Final answer:
Gel-filtration chromatography is the most suitable method to determine whether a protein exists as a monomer or in a complex, as it separates proteins based on size and can indicate their oligomeric state in solution.
Step-by-step explanation:
The most suitable method to assess whether a protein exists as a monomer or in a complex is gel-filtration chromatography. This technique, also known as size-exclusion chromatography, separates proteins based on their size and allows researchers to determine the molecular weight and oligomeric state of a protein in solution. Proteins larger than the exclusion limit of the gel beads are eluted first, while smaller proteins elute later, allowing for size-dependent separation.
Gel electrophoresis, while useful in many applications, primarily separates proteins based on their charge-to-mass ratio and is often used in conjunction with SDS to denature proteins and evaluate their molecular weight in a denatured state. Thus, it may not accurately represent the native oligomeric state of proteins. Western blot analysis is a technique for detecting specific proteins with antibodies after electrophoresis, but it also does not usually inform about oligomeric state. ion-exchange chromatography separates based on charge and is not the best choice for oligomerization studies.