Practical Protein Chemistry - A. Darbre 1989

Determination of the composition of protein oligomers. Preparation of monomers and polypeptide chains
Stoichiometric ratio of monomers in the oligomer

A number of Methods are used to determine the stoichiometric composition of monomers in Oligomeric Proteins. The choice of analytical method depends on both the compositional Features of the oligomer and the technical capabilities of the researcher. Given the labor-intensive nature of many methods and the insufficient reliability of the results thus obtained, data from various approaches should be compared when analyzing oligomer composition. The ratio of monomers is frequently calculated based on the molecular weights of the intact oligomer and its constituent monomers. The modification of subunits using bifunctional cross-linking Reagents is gaining increasingly widespread application. To obtain hybrid oligomers, which are subsequently analyzed by PAGE, monomer Condensation is carried out using monomers isolated from other biological species or chemically modified beforehand. The Use of such artificial techniques as the generation of hybrid oligomers and monomer cross-linking is generally restricted to small oligomers comprising a few subunits. To study oligomers consisting of Different types of subunits, researchers employ dissociation followed by PAGE analysis, densitometry of Coomassie-stained proteins, and incorporation of a radioactive label. Once the molecular weights of the oligomer and monomers have been estimated, calculating the absolute number of subunits is straightforward. Amino acid analysis can also be used to determine the monomer ratio.

Since errors in determining the molecular weights of Proteins can be significant, the obtained data should be evaluated with a degree of caution. The Symmetry of the oligomer molecule is of major importance. Dimeric and tetrameric structures are the most common, though there are numerous Examples of hexamers, octamers, and dodecamers. Only a few studies are known to report the existence of trimers, pentamers, and heptamers [63]. Thus, if calculations indicate that an oligomer comprises eleven monomers, one is most likely dealing with an artifact. The Structure of large oligomers is determined using X-ray crystallography and Electron Cell/15.html">Microscopy [13, 131].