Lysine isoelectric point, calculation

H. Neutral lysine can be written HL. The other forms of lysine are H3L2, H2L+, and L. The isoelectric point is the pH at which the average charge of lysine is 0. Therefore, at the isoelectric point, 2[H3L2+] + [H2L+] = [L-]. Use this condition to calculate the isoelectric pH of lysine. 

Calculate the isoelectric point for the following polyftmctional amino acids (a) histidine, (b) lysine, and (c) aspartic acid. (See Table 5-1.)... 

Calculate the isoelectric point (pJ) and the pH at which the maximum total number of charges are present (pH ) for (a) glycine, (b) aspartic acid, and (c) lysine. 

The permeability coefficients of 20 amino acids at physiological pH (7.4) and at the pH of the isoelectric point were taken without alteration from Table 2. Based on pAT values calculated by SPARC and the pH reported in this article, we calculated that the ionic condition of the amino acids was zwitterionic for all but four measurements. The exceptions were aspartic acid at pH 7.4 and glutamic acid at pH 7.4 (which were both net anionic) and lysine at pH 7.4 and arginine at pH 7.4 (which were both net positive). 

Svensson (2) has calculated the conductivities of several ampholytes of low molecular weight. We refer the reader to his works. For example, histidine has pi = 7.81, pi — pK+ = 1.50, and conductivity 3C = 158 mhos cm 10 . At this pH, the contribution from the conductivity of the water is zero. Another example is lysine, with pi = 9.96, pi — pK+ = 0.79 and 3C(corr) = 2.162 mhos cm 10 . Thus lysine has a considerably larger conductivity at its isoelectric point than histidine. This results... 

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