What does isoelectric focusing determine about a protein?

Isoelectric focusing is a technique used to separate different molecules by the differences in their isoelectric points (pI). The isoelectric point is the pH at which a particular protein carries no net electrical charge. During isoelectric focusing, proteins are placed in a pH gradient and migrate until they reach the point where their net charge is zero. At this point, they stop moving, allowing for the determination of the protein's isoelectric point.

This technique is especially useful in biochemistry for characterizing proteins, as it can reveal information about the protein's overall charge, which is influenced by its amino acid composition and modification. Knowing the pI is critical for various applications, including protein purification, characterization, and understanding protein interactions.

The other options do not accurately describe what isoelectric focusing determines. For example, total protein concentration is assessed through different methods such as spectrophotometry or BCA assays. Molecular weight determination typically involves techniques like SDS-PAGE or mass spectrometry, and amino acid sequencing is performed using methods like Edman degradation or mass spectrometry, not isoelectric focusing.