J. Biol. Chem., Vol. 261, Issue 20, 9239-9245, 07, 1986
Spectroscopic characterization of the number and type of iron-sulfur clusters in NADH:ubiquinone oxidoreductase
AT Kowal, JE Morningstar, MK Johnson, RR Ramsay and TP Singer
The number and type of iron-sulfur clusters present in the NADH
dehydrogenase of the mammalian respiratory chain were studied by a
combination of low temperature magnetic circular dichroism (MCD) and
quantitative electron paramagnetic resonance spectroscopies. MCD was used
with the high molecular weight, soluble enzyme, and EPR was used with both
the purified enzyme and Complex I (NADH:ubiquinone oxidoreductase). The
results of the EPR experiments of the two types of preparations agreed with
each other, as well as with the data in the literature for various types of
membrane-bound preparations. The two methods gave concordant results
showing the presence of one binuclear and of three tetranuclear
NADH-reducible iron-sulfur clusters. Earlier studies using the cluster
extrusion technique indicated a higher ratio of binuclear to tetranuclear
clusters which may be explained by cluster interconversion during the
extrusion process.