Diffusivities large molecular mobility

In many products, the spin-relaxation properties of the components can be different due to molecular sizes, local viscosity and interaction with other molecules. Macromolecules often exhibit rapid FID decay and short T2 relaxation time due to its large molecular weight and reduced rotational dynamics [18]. Mobile water protons, on the other hand, are often found to have long relaxation times due to their small molecular weight and rapid diffusion. As a result, relaxation properties, such as T2, have been used extensively to quantify water/moisture content, fat contents, etc. [20]. For example, oil content in seeds is determined via the spin-echo technique as described according to international standards [64]. 

As has been shown for FPR and other receptors diffusion of a receptor protein may be restricted by interaction with the membrane skeleton [5,50]. On the other hand, interaction of G proteins with cytoskeletal elements has also been demonstrated providing for a means to also control G protein distribution in the plasma membrane (for review see [57]). An intriguing idea explaining distinct membrane distribution of G proteins has been put forward by Rodbell and coworkers who observed polydisperse forms of G proteins caused by polymerization of G subunits in analogy to tubulin [58,59]. Formation of these large molecular complexes would result in restricted mobility of the G proteins and could serve as an explanation for membrane domains in neutrophils that are enriched in G proteins (see above). 

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