Oligomerization, functional importance

The general assumption that receptor dimerization and oligomerization were important processes only for large polypeptide hormones and growth factors has been tempered with the realization that G-protein-coupled receptors may also function physiologically and pathologically as homo- and hetero-dimers. " ... 

The above discussion indicates that a knowledge of the phase behaviour of individual molecular species of lipid comprising the matrix of the thylakoid membrane of higher plant chloroplasts can be informative of the factors governing the stability of the membrane. Perhaps the most important conclusion is that the presence of non-bilayer forming lipids is not simply required to facilitate the dynamic functions such as membrane fusion etc., but also to play a role in the creation of oligomeric functional complexes of the different membrane proteins. 

Much biochemical evidence shows that many if not all 7TM receptors have a strong tendency to aggregate both with themselves and with other 7TM receptors, as most clearly seen in multiple high-molecular-weight bands on sodium dodecyl sulfate (SDS) gels. These bands are by no means restricted to dimers as, in most cases, several higher order oligomeric structures are observed. This is an important point to consider when the functional correlation of dimer formation is addressed in non-family C receptors. 

Torres, G. E., Cameiro, A., Seamans, K., Fiorentini, C Sweeney, A., Yao, W. D and Caron, M. G. (2002) Oligomerization and trafficking of the human dopamine transporter mutational analysis identifies critical domains important for the functional expression of the transporter. J. Biol. Chem. 278, 2731-2739. 

It is also important to note [13a] that for the generic catalyst, termination has a much lower barrier than insertion. Thus (HN=C(H)-C(H)=NH)NiC3H7+ is not going to be an efficient olefin polymerization catalyst. Rather, 2a, will at best be able to produce small oligomers of ethylene. This is in line with the experimental observation [16] that only bis-imines with bulky substituents are able to function as polymerization catalysts whereas less encumbered systems works as oligomerization catalysts. 

A wide variety of methods has been used in studies of oligomerization reactions. The most important quantitative method is potentiometric measurement of pH as a function of the total metal concentration and of the concentration of the analytical excess of acid or base. Other quantitative methods which are often used are potentiometric determination of metal ion concentration, calorimetry, spectrophotometry, and ion exchange. These, together with a number of other techniques, have recently been discussed thoroughly by Baes (22). 

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