PROBING THE BACKBONE DYNAMICS OF OXIDIZED AND REDUCED RAT MICROSOMAL CYTOCHROME B(5) VIA N-15 ROTATING-FRAME NMR RELAXATION MEASUREMENTS - BIOLOGICAL IMPLICATIONS
L. Banci et al., PROBING THE BACKBONE DYNAMICS OF OXIDIZED AND REDUCED RAT MICROSOMAL CYTOCHROME B(5) VIA N-15 ROTATING-FRAME NMR RELAXATION MEASUREMENTS - BIOLOGICAL IMPLICATIONS, Biochemistry, 37(35), 1998, pp. 12320-12330
Rotating frame N-15 relaxation NMR experiments have been performed to
study the local mobility of the oxidized and reduced forms of rat micr
osomal cytochrome b(5), in the microsecond to millisecond time range.
Measurements of rotating frame relaxation rates (R-1 rho) were perform
ed as a function of the effective magnetic field amplitude by using of
f-resonance radio frequency irradiation. Detailed analysis of the two
data sets resulted in the identification of slow motions along the bac
kbone nitrogens for both oxidation states of the protein. The local mo
bility of reduced and oxidized cytochrome b(5) turned out to be signif
icantly different; 28 backbone nitrogens of the oxidized form were sho
wn to participate in a conformational exchange process, while this num
ber dropped to 12 in the reduced form. The correlation time, tau(ex),
for the exchange processes could be determined for 21 and 9 backbone n
itrogens for oxidized and reduced cytochrome b(5), respectively, with
their values ranging between 70 and 280 mu s. The direct experimental
evidence provided in this study for the larger mobility of the oxidize
d form of the protein is consistent with the different backbone NH sol
vent exchangeability recently documented for the two oxidation states
[Arnesano, F., et al. (1998) Biochemistry 37, 173-184]. Our experiment
al observations may have significant biological implications. The diff
erential local mobility between the two oxidation states is proposed t
o be an important factor controlling the molecular recognition process
es in which cytochrome b(5) is involved.