Impact of pH? Change in Binding Affinity of protein-ligand complex based on pH and Kd?


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> When the $\mathrm{pH}$ was $5.0$, the temperature was $\pu{25 °C}$,the $K\_\mathrm{D}$ was $\pu{5 μM}$, and [L] was equal to $K\_D$, the protein(s) were half bound. 
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Question considers half bound condition where $[L]= 𝐾\_𝐷$ 



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> If $K\_\mathrm{D} = \pu{20 μM}$ and $\mathrm{pH} = 6.5$, what is the impact on binding affinity? 
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I understand that $K\_\mathrm{D}$ is the inverse of $K\_\mathrm{a}$ and that $K\_\mathrm{D}$ describes the degree of dissociation at equilibrium for the reaction, thus a low $K\_\mathrm{D}$ corresponds to a high binding affinity complex. 


**I don't understand how to account for $\mathrm{pH}$ change though.**


