Redox Potential of a Soybean Ferric Leghemoglobin Reductase

  • Kim, Hyun-Mi (Department of Biochemistry, Natural Science Research Institute, Yonsei University)
  • Received : 1998.05.06
  • Accepted : 1998.06.03
  • Published : 1998.09.30

Abstract

The visible spectra of soybean ferric leghemoglobin reductase exhibited a charge transfer band at 530 nm under aerobic condition. Spectra of the oxidized enzyme show a flavin peak at 454 nm and the enzyme has three redox states associated with the active site of the enzyme. The enzyme has an active disulfide bridge and two-electron transfer may dominate in the ferric state of leghemoglobin reduction. The midpoint potentials of the enzyme were determined by spectrotitration to be -0.294 V for disulfide/dithiol and -0.318 V for FAD/$FADH_2$. Since the midpoint potentials for $NAD^+$/NADH and the ferrous/ferric states of leghemoglobin are -0.32 V and +0.22 V, respectively, it is proposed that two electrons are transferred sequentially from NADH to FAD, to the disulfide group, and then to the ferric state of leghemoglobin in the enzyme reaction.

Keywords

Electron potential;Flavoprotein;Leghemoglobin;Oxidoreductase;Spectrotitration