysine and aspartic acid, both of which have ionizable side chains. Lysine also contains a terminal a-amino and alanine a terminal a-carboxyl group. These values are as follows ... 

The next example of comparatively simplicity, this time nonaqueous, is the crystalline alanine. There are several products of irradiation of that solid crystalline amino acid. In this state it occurs as zwitterion as NMR shows, i.e. the amine group is protonated -N+H3. Single ionization spurs, of a low energy, cause deamination which leads to detachment of ammonia and formation of a free radical. Pulse radiolysis of single crystals of L-alanine shows, that the alanine derived radical CH3-C H-C02-, which shows the spectrum with maximum at 348 nm [9], stabilizes during 5 milliseconds [10], It is usually observed not spectroscopically but by the EPR method [11] it shows extreme stability, being applied as reference dosimeter. 

Chapman and Morrison (1966) have found NMR evidence favoring a dipolar ionic form for the phosphatidyl ethanolamines. Also, their infrared spectra of chloroform solutions favor a dipolar ionic structure. The evidence was as follows if dioleoyl-phosphatidyl ethanolamines exist in chloroform in a nonionic form, then intense bands in the 3300 cm region should occur because of NH stretching frequencies. Bands were found at 3058, 2710, 2538, and a probable band at 3021 cm , which they correlated with vibrations of an NHj group. A comparison of the spectra of dioleoyl-phosphatidyl ethanolamine and a dipolar ionic amino acid, such as alanine, showed almost identical spectra in the 4000 to 2000 cm region. The spectrum of the non-ionized compound, OL-a-alanine methyl ester in chloroform shows intense absorption in the 3300 cm region characteristic of a free primary amino group. 

Ionization constants have been determined for D2O solutions of glycine, gkycylglycine, and DL-alanine (Orlov et al, 1967). The constants were calculated from the peak intensities and were found to be 2.7 and 10.0 for glycine 3.5 and 8.5 for glycylglycine and 2.6 and 10.4 for DL-alanine, for the amino and carboxyl groups, respectively. 

Hidaka et al. [77] reported that amphoteric Af-(2-hydroxyethyl)- -(2-hydroxyalkyl)-P-alanines s cmc values greatly depend on the nature of the electrolytes added to its nearly neutral aqueous solution, and that the cmc value decreased in the following order NaCl > CaClj > Na2S04. Also, their calcium stability is superior to that of A-dodecyl-P-alanines. The effect of pH on this amphoteric amino acid surfactant was smdied in the presence of 0.1 M NaCl [78] and the results showed that the cmc value increased on the acidic side below the isoelectric point pi = 6.8 and remained almost unchanged on the alkaline side. Examination of the configuration with molecular models indicates that the cationic ionization of the amino group on the acidic side probably takes place within the micelle, whereas under alkaline circumstances the anionic ionization of the carbonyl group occurs on the micellar surface. This makes the electrostatic potential for ionization different on the acidic and alkaline sides. 

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