EPR of whole cells and organelles

Thus far we tacitly assumed that our EPR tubes were filled with pure, or at least to some extent purified, biomolecular preparations. However, what will we find when we try to measure, for example, whole cells In other words, how complex can a sample actually be without us losing track of all the overlaying signals What would be the dynamic range of signal amplitudes that we can resolve from a single sample  

Measuring whole cells, or perhaps purified organelles from whole eukaryotic cells, for example, mitochondria, goes back to the very first days of bioEPR spectroscopy (Beinert and Lee 1961) and has since then over and over again proven to be useful for the particular purpose of studying respiratory chains, that is, the set of redox enzymes that form the heart of the bioenergetic machinery and that, for this 

In the EPR of mammalian cells, we do not see much in addition to the signals from the respiratory complexes. The enzyme aconitase from the citric-acid cycle can be detected, and also the protein cytoplasmic aconitase, later identified as the mRNA translation regulatory factor iron regulatory protein IRP-1, which actually started its career in biochemistry as an EPR signal that could not be assigned to the respiratory chain (Kennedy et al. 1992). 

FIGURE 13.6 Whole bacterial-cell EPR. A frozen concentrated suspension of cells from the sulfate-reducing bacterium Desulfovibrio vulgaris gives an EPR spectrum with only a [2Fe-2S]1+ signal and a flavin radical signal, both from adenosine phosphosulfate reductase. 

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