Question

The isoelectric point (pI) for the LDH isoforms are: LDH-A (pI = 8.4) and LDH-B (pI = 5.7).

Under Native PAGE conditions, which protein do you expect to migrate fastest in the gel?

Explain.

Answer 1

Answer: LHD-B

In Native PAGE, the proteins are loaded without denaturing them with SDS. The migration of proteins during electrophoresis occurs towards the positive side.

The running buffer of Native PAGE has a pH of 8.3.

Since LDH-A has pI of 8.4, at the pH of 8.3, LDH-A has a net-positive charge (since pH < pI )

Since LDH-B has pI of 5.7, at the pH of 8.3, LDH-B has a net-negative charge (since pH > pI )

Thus, LDH-B, being negatively charged, will migrate fastest towards the positive side.

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