How are quaternary proteins formed?

Quaternary proteins are formed by the association of two or more polypeptide chains or subunits. These subunits come together to form a larger, functional protein complex. The subunits can be identical or different, and they are held together by various non-covalent interactions such as hydrogen bonds, salt bridges, and hydrophobic interactions. The quaternary structure is essential for the function of many proteins, including enzymes, antibodies, and hemoglobin.