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MÖSSBAUER PARAMETERS OF Fe4+ HEME PROTEINS OF SPIN S = 1
C. Schulz, R. Chiang, P. Debrunner
To cite this version:
C. Schulz, R. Chiang, P. Debrunner. MÖSSBAUER PARAMETERS OF Fe4+ HEME PRO- TEINS OF SPIN S = 1. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-534-C2-536.
�10.1051/jphyscol:19792185�. �jpa-00218562�
JOURNAL DE PHYSIQUE
Colloque C2, supplkment au no 3, Tome
40,mars 1979, page
(22-534MGSSBAUER PARAMETERS OF ~ e HEME PROTEINS OF S P I N ~ + S = 1
C. S c h u l z , R. Chiang and P.G. Debrunner
Departments of Physics and Biochemistry, University of I l l i n o i s a t Vrbana-Champaign, Urbana I L 61801, U.S.A.
R6sumC.- On a mesure d e s s p e c t r e s M b s b a u e r du composd I1 d e l a p d r o x y d a s e d e r a i f o r t (HRP 1 1 ) e t du d e r i v d 5 H202 de l a myoglobine (Mb.H202) e n champ Q l e v 6 e n t r e 4,2K e t 120 K . Une c o n f i g u r a t i o n ( t 2 g ) 4 , F e 4 + , S = 1 a d t 6 suggdrde p o u r c e t Q t a t du f e r . En e f f e t , on r e p r o d u i t l e s donn6es expb- r i m e n t a l e s pour t o u s l e s champs e t toyt@+les temp&ratur$s
$
l l $ i p e + d e l ' h a m i l t o n i e n de s p i n , S = l , H = D ~ $ - s ( s + I ) / ~ + ~ ( s ~ - s $ ~ + 6S.g.H + ( < X + . A - B , ~ ~ H ) . I + I . P . I . , a v e c l e s v a l e u r sD = 3 2 + 2 , 5 K ( 3 5 + 2 , 5 K ) , X = 0 , Al= -19,3 T (-18,7 T), Az = - 6 , 5 T ( - 2 , 5 T ) , AE = l,61?0.01 m / s ( 1 , 4 3 + 0 . 0 1 mm/s), = 0 pour HRP I1 (Mb.H202). Ces p a r a m i t r e s s o n t c o m p a t i b l e s , g r o s s i i r e m e n t , a v e c un m o d i l e 2 champ c r i s t a l l i n a x i a l A = 2290 cm-' e t c o n s t a n t e de c o u p l a g e s i n o r b i t e C = 454 cm-'. Les r Q s u l t a t s M ~ s s b a u e r s u p p o r t e n t donc l ' a t t r i b u t i o n d ' u n Q t a t FeP+,-S = I , au f e r d a n s c e s composds.
A b s t r a c t . - H i g h - f i e l d Mgssbauer s p e c t r a o f h o r s e r a d i s h p e r o x i d a s e compound I1 (HRP 1 1 ) and t h e H202 d e r i v a t i v e o f myoglobin (Mb .H202) w e r e measured between 4 . 2 K and 120 K. A ( t l g ) '
,
F e 4 + , S = I , c o n f i g u r a t i o n h a s been s u g g e s t e d f o r t h i s s t a t e o f t h e heme i r o n . The d a t a c a n i n d e e d be s i m u l a t e d f o r a l l f i e l d s and tem e r a t u r e s by t h e S I + s p i q $ a $ l t o n i a nH m D ~ ~ - s ( s + I ) / ~ + ~ ( s $ - s $ ] + 6 g . 7 . 8 + ( < $ . % h g n ~ ) .I + I . P . I . , w i t h t h e v a l u e s
D = 3 2 f 2 . 5 K (35k2.5 K),X
-
0 , hz -19,3 T ( - 1 8 . 7 T ) , A, = 6 . 5 T (-2.5 T ) , AE = 1.61k0.01 m / s (1.43+0.01 mm/s), = 0 f o r HRP I1 (Mb.Hz02). The l i s t e d p a r a m e t e r s a r e r o u g h l y r e p r o d u c e d bY a
l i g a n d f i e l d model w i t h a n a x i a l p a r a m e t e r A = 2290 cm-' and s p i n - o r b i t c o u p l i n g = 454 cm-
.
The MSssbauer d a t a t h u s s u p p o r t t h e a s s i g n m e n t o f a ~ e ' + , S = 1 s t a t e o f t h e heme i r o n i n t h e s e compounds.
S e v e r a l f e r r i c h e m p r o t e i n s r e a c t w i t h H202 and o t h e r p e r o x i d e s t o form compounds o f h i g h e r o x i d a - t i o n s t a t e / I / . These compounds a r e o f c o n s i d e r a b l e i n t e r e s t b e c a u s e o f t h e u n u s u a l c h a r g e s t a t e , ~ e ' + t h a t h a s b e e n p o s t u l a t e d f o r t h e i r o n / 2 / . I n gene- r a l , oxygen i s assumed t o b e t h e s i x t h , a x i a l l i g a n d o f t h e heme i r o n , and c o n s i d e r a b l e mixing o f t h e i r o n 36 and t h e oxygen o r b i t a l s i s e x p e c t e d a c c o r - d i n g t o m o l e c u l a r o r b i t a l c a l c u l a t i o n s / 3 / . Msss- b a u e r s t u d i e s o f a number o f t h e s e compounds h a v e been r e p o r t e d / 2 , 4 - 7 / , which a r e c o m p a t i b l e w i t h a h i g h l y c o v a l e n t i r o n complex o f f o r m a l c h a r g e s t a t e F e 4 + .
F u r t h e r d e t a i l s a b o u t t h e e l e c t r o n i c ground s t a t e o f t h e i r o n c a n b e d e r i v e d from h i g h - f i e l d ~ G s s b a u e r d a t a , b u t t h e e x p e r i m e n t s r e p o r t e d s o f a r /6,7/
d i f f e r c o n s i d e r a b l y i n t h e i r i n t e r p r e t a t i o n . While a l l a u t h o r s a g r e e o n a n o r b i t a l s i n g l e t , s p i n t r i - p l e t ground s t a t e , S = l , s u b s t a n t i a l l y d i f f e r e n t v a l u e s f o r t h e f i n e s t r u c t u r e D , h and t h e m a g n e t i c h y p e r f i n e t e n s o r
*
A h a v e b e e n r e p o r t e d . The p u r p o s e o f t h i s p a p e r i s t o d e m o n s t r a t e t h a t h i g h - f i e l d measurements o v e r a n e x t e n d e d t e m p e r a t u r e r a n g e a r e needed t o d e t e r m i n e D and A, and t h a t t h e a v a i l a b l e*
d a t a a r e q u i t e i n s e n s i t i v e t o t h e r h o m b i c i t y X . We measured t h e MSssbauer s p e c t r a o f t h e H202 d e r i - v a t i v e s o f h o r s e r a d i s h p e r o x i d a s e (Compound I1 o r HRP 1 1 ) / 4 / and met-myoglobin (Mb.H202) / 5 / i n f i e l d s up t o 5.5 T between 4 . 2 K and 120 K.
The s a m p l e s were e n r i c h e d i n 5 7 ~ e by r e c o n s t i t u t i o n o f t h e a p o p r o t e i n s w i t h 5 7 ~ e - h e r n e .
The z e r o - f i e l d s p e c t r a a g r e e d w i t h p r e v i o u s l y pub- l i s h e d d a t a / 7 / , showing a n i s o m e r s h i f t 6C0.1 mm/s and an a l m o s t t e m p e r a t u r e i n d e p e n d e n t q u a d r u p o l e s p l i t t i n g AEs1.5 mm/s. No m a g n e t i c h y p e r f i n e i n t e r - a c t i o n i s o b s e r v e d , a s i s e x p e c t e d f o r a non- Kramers i o n .
The h i g h - f i e l d s p e c t r a were p a r a r n e t e r i z e d u s i n g t h e s p i n H a m i l t o n i a n H = He + Hn, where ( 1 )
+ C f +
He=D
EZ2-
S ( S + I ) / ~ + X ( S ~ ~ - S ~ ~ ] + B H . ~ . s , S = ] (2)+ +-f + + *+
Hn= (S.A
-
~ , B , H ).1
+ 1.p.1. ( 3 )The o r b i t a l s i n g l e t , s p i n - t r i p l e t ground s t a t e o f t h e F e 4 + ( t Z g ) ' , S= I c o n f i g u r a t i o n i s a c c u r a t e l y d e s c r i b e d by a s p i n H a m i l t o n i a n a s l o n g a s t h e a x i a l c r y s t a l f i e l d s p l i t t i n g A i s l a r g e compared t o t h e s p i n o r b i t c o u p l i n g 5 / B / . P e r t u r b a t i o n
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792185
t h e o r y can be used under t h e s e c o n d i t i o n s t o d e r i v e t h e s p i n Hamiltonian parameters from t h e l i g a n d f i e l d s p l i t t i n g . As w i l l be apparent l a t e r t h e sys- tems s t u d i e d s a t i s f y t h i s c r i t e r i o n . I n a s t r o n g f i e l d t h e s p i n o p e r a t o r S i n * H can be r e p l a c e d by i t s e x p e c t a t i o n values <S> -+ i = 1 , 2 , 3 . The s p i n
i '
f l u c t u a t i o n r a t e is assumed t o be f a s t , and t h e
-+ -+
<S>i a r e r e p l a c e d by t h e i r thermal average <S> T' The h i g h - f i e l d d a t a d i s p l a y e d i n f i g u r e s I and 2 show t h a t the magnetic s p l i t t i n g i s l a r g e s t a t t h e lowest and t h e h i g h e s t temperatures while i t p a s s e s through a minimum n e a r 27 K.
VELOCITY I N HU/S 1
F i g . 1 : Mgssbauer s p e c t r a o ? a f r o z e n s o l u t i o n o f t h e met Mb
-
H 2 0 2 complex i n an a p p l i e d magnetic f i e l d of 4 T p a r a l l e l t o t h e g m a r a y s a t tempera- t u r e s of a ) 7 4 K , b) 4 0 K , c ) 27K, d ) 4.2K. The s o l i d l i n e s a r e f i t s t o t h e d a t a u s i n g t h e parameters given i n Table 1 . The v e l o c i t y s c a l e i s r e l a t i v e t o i r o n metal a t room temperature.The minimum r e s u l t s from p a r t i a l c a n c e l l a t i o n of + ++
t h e e x t e r n a l f i e l d by the i n t e r n a l f i e l d <S>T.A/
(gnBn) a s has been observed p r e v i o u s l y i n Compound ES /6/.
The s o l i d l i n e s i n f i g u r e s 1 and 2 r e p r e s e n t t r i a l - and-error f i t s t o t h e corresponding s p e c t r a u s i n g t h e parameters given i n Table I. These parameters a r e by no means unique. Comparable s i m u l a t i o n s a r e o b t a i n e d f o r any v a l u e of the parameter X, O t h t 1 / 3 by making minor adjustments of t h e h y p e r f i n e t e n s o r
i-+ A. The v a l u e of the a x i a l parameter D , however, i s i n s e n s i t i v e t o the choice of
X.
VELOCITY I N lUU/S 1
Fig. 2 : Miissbauer s p e c t r a of a f r o z e n s o l u t i o n of HRP Compound I1 i n an a p p l i e d magnetic f i e l d of 4 T p a r a l l e l t o t h e d i r e c t i o n of t h e ganma r a y s a t temperatures of a ) 9 0 K , b ) 4 0 K , c ) 26K. Spectrum d) i s i n a magnetic f i e l d of 5.5 T a t a temperature of 4.2K. The s o l i d l i n e s a r e f i t s t o the d a t a using t h e parameters g i v e n i n Table 1 . The v e l o c i t y s c a l e i s r e l a t i v e t o i r o n metal a t room temperature.
a-536
JOURNAL DE PHYSIQUE To r e d u c e t h e number o f a d j u s t a b l e p a r a m e t e r s t h eg - t e n s o r was c a l c u l a t e d from t h e p e r t u r b a t i o n ex- p r e s s i o n s , e q u a t i o n s B1 and B2 o f 181.
T a b l e I.- a s s b a u e r p a r a m e t e r s f o r a x i a l symmetry X = q = 0 . F i g u r e s i n p a r e n t h e s e s a r e e s t i m a t e s of t h e u n c e r t a i n t y i n t h e l a s t s i g n i f i c a n t d i g i t . En- t r i e s w i t h o u t u n c e r t a i n t i e s a r e dependent on t h e v a l u e chosen f o r h .
i-+
Once t h e s p i n H a m i l t o n i a n p a r a m e t e r s D ,
X
and A h a v e b e e n d e t e r m i n e d , t h e y can b e compared w i t h t h e p r e d i c t i o n s of a c r y s t a l f i e l d model. Assuming a x i a l symmetry t h e p a r a m e t e r s o f T a b l e I a r e approx- i m a t e l y c o m p a t i b l e w i t h an a x i a l f i e l d A = 2 2 9 0 c r 1 , a s p i n - o r b i t c o u p l i n gC=
454 cm-', and a c o v a l e n c y f a c t o r a2 = < / C 0 = 0.87.To summarize, o u r r e s u l t s a r e q u i t e c l o s e t o t h o s e r e p o r t e d f o r Compound ES / 6 / b u t d i f f e r c o n s i d e r a - b l y from an e a r l i e r i n t e r p r e t a t i o n of HRP I1 and Mb.H202 171. S p e c i f i c a l l y , we can draw t h e f o l l o w - i n g c o n c l u s i o n s :
1) The s p i n H a m i l t o n i a n , e q u a t i o n s 1-3, w i t h S-I p r o v i d e s an a d e q u a t e p a r a m e t e r i z a t i o n o f a l l o u r d a t a i n t h e f a s t - f l u c t u a t i o n l i m i t .
2 ) The t e m p e r a t u r e dependence o f t h e m a g n e t i c i n - t e r a c t i o n i m p l i e s t h a t t h e ground s t a t e of t h e s p i n t r i p l e t i s non-degenerate and f a r removed (> 30 K)
%
from t h e h i g h e r l e v e l s , i . e . t h e a x i a l f i n e s t r u c - t u r e t e r m D is l a r g e and p o s i t i v e . As a consequence t h e a x i a l p a r a m e t e r A of t h e c r y s t a l - f i e l d model must be l a r g e , A = 2290 cm-', a f a c t t h a t e x p l a i n s t h e s m a l l t e m p e r a t u r e dependence of t h e q u a d r u p o l e s p l i t t i n g and j u s t i f i e s t h e u s e o f a s p i n Hamilto- n i a n .
3) A l l t h e p r e s e n t l y a v a i l a b l e d a t a a r e c o m p a t i b l e w i t h a c r y s t a l f i e l d o f a x i a l symmetry, b u t rhombic d i s t o r t i o n s c a n n o t b e r u l e d o u t .
4) The c r y s t a l f i e l d model 1 8 1 p r e d i c t s t h e c o r r e c t s i g n b u t r o u g h l y t w i c e t h e magnitude of t h e observ-
Acknowledgements
T h i s work was s u p p o r t e d by t h e U.S. P u b l i c H e a l t h S e r v i c e under Grant USPH GM 16406. We t h a n k Dr.T.
P e d e r s o n , Department o f B i o c h e m i s t r y , U n i v e r s i t y o f I l l i n o i s , f o r t h e p r e p a r a t i o n of " ~ e - e n r i c h e d myo- g l o b i n and D r . E. ~ G n c k , F r e s h w a t e r B i o l o g i c a l I n s - t i t u t e , U n i v e r s i t y o f M i n n e s o t a , f o r a s e r i e s of h i g h - f i e l d , v a r i a b l e - t e m p e r a t u r e H6ssbauer measure- ments.
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ed q u a d r u p o l e s p l i t t i n g . M o l e c u l a r o r b i t a l c a l c u - l a t i o n s w i t h a n assumed oxygen l i g a n d , however, p r e d i c t v a l u e s i n f a i r agreement w i t h t h e d a t a .
