Abstract
Beef heart aconitase has been studied by low temperature magnetic circular dichroism (MCD) spectroscopy in the wavelength region 300 to 1900 nm. Together with parallel electron paramagnetic resonance and activity measurements, these data enable correlations between Fe-S cluster-type and enzymic activity in aconitase. In samples not exposed to extraneous Fe, the Fe-S cluster in aconitase exhibits the characteristic properties of a 3Fe center in both the as isolated and dithionite-reduced states. On the basis of the detailed form of the low temperature MCD spectra, three types of 3Fe center can be distinguished in biological samples. These are typified by the 3Fe centers in aconitase, Desulfovibrio gigas FdII, and Azotobacter crooccocum Fd. In aconitase, maximal enzymic activity is found to be associated with the build-up of [4Fe-4S]2+ clusters in good agreement with the Mössbauer studies of Kent et al. (Kent, T. A., Dreyer, J. L., Kennedy, M. C., Huynh, B. H., Emptage, M. H., Beinert, H., and Münck, E. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 1096-1100). However, significant catalytic activity (approximately 60%) was obtained by reduction of the 3Fe center with dithionite in the absence of added Fe. The form and intensity of the resultant MCD spectrum are consistent with the majority of the Fe being in the form of reduced 3Fe clusters. The possibility that a reduced 3Fe cluster is capable of promoting partial catalytic activity in aconitase is discussed in light of these results.
Highlights
Beef heart aconitase has been studied by lowtemperature magnetic circular dichroism (MCD) spectroscopy in the wavelength region 300 to I900 nm
The results described above further illustrate the potential of low temperature MCD spectroscopy for elucidating the cluster-type and electronic ground state properties of proteinbound iron-sulfur clusters
The detailed pattern of electronic transitions revealed in thelow temperature MCD spectra establish three classes of [3Fe-4SI1+centers in good agreement with resonance Raman data [45,46] andconsistent with the available redox potential data
Summary
Vol 259, No 4, Issue of February 25, pp. 2274-2282,1984 Printed in U.S A. While the resonance Raman spectrum of aconitase in its inactive state is different in detail from that exhibited by bacterial 3Fe clusters, the pattern of vibrational modes is again indicative of a [3Fe-4S] center, albeit with slightly modified structural The CD spectra of frozen samples of all and such preparations contained iron anldabile sulfur in the derivatives at 4.2 K bore close resemblance to the published room ratio of 1:1.Mossbauer spectroscopy showed that this prepa- temperature spectra [8] giving no indication of any conformational ration contained a [4Fe-4S] cluster, suggesting that the 3Fe center found after oxidative purification is an artifaocft the isolation procedure. Wherethis has been doneit is so indicated inthe text and table
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
