What are the ionic structures of lysine that predominate at the following pH's: 1.0, 6.0, 9.5 and 11.0? Lysine: Mr = 146 pK1 (-COOH) = 2.18 pK2 (-NH+3) = 8.95 pK3 (R group) = 10.53 pI = 9.74...

What are the ionic structures of lysine that predominate at the following pH's: 1.0, 6.0, 9.5 and 11.0?

Lysine:

  • Mr = 146
  • pK1 (-COOH) = 2.18
  • pK2 (-NH+3) = 8.95
  • pK3 (R group) = 10.53
  • pI = 9.74
  • Hydropathy index = -3.9
  • Occurance in proteins (%) = 5.9

Asked on by gemm5

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jerichorayel | College Teacher | (Level 2) Senior Educator

Posted on

Let us first identify the structure of Lysine in order to get its state at a particular pH. Lysine is a basic amino acid. It has an `-NH2` group in its side chain.`HO_2C CH(NH_2)(CH_2)_4NH_2`  

To help us in determining the predominating ions at a particular pH, the pK and pI values are needed. 

At pH = 1.0 which is below pK_1, lysine with both -NH2's that are protonated are predominating. `HO_2C CH(NH_3^+)(CH_2)_4NH_3^+`

At pH = 6.0, which is slightly above the middle point of pk1 and pk2, the predominating species is `^(-)O_2C CH(NH_3^+)(CH_2)_4NH_3^+`

At pH  = 9.5 which is near the pI, the predominating specie is `^(-)O_2C CH(NH_2)(CH_2)_4NH_3^+`

And at pH = 11.0, which is above the pK_3, the predominating specie is `^(-)O_2C CH(NH_2)(CH_2)_4NH_2`

 

Sources:

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