When a protein is treated with a reducing agent such as 2-mercaptoethanol it becomes denatured. The interactions stabilizing the protein that are most affected and lead to denaturation with reducing agent treatment are

Disulfide linkage/bond

Explanation:

The tertiary and quarternary structure of the protein is stabilized by Disulfide linkage which is formed between two thiol groups in the protein. 2-mercaptoethanol is a reducing agent that breaks this disulfide bond.

A protein becomes denature when it loses its native configuration and becomes inactive. So as 2-mercaptoethanol breaks disulfide bond in protein it looses its native configuration and becomes denatured. 2-mercaptoethanol is used in SDS-PAGE to separate protein subunits. Therefore the correct answer is Disulfide linkage/bond.