Amino acid neutral

Mice immunized intranasally with chimeric PVX particles expressing a six-amino-acid neutralizing epitope from gp 41 of HIV-1 produced high levels of HIV-l-specific IgG and IgA antibodies [50], The anti-H66 IgG titers ranged from 2000 to >30,000. Mice immunized intranasally produced IgA in the serum and in fecal extracts. 

Cowie, G.L., J.I. Hedges, and S.E. Calvert. 1992. Sources and relative reactivities of amino acids, neutral sugars, and lignin in an intermittently anoxic marine environment. Geochimica et Cosmochimica Acta 56 1963-1978. 

Amino acids and some small peptides are absorbed into the enterocytes in the jejnnnm. The transport of amino acids from the lumen into the ceU is an active process, coupled to the transport of Na ions down a concentration gradient. There are at least six carrier systems with different amino acid specificities neutral amino acids (i.e. those with no net charge, e.g. branched-chain amino acids) neutral plus basic amino acids imino acids (proline, hydroxyproline) and glycine basic amino acids (e.g. arginine and lysine) P-amino acids and taurine acidic amino acids (glutamic and aspartic acids). 

Keil, R.G., Tsamakis, E., Giddings, J.C. and Hedges, J.I. (1998) Biochemical distributions (amino acids, neutral sugars, and lignin phenols) among size-classes of modem marine sediments from the Washington coast. Geochim. Cosmochim. Acta 62, 1347-1364. 

Millar AL, Jackson N, Dalton H, Jennings KR, LeviM,Wahren B, Dimmeck N (1998) Rapid analysis of epitope-paratope interactions between HIV-1 and 17 amino-acid neutralizing microantibody by ESI mass spectrometry. Eur J Biochem 258 164-169... 

Figure 28.2 The 20 naturally occurring amino acids Neutral amino acids...

Neutral amino acids Neutral amino acids... 

Cowie, G.L., Hedges, J.I. and Calvert, S.E. (1992) Sources and Relative Reactivities of Amino-Acids, Neutral Sugars, and Lignin in an Intermittently Anoxic Marine Environment. Geochimica et Cosmochimica Acta, 56, 1963-1978. 

Special conditions cr (10 mM) j8-Alanine (pH 4) or histidine (pH 5) Hexanoate (10 mM) Neutral and basic amino acids migrate in the opposite direction than acidic amino acids neutral and basic ones move to cathode... 

An important generalization to remember is that amino and carboxyl groups on all amino acids, neutral, acid, and basic, are close to fully charged at physiological pH (pH 7). 

Formaldehyde Method of Sorensen. — This method, which can serve just as well for determining amino-acids as for determining the degree of hydrolysis of protein material, is based on the following prindple If, to a solution of an amino-acid, neutral from the fact of internal neutralization of the acid COjH by the basic NHa, formaldehyde, likewise neutral, is. added, the latter, reacting on the amino group, removes this basic function and the solution immediately becomes add. For example, in the case of glydn. 

As indicated in Fig. 1 the two-dimensional area is divided into parts for acidic amino acids, neutral amino acids, basic amino acids and amines. This simple rule holds true not only for the protein amino acids but for a large number of nonprotein amino acids. 

QM/EFPl scheme was used for investigating a variety of chemical processes in aqueous environment, including chemical reactions, amino acid neutral/zwitterion equilibrium, solvent effects on properties of a solute such as changes in dipole moment and shifts in vibrational spectrum, and solvatochromic shifts of electronic levels [36, 56, 59-60, 71-79]. Applications of a general QM/EFP scheme were limited so far to studies of electronic excitations and ionization energies in various solvents [56-58]. Extensions of QM/EFP to biological systems have been also developed [80-85]. 

The intrinsic pKa thus represents the pK of the group in the protein with all other titratable amino acids in their neutral state. Finally, the interaction energy, between the sites i and j, is... 

An amino-acid, although insoluble in water (e.g., anthranilic acid), is usually soluble in excess of mineral acid in such a case it is important to make the solution only very slightly acid. This applies also to a mixture of a neutral and a basic substance, from which dil. HCl will extract an amino-acid the solution must then be carefully treated with NaOH to precipitate the amino-acid. 

The above method of preparing a neutral solution of the ammonium salt cannot be applied to extremely weak acids (e.g., some amino-acids), the ammonium salts of which dissociate in boiling aqueous solution. 

Since formaldehyde solutions almost invariably contain formic acid, and amino-acids themselves are seldom exactly neutral, it is very important that both the formaldehyde solution and the glycine solution should before mixing be brought to the same pH (see footnote, p. 509), and for this purpose each solution is first madejWl alkaline to phenolphthalein by means of dilute sodium hydroxide solution. This preliminary neutralisation must not be confused with... 

Glycine itself is almost neutral, and requires very little sodium hydroxide to give a pink colour with phenolphthalein some other amino-acids, e.g., glutamic acid, aspartic acid, etc., are definitely more acidic and consequently require more alkali for this purpose cf. footnote, p. 380). 

Then N-Boc-O-benzylserine is coupled to the free amino group with DCC. This concludes one cycle (N° -deprotection, neutralization, coupling) in solid-phase synthesis. All three steps can be driven to very high total yields (< 99.5%) since excesses of Boc-amino acids and DCC (about fourfold) in CHjClj can be used and since side-reactions which lead to soluble products do not lower the yield of condensation product. One side-reaction in DCC-promoted condensations leads to N-acylated ureas. These products will remain in solution and not reaa with the polymer-bound amine. At the end of the reaction time, the polymer is filtered off and washed. The times consumed for 99% completion of condensation vary from 5 min for small amino acids to several hours for a bulky amino acid, e.g. Boc-Ile, with other bulky amino acids on a resin. A new cycle can begin without any workup problems (R.B. Merrifield, 1969 B.W. Erickson, 1976 M. Bodanszky, 1976). 

Another protecting group of amines is 1-isopropylallyloxycarbonyl, which can be deprotected by decarboxylation and a /3-elimination reaction of the (tt-l-isopropylallyl)palladium intermediate under neutral conditions, generating CO2 and 4-methyl-1,3-pentadiene. The method can be applied to the amino acid 674 and peptides without racemization[437]. 

Acid-Base Properties of Amino Acids with Neutral Side Chains... 

Zaitsevs rule (Section 5 10) When two or more alkenes are capable of being formed by an elimination reaction the one with the more highly substituted double bond (the more sta ble alkene) is the major product Zwitterion (Section 27 3) The form in which neutral amino acids actually exist The ammo group is in its protonated form and the carboxyl group is present as a carboxylate... 

This procedure is restricted mainly to aminodicarboxyhc acids or diaminocarboxyhc acids. In the case of neutral amino acids, the amino group or carboxyl group must be protected, eg, by A/-acylation, esterification, or amidation. This protection of the racemic amino acid and deprotection of the separated enantiomers add stages to the overall process. Furthermore, this procedure requires a stoichiometric quantity of the resolving agent, which is then difficult to recover efficiendy. Practical examples of resolution by this method have been pubUshed (50,51). 

Formation of Schiff-Bases. Reaction of an amino acid and an aldehyde oi ketone gives a Schiff-base in neutral or alkaline solution, and following reduction gives the corresponding Ai-alkylamino acid. 

The enzymatic hydrolysates of milk casein and soy protein sometimes have a strong bitter taste. The bitter taste is frequently developed by pepsin [9001 -75-6] chymotrypsin [9004-07-3] and some neutral proteases and accounted for by the existence of peptides that have a hydrophobic amino acid in the carboxyhc terminal (226). The relation between bitter taste and amino acid constitution has been discussed (227). 

---