Protein subunit
In
biology, a
protein subunit or
subunit protein is a single
protein molecule that assembles (or "
coassembles") with other protein molecules to form a
multimeric or
oligomeric protein. Many naturally occurring proteins and
enzymes are multimeric. Examples include
hemoglobin, ion channels,
DNA polymerase, nucleosomes and
microtubules. The subunits of a multimeric protein may be identical,
homologous or totally dissimilar and dedicated to disparate tasks. In some protein assemblies one subunit may be referred to as a "regulatory subunit" and another as a "catalytic subunit." An enzyme composed of both regulatory and catalytic subunits when assembled is often referred to as a
holoenzyme.
See also: quaternary structure -- allostery -- cooperativity