Microtubules are composed of tubulin protein dimer subunits. NatE complex consists with subunit Naa50p and two NatA subunits, Naa10p and Naa15p. Glutathione reductase is a dimer that contains two identical subunits. Paclitaxel binds to the beta-tubulin subunits of microtubules. The ribosomal subunits of bacteria and eukaryotes are quite similar. Functional NMDA receptors are heterotetramers composed of two GluN1 and typically two GluN2 subunits. Activin is a dimer composed of two identical or very similar beta subunits. The protein enzyme contains two catalytic subunits and two regulatory subunits. Tyrosine hydroxylase is a tetramer of four identical subunits (homotetramer). Lactate dehydrogenase is composed of four subunits (tetramer). F is a water insoluble protein with eight subunits and a transmembrane ring. NMDA receptors are heterotetramers with two GluN1 subunits and two variable subunits. It consists of several oligomeric structural subunits made of protein called protomers. These are formed from identical protein subunits called capsomeres. These functional roles are contributed by the tails of the histone subunits.