Applications of Spin Labeling Method to Biopolymer Systems

3 Applications of Spin Labeling Method to Biopolymer Systems 

The cell membrane is one of the most significant constituents for the life. In general, the cell can absorb required substances and exclude wrong ones through the membrane. In order to understand the mechanism of the peptide transport for example, we have to clarify the structure of the membrane, the fluidity of the lipid chain and the interaction between the chain and the peptide in the membrane. The spin label method is very effective for the characterization of the cell membrane because we can allow for selective spin labeling with nitroxide radicals at particular sites in the lipid chain. The labels can also be selectively bonded at particular molecules such as lipid chains and at peptides. The fluidity of membrane by the spin-labeUng method is reviewed by Toyoshima [17]. 

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In this chapter we present typical applications of the spin labeling method to polymer physics and biopolymer systems. 

Abstract Measurements of temperature dependent ESR spectra of spin labels trapped in the polymer matrices is very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. We can characterize the molecular motion of the particular sites in different region by the ESR method. It is possible to detect the mobility of polymer material at the segment or atomic level. ESR studies help to relate the features of the nanometer scale to macroscopic properties of the polymer materials. We present examples of spin labeling studies in the polymer science to help readers new to the field understand how and for what areas the method is effective. In the first part, we give a simple review of the spin labeling method and present applications in the polymer physics related to relaxation phenomena in various systems. In the second part applications to biopolymer system are introduced to help the clarification of various mechanisms of bio-membranes. 

Similar to SEDOR, but appropriate for isolated pairs of spins is the rotational echo double resonance method, or REDOR. In REDOR, the combined dynamics of the isolated two-spin system and the sample rotation serve to generate echoes at the rotor period. These echoes can be dephased by application of a pulse to one of the coupled partners. The amount of dephasing caused by this additional pulse is a measure of the coupling strength, and hence proximity, of the spins in the pair. This experiment is mostly applied to doubly or multiply labeled samples, for example, biopolymers enriched with and... 

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