Download Model Compounds with Superoxide Dismutase Activity: Iron

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BIOCHEMICAL SOCIETY TRANSACTIONS
Model Compounds with Superoxide Dismutase Activity : Iron Porphyrins
and other Iron Complexes
BARRY HALLIWELL and ROBERT F. PASTERNACK
Department of Biochemistry, University of London King's College,
Strand, London WC2R 2LS, U.K.
The enzyme superoxide dismutase (EC 1.15.1.1) is essential to aerobic life (Fridovich,
1975; Halliwell, 1978). All superoxide dismutases are metalloproteins, containing
manganese, iron or copper and zinc as the prosthetic groups. However, some simple
metal complexes also react with the superoxide radical (02-');
for example, complexes
of Cu(I1) with amino acids (Brigelius et al., 1974) and complexes of Mn(1I) with pyrophosphate (Kono etal., 1976) or with quinolino compounds (Howie et al., 1977). Complexes of Cu(I1) 0 1 Mn(I1) with EDTA do not react with 02-.(Halliwell, 1975).
In contrast, complexes of Fe(I1) or Fe(II1) with EDTA react rapidly with 02-*
(Halliwell, 1975). By competition of Fe(I1)-EDTA with Nitro Blue Tetrazolium for 02-*
generated in a xanthine/xanthine oxidase system at pH 10.1, a rate constant of about
3 x 105~-'*s-' was calculated for the reaction of Fe(l1)-EDTA with 02-'at 20°C.
Complexes of iron(I1) or iron(II1) with diethylenetriaminepenta-acetic acid also react
with 02-.at pH10.1 (k 1 x 105~-'.s-' at 20°C).
Halliwell(l975) reported that haematin reacts with 02-*
at pH 10, but under the conditions used this compound would have been extensively aggregated. 0 2 -is. known to
reduce iron(II1) protoporphyrin IX dimethyl ester in organic solvents (Hill et al., 1974).
Certain protein-porphyrin complexes interact with 02-*
in aqueous solution, including
oxidized cytochrome c ( k 1.1 x 106~vl'.s-'at pH7.2: Koppenol et a/., 1976), horseradish peroxidase (k 1 x 10'-1 x 1 0 9 ~ - ' . s - ' at pH5; Sawada & Yamazaki, 1973),
oxyhaemoglobin and methaemoglobin ( k - 4 x lo3 and
6x 103~-1.s-L
at pH7;
Sutton et al., 1976). However, catalase does not react with 02-'at either pH7.8 or 10.2
(Halliwell, 1973).
As part of an investigation into the relation between the structure of porphyrins and
their reaction with 02-.,
we have studied the properties of various metal-ion complexes
of the water-soluble porphyrin tetrakis-(4-N-methyl)pyridylporphine (Fig. 1). The
spectral and aggregation properties of this compound are well-known (Pasternack eta/.,
1977). The compound itself was found not to react with 02-'in a xanthine/xanthine
oxidase system at pH1O.l, nor did its complexes with Zn(1I) or Cu(l1). The Co(ll1)
derivative of tetrakis-(4-N-methyl)pyridylporphinereacted slowly with O2-., but it
could not be decided if the reaction was catalytic in our system. However, the iron(lI1)
-
--
-
Fig. 1. Structure of tetrakis-(4-N-methyl)pyridyIporphine
iron(IZZ)
1978
577th MEETING, OXFORD
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complex reacted rapidly with 02-.in a catalytic manner. The rate constant for O,-*
dismutation was determined by competition of the iron porphyrin with Nitro Blue
Tetrazolium in a xanthine/xanthine oxidase system at pH 10.1 ;a value of 3 x ~O'M-' .s-'
at 20°C was obtained. The iron porphyrin had no effect on xanthine oxidase activity.
Under our reaction conditions, at least 14 molecules of Oz-' reacted with each molecule
of iron porphyrin. Unless catalase was added to the reaction mixture, the H2O2generated
caused degradation of the iron porphyrin to a product with a much lower Soret intensity,
probably a bile-pigment type of compound. This product also catalysed dismutation of
02-' ( k = 2 X 1o6M-' .S-' ). In the presence of catalase, the Soret band of the iron
porphyrin decreased and broadened slightly on first exposure to xanthine/xanthine
oxidase, but then re-attained its original intensity. This suggests the intermediate formation of some iron(I1) porphyrin. The simplest way of representing the reaction of
tetrakis-(4-N-methyl)pyridylporphineiron( 111) [Fe(III)TMpyP] with 0,-. would be:
Fe(II1)TMpyP +02-'
--> Fe(II)TMpyP+O,
Fe(II)TMpyP+O2-'+2HZ0
Fe(III)TMpyP+H20,+20H-
(1)
(2)
Further investigations on the reaction mechanism and on the effect of complexformation of the porphyrin with proteins are required.
Brigelius, R., Spottl, R., Bors, W., Lengfelder, E., Saran, M. & Weser, U. (1974) FEBS Left.
47, 72-75
Fridovich, 1. (1975) Annu. Rev. Biochem. 44, 147-159
Halliwell, B. (1973) Biochetn. 1.135, 379-381
Halliwell, B. (1975) FEBS Lrft. 56, 34-38
Halliwell, B. (1978) Cell B i d . Int. Rep. 2 , 113-128
Hill, H. A. O . ,Turner, D. R. & Pellizer, G. (1974) Biochem. Biophys. Res. Commun. 56,739-744
Howie, J. K., Morrison, M. K. & Sawyer, D. T. (1977) in E/ecfrochemica/SfuciesofBio/ogica/
Sysferns (Sawyer, D. T., ed.), pp. 97-1 12, American Chemical Society, Washington
Kono, Y., Takahashi, M. & Asada, K. (1976) Arch. Biochem. Biophps. 174, 454-462
Koppenol, W. H., Van Buuren, K . J.
449, 157-168
Pasternack, R. F., Lee, H., Malek, P.
Sawada, Y . & Yamazaki, 1. (1973) Biochim. Biophys. Acfa 327, 257-265
Sutton, H. C., Roberts, P. B. & Winterbourn, C. C. (1976) Biochem. J . 155,
Oxidation of Thiol Compounds by Catalase and Peroxidase in the Presence
of Manganese@) and Phenols
J O H A N D E RYCKER and BARRY HA.LL1WELL
Department of Biochemistry, University of London King's College,
Strand, London WC2R 2LS, U.K.
Catalase breaks down H 2 0 2to O2 and water, but in the presence of H 2 0 2 it can also
act as a peroxidase, oxidizing compounds such as ethanol, formate and nitrite. O n
exposure to acid o r alkaline p H values, the catalatic activity of catalase is decreased,
but the peroxidatic activity is increased (Inada et al., 1961 ; Marklund, 1973). For example, catalase gains the ability to oxidise NADH in the presence of Mn2+and phenols
(Caravca & May, 1964). It also catalyses conversion of 3-hydroxyanthranilate into
cinnabarinate in the presence of MnZ+(Savage & Prinz, 1977).
Breakdown of H 2 0 2 by catalase is inhibited by thiol compounds (Dale & Russell,
1956; Keilin & Nicholls, 1958; Olinescu & Cotae, 1973; Scheifer et af., 1976). We
report here that catalase can bring about oxidation of thiol compounds in the presence
of MnZ+ and certain phenols. Horseradish peroxidase catalyses a similar reaction
(Stonier & Yang, 1973), but its specificity for phenols is different from that of catalase.
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