ACID-CATALYZED REDUCTION OF FERRYLMYOGLOBIN - PRODUCT DISTRIBUTION AND KINETICS OF AUTOREDUCTION AND REDUCTION BY NADH

被引:47
作者
MIKKELSEN, A
SKIBSTED, LH
机构
[1] ROYAL VET & AGR UNIV, KVL, FOOD RES CTR, DK-1871 FREDERIKSBERG C, DENMARK
[2] ROYAL VET & AGR UNIV, DEPT DAIRY & FOOD SCI, DK-1871 FREDERIKSBERG C, DENMARK
来源
ZEITSCHRIFT FUR LEBENSMITTEL-UNTERSUCHUNG UND-FORSCHUNG | 1995年 / 200卷 / 03期
关键词
D O I
10.1007/BF01190488
中图分类号
TS2 [食品工业];
学科分类号
0832 ;
摘要
The pH dependence of iron(II)/iron(III) product distribution, following reduction of the hypervalent iron in equine ferrylmyoglobin by the protein moiety of the pigment (so-called autoreduction) and by NADH (nicotinamide adenine dinucleotide, reduced) and the rate of reduction was found to depend different on pH. Autoreduction is specific acid catalysed and has a more modest temperature dependence than autoxidation of oxymyoglobin, with the activation parameters Delta H-# = 58.5 +/- 0.4 kJ . mol(-1) and Delta S-# = 2.7 +/- 0.1 J mol(-1). K-1 in 0.16 mol . l(-1) NaCl. The product of autoreduction is the iron(III) pigment metmyoglobin, which is slightly modified in the protein moiety. The reaction has a positive kinetic salt effect from which it is deduced that the reactive centre of ferrylmyoglobin has a charge of +1 in agreement with the structure Fe(IV)=O. Reduction by NADH involves parallel reactions of two pigment forms in acid/base equilibrium with each other with a pK(a) equal to 4.9, both forms yielding metmyoglobin as well as the iron(II) pigment, oxymyoglobin, as products. The protonated form reacts faster than the deprotonated form, and two-electron transfer has greater importance for the protonated form with a limiting Fe(II)/Fe(III) product ratio of 0.6 in acidic solution compared to 0.12 in alkaline solution. A square root dependence of rate on NADH concentration suggests involvement of NAD . radicals with a disproportionation as the termination reaction.
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页码:171 / 177
页数:7
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