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IDENTIFICATION OF MEMBRANE BOUND FERREDOXIN-LIKE CENTRES IN PHOTOSYSTEM
I OF BLUE-GREEN ALGAE BY MÖSSBAUER AND EPR SPECTROSCOPY
J. Rush, C. Johnson, E. Evans, M. Evans
To cite this version:
J. Rush, C. Johnson, E. Evans, M. Evans. IDENTIFICATION OF MEMBRANE BOUND
FERREDOXIN-LIKE CENTRES IN PHOTOSYSTEM I OF BLUE-GREEN ALGAE BY MÖSS-
BAUER AND EPR SPECTROSCOPY. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-481-
C1-482. �10.1051/jphyscol:19801189�. �jpa-00219678�
JOURNAL DE PHYSIQUE Colloque C1, supplkment au n O 1, Tome 41, janvier 1980, page C1-481
IDENTIFICATION OF MUvlBRANE BOUND FERREDOXIN-LIKE CENTRES I N PHOTOSYSTEM I OF BLUE-GREEN ALCAE BY mSSBAUER AND EPR SPECT!?OSCOPY
J.D. Rush, C.E. Johnson, E.H. Evans and
+
M.C.W. ~ v a n s ~Department of Physics, LiverpooZ University, LiverpooZ, L69 3BX, EGGAND.
+
BioZogy Division, Preston PoZytechnic, Corporation S t r e e t , Preston, ENGLAND.x Department of Botany and MicrobioZogy, University CoZZege London, Cower S t r e e t , London, WClE 6BT, ENGLAND.
Introduction
Spectroscopic techniques have played an used in the present measurements were purified important part in the study of iron-sulphur membrane fractions and the latter species is proteins (e.g. ferredoxins). These proteins, found to be concentrated in the fraction in which which contain several iron atoms in their active most Photosystem I activity is found 141. Reduc- centres, are non-magnetic (i.e. total net spin tion was achieved with sodium dithionite and the S = 0) when oxidized, and paramagnetic (with S =
4)
reduction was monitored by observation of the epr when reduced. In the reduced state the average g- signals. Reduction was performed so chat signals value determined by epr is less than 2, and the A and B had approximately maximum intensity and K6ssbauer spectra measured at helium temperatures signal X was not present.and in large magnetic fields are very character-
Results istic and show both positive and negative hyperfine
Fig. 1 (a) shows the Miissbauer spectrum of fields indicative of antiferromagnetic spin
Photosystem I in the native (oxidized) state coupling between the iron atoms. Nearly all the
measured in a magnetic field of 6T at 4.2K. The previous work has been done on soluble proteins
spectrum consists of a Zeeman-split quadrupole which can be isolated from their organisms.
doublet with no magnetic hyperfine field .:.e. the In this paper we describe measurements on
membrane fractions containing Photosystem I from blue-green algae. Under various conditions of light induced and chemical reduction three distinct epr signals have been observed with gav < 2
I
Fig. I-
L I-
(A, B and X), / I / and / 2 / . From the MZissbauer
,.>
spectra we have been able to identify ferredoxin- like centres in the membrane.
Previous M8ssbauer measurements on crude
!C i
-
membrane fractions from the blue-green alga Chlorogloea fritschii grown on ~''e have been shown to contain at least two distinct iron
containing species / 3 / : one is paramagnetic and
- -
associated with iron storage or metabolism; the
I I I I I I 1
other in the native state is very similar to the -8.0 4 . 0 -2.0 0.0 2.0 U.0 6.0
vaaIrr wsun non-magnetic centres of Fe-S proteins. The samples
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801189
C1-482 JOURNAL DE PHYSIQUE
active centre is non-magnetic. The chemical shift and quadrupole splitting are very similar to those of known non-magnetic centres of soluble ferre- doxins
.
Fig. 1 (c) shows the spectrum in the reduced state where a large splitting is observed arising from magnetic hyperfine interactions. The spectrum of reduced 4Fe-4s ferredoxin from Bacillus
stearothermophilus /5/ is shown for comparison in Fig. I(b). It can be seen that the Mttssbauer spectrum of the reduced membrane fraction appears to be well described by the sum of two components:
(i) oxidized (similar to Fig. I (a) ) and (ii) reduced (similar to Fig. I(b) ) . Thus A and B can be identified as being due to iron-containing species with properties similar to those of the paramagnetic (total spin ='
4 )
Fe-S centres of soluble f erredoxins.Computer simulations and the experimental spectra of reduced membrane fraction samples at 4.2K in fields of (a) 0.5T and (b) 6T are compared in Fig. 2. The simulations are constructed by the
1 I I I I I I
Fig. 2
superposition of oxidized (non-magnetic) and reduced (~aramagnetic) subspectra. The parameters of the oxidized component ("-') are taken to be those of the quadrupole doublet observed in a 4.2K zero field reduced sample spectrum. The parameters of the reduced components ( . - - - and ----) are taken to be those found for the reduced B-stearothermo- philus ferredoxin /5/; two subspectra are shown for the reduced component as in the model successfully used for the reduced ferredoxin and the calculation is performed as described in that paper. The solid line shows the result of such simulations with a ratio of oxidized to reduced components of I:].
The major features of the experimental spectra are well reproduced by the simulation which therefore provides very strong evidence that the changes in the Photosystem I spectra observed on reduction of centres A and B are due to 2 50% of the iron present being in a very similar chemical form to that of the 4Fe-4s centres of ferredoxins. The remaining iron, whose spectrum is consistent with it being in oxidized Fe-S centres, is unchanged by the present chemical reduction. The question of whether the unchanged component may be responsible for the epr signal X under more strongly-reducing sample preparation conditions is at present under investigation.
References
/ I / Evans M.C.W., Sihra C.K. and Cammack R.
(1976) Bi0chem.J.
158,
71-77/ 2 / Evans E.H., Cammack R. and Evans M.C.W.
(1976) Biochem.Biophys.Res.Commun.
67,
111-114.
/ 3 / Evans E.H., Carr N.G., Rush J.D. and Johnson
C.E. (1977) Bi0chem.J.
166,
547-551./ 4 / Evans E.H., Rush J.D., Johnson C.E. and
Evans M.C.W. (1979) ~iochem.~.
182
(To be published).I I I I I I I
-80 -40 0 0 LO 0.0 /5/ Middleton P., Dickson D.P.E., Johnson C.E.
QELCCITY tmlSEfl and Rush J.D. (1978) Eur.J.Biochem.
88
135-141.
