Leucine isoelectric point

Leucine (isoelectric point = 6.0) will not migrate. Its structure is... 

The compounds investigated were the amino acids L-isoleucine, L-leucine, L-valine, and L-a-amino butyric acid. These compounds have similar molecular structures, as shown in Figure 2, and will be referred to throughout the present work as L-Ile, L-Leu, L-Val, and L-a-ABA. Where there is little likelihood of confusion, the designation L- will be omitted. Operations examined included crystallization of He through the addition of hydrochloric acid and through cooling. Under acidic conditions He crystallizes as a hydrochloride salt while in the vicinity of the isoelectric point (pH 5.2) it crystallizes as the neutral zwitterionic... 

You will obtain a titration curve of an amino acid with a neutral side chain such as glycine, alanine, phenylalanine, leucine, or valine. If pH meters are available, you read the pH directly from the instrument after each addition of the base. If a pH meter is not available, you can obtain the pH with the aid of indicator papers. From the titration curve obtained, you can determine the pK values and the isoelectric point. 

What form exists at the isoelectric point of each of the following amino acids (a) valine (b) leucine (c) proline (d) glutamic acid ... 

The ester formed above is heated under reflux for 9 hours with 50 ml. of 48% aqueous hydrobromic acid. The reaction mixture is dissolved in 250 ml. of hot water and allowed to cool overnight. The precipitated benzoic acid is removed by filtration, and the filtrate is evaporated to dryness under reduced pressure. The solid residue is dissolved in 50 ml. of hot water, and the solution is brought to pH 6 (isoelectric point for leucine) with 6 i T ammonium hydroxide solution, after which 200 ml. of 95% ethanol is added. Cooling in the refrigerator for 36 hours allows precipitation of the amino acid. The yield is 6.3 g., or 78%. The product may be recrystallized from a mixture of water and ethanol. 

Table 5 presents the amino acid compositions of a number of apoferritins together with their isoelectric point (taken from the literature) where available. There are a number of features whihc are of quite considerable interest. In the first place, although there are clear cut differences between the proteins of different species, a number of very considerable similarities exist. Thus, for all of the apoferritins for which data is available the content of non-polar amino acids (proline, glycine, alanine, valine, methionine, leucine, isoleucine, phenylalanine and tryptophan) remains constant at about 45%. What is even more remarkable is that the content... 

A leucine-rich aj-glycoprotein (mol. wt. 4.96 x 10 ) in human serum (2.1 mg per 100 ml of serum) appears to consist of a single polypeptide chain and 23% of carbohydrate. Human-plasma otj-SH glycoprotein has been freed from zinc aj-glycoprotein—which possesses a similar molecular weight and a similar isoelectric point—by affinity chromatography on a gel-bound zinc chelate. ... 

Bhushan and Ali [21] used optically pure (-) brucine as a chiral selector they selected oL-amino acids which have isoelectric point below pH 7 and carried out separation on stationary phase where pH was 7.1-7.2 (during preparation of the plates they added the silica gel slurry 0.1 N NaOH). In such a case, amino acids existed as an anion and interacted with the basic brucine. Selectivity of the used system for some amino acids (isoleucine, leucine, and alanine) enantiomers was very high h/ F for D,L-serine was 12 and 50, respectively. 

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