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Structural and spectroscopic characterisation of a heme peroxidase from sorghum

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  • Chukwudi I Nnamchi
  • Gary Parkin
  • Igor Efimov
  • Jaswir Basran
  • Hanna Kwon
  • Dimitri A Svistunenko
  • Jon Agirre
  • Bartholomew N Okolo
  • Anene Moneke
  • Bennett C Nwanguma
  • Peter C E Moody
  • Emma L Raven


Publication details

JournalJournal of Biological Inorganic Chemistry
DateE-pub ahead of print - 14 Dec 2015
DatePublished (current) - Mar 2016
Issue number1
Number of pages8
Pages (from-to)1-8
Early online date14/12/15
Original languageEnglish


A cationic class III peroxidase from Sorghum bicolor was purified to homogeneity. The enzyme contains a high-spin heme, as evidenced by UV-visible spectroscopy and EPR. Steady state oxidation of guaiacol was demonstrated and the enzyme was shown to have higher activity in the presence of calcium ions. A Fe(III)/Fe(II) reduction potential of -266 mV vs NHE was determined. Stopped-flow experiments with H2O2 showed formation of a typical peroxidase Compound I species, which converts to Compound II in the presence of calcium. A crystal structure of the enzyme is reported, the first for a sorghum peroxidase. The structure reveals an active site that is analogous to those for other class I heme peroxidase, and a substrate binding site (assigned as arising from binding of indole-3-acetic acid) at the γ-heme edge. Metal binding sites are observed in the structure on the distal (assigned as a Na(+) ion) and proximal (assigned as a Ca(2+)) sides of the heme, which is consistent with the Ca(2+)-dependence of the steady state and pre-steady state kinetics. It is probably the case that the structural integrity (and, thus, the catalytic activity) of the sorghum enzyme is dependent on metal ion incorporation at these positions.

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