Enzyme-monomer complex

The mechanism of enzyme-catalyzed ROP was first proposed by Uyama et al. [54]. Here, the catalyhc site of lipase is the serine residue, which forms a complex with the lactone, leading to the formation of an enzyme-monomer complex (EMC). The rate-determining step in the overall polymerization was believed to be the formation of EMC (also known as an enzyme-activated monomer ). 

Hie NO synthases are enzymes of complex composition (MW ca. 300 kDa) that are active as dimers but can also exist as inactive monomers. Furthermore, the NO synthases of types I and III undergo complex regulation by Ca Vcalmodulin. The following cofactors and substrates are required for reaction of the NO synthase ... 

In be complexes bci complexes of mitochondria and bacteria and b f complexes of chloroplasts), the catalytic domain of the Rieske protein corresponding to the isolated water-soluble fragments that have been crystallized is anchored to the rest of the complex (in particular, cytochrome b) by a long (37 residues in bovine heart bci complex) transmembrane helix acting as a membrane anchor (41, 42). The great length of the transmembrane helix is due to the fact that the helix stretches across the bci complex dimer and that the catalytic domain of the Rieske protein is swapped between the monomers, that is, the transmembrane helix interacts with one monomer and the catalytic domain with the other monomer. The connection between the membrane anchor and the catalytic domain is formed by a 12-residue flexible linker that allows for movement of the catalytic domain during the turnover of the enzyme (Fig. 8a see Section VII). Three different positional states of the catalytic domain of the Rieske protein have been observed in different crystal forms (Fig. 8b) (41, 42) ... 

Figure 21-2. Fatty acid synthase multienzyme complex. The complex is a dimer of two identical polypeptide monomers, 1 and 2, each consisting of seven enzyme activities and the acyl carrier protein (ACP). (Cys— SH, cysteine thiol.) The— SH of the 4 -phosphopantetheine of one monomer is in close proximity to the— SH of the cysteine residue of the ketoacyl synthase of the other monomer, suggesting a "head-to-tail" arrangement of the two monomers. Though each monomer contains all the partial activities of the reaction sequence, the actual functional unit consists of one-half of one monomer interacting with the complementary half of the other. Thus, two acyl chains are produced simultaneously. The sequence of the enzymes in each monomer is based on Wakil.

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