As protein subunit, or even short subunit is referred to in structural biology a single protein molecule that assembles with other protein molecules and forms with them a functional protein (specifically protein complex). If it is identical subunits, one speaks of a homomeric in different subunits of a heteromeric protein complex.
Many enzymes, ion channels, receptors, structural proteins and others are oligomeric or multimeric proteins, that is, they are composed of several different subunits. Each said subunit consists of a polypeptide chain, respectively. Since, in multimeric proteins different protein molecules are involved, and each individual protein molecule is a gene encoded on the encoding multimeric proteins, more genes are involved.
- Hemoglobin is a built up of four subunits ( tetrameric ) protein; Hemoglobin is therefore a tetramer. There are two α and two β subunits, therefore hemoglobin is heteromeric.