Dimers allosteric control

Tlie term maxizyme is chosen for the designed ribozymes because they ai c highly active, minimized dimeric ribozymes [minimized, active, X-shaped (functioning as a dimer), intelligent (allosterically controllable) ribozymes... 

Muscle glycogen phosphorylase is a dimer of two identical subunits (842 residues, 97.44 kD). Each subunit contains a pyridoxal phosphate cofactor, covalently linked as a Schiff base to Lys °. Each subunit contains an active site (at the center of the subunit) and an allosteric effector site near the subunit interface (Eigure 15.15). In addition, a regulatory phosphorylation site is located at Ser on each subunit. A glycogen-binding site on each subunit facilitates prior association of glycogen phosphorylase with its substrate and also exerts regulatory control on the enzymatic reaction. 

The mammalian (largely rabbit) muscle enzyme has been the most investigated X-ray structural work favours a GTB fold. It has control, covalent and allosteric, at several levels and these are usually discussed in terms of a modification of the Monod-Wyman-Changeux model, in which the individual polypeptide monomers can adopt either a non-catalytic T ( tense ) state or a catalytic R ( relaxed ) state, but mixed oligomers (e.g. TR in a dimer) do not occur. In the extensive structural studies, oligomers with mixed conformations have never been observed. 

---