Protein subunit

In microtubules and other cytoskeloton proteins. 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. One subunit is made of one polypeptide chain. A polypeptide chain has one gene coding for it - meaning that a protein must have one gene for each subunit.