Step 1: Understanding two-dimensional electrophoresis.
Two-dimensional electrophoresis is a technique used to separate proteins based on their isoelectric point (pI) and molecular weight. The first dimension is isoelectric focusing (separation based on pI), and the second dimension is SDS-PAGE (separation based on molecular weight).
Step 2: Analyzing the options.
(1) Separates proteins of identical molecular weight, same pI but different charge: This is incorrect because proteins with the same molecular weight and pI will not be separated based on charge in this method.
(2) Separates proteins of different molecular weight and different pI: This is incorrect because two-dimensional electrophoresis specifically separates proteins based on their pI and molecular weight, not just by these factors independently.
(3) Separates proteins of identical molecular weight that differ in pI: This is incorrect. While the method does separate proteins with different pI, it also accounts for molecular weight, making this statement incomplete.
(4) Isoelectric focusing is also termed as two-dimensional electrophoresis: Correct — Isoelectric focusing, which is the first dimension of two-dimensional electrophoresis, is indeed often referred to in this context.
Step 3: Conclusion.
The correct answer is (4) Isoelectric focusing is also termed as two-dimensional electrophoresis.