Question

ESR spin labeling of proteins yields information about all of the following except:

	a.	Polarity of the nitroxide immediate environment
	b.	Distance between the nitroxide and another paramagnetic center in the protein
	c.	Nitroxide side chain mobility
	d.	Solvent accessibility of the nitroxide
	e.	Angle of the nitroxide relative to the backbone peptide bond

Answer 1

e. Angle of the nitroxide relative to the backbone peptide bond cannot be obtained from esr

The analysis of cw ESR spectrum of the SDSL protein provide information about the nitroxide side-chain mobility, the solvent acessibility of side chain, the polarity of its immediate environment and the distance between the nitroxide and another paramagnetic center located in the protein.

The polarity of the immediate surrounding of the nitroxide radical modifies the spin density at N-atom of the nitroxide radical.

If the molecule contains two paramagnetic centers which are rigid and reorient slowly relative to the the electron spin relaxation time of paramagnetic center, the result is an esr signal amplitude which varies in proportion to the inverse of sixth power of the distance between center