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