Hello, when the pH is equal to isoelectric point (pI) of protein, the protein would not move in the gel. So, when we perform the SDS-PAGE, we need high pH for the resolving gel.
Solutions with high or low pH values affect electrostatic charges of basic and acidic amino acids which may cause differences in electric potentials on molecular surfaces of different proteins that should help in separating these proteins by SDS-PAGE electrophoresis or ion-exchange column chromatography.
I believe it is need in order to maintain the SDS effect on proteins, which is to make everything negative-charged, making the molecules migrate to the anode; otherwise the system would not flow properly. In acidic pH, excessive [H+] would protonate what should not be neutralized.
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