Identification and characterization of the enzymatic activity of zeta-crystallin from guinea pig lens. A novel NADPH:quinone oxidoreductase

J Biol Chem. 1992 Jan 5;267(1):96-102.


zeta-Crystallin is a major protein in the lens of certain mammals. In guinea pigs it comprises 10% of the total lens protein, and it has been shown that a mutation in the zeta-crystallin gene is associated with autosomal dominant congenital cataract. As with several other lens crystallins of limited phylogenetic distribution, zeta-crystallin has been characterized as an "enzyme/crystallin" based on its ability to reduce catalytically the electron acceptor 2,6-dichlorophenolindophenol. We report here that certain naturally occurring quinones are good substrates for the enzymatic activity of zeta-crystallin. Among the various quinones tested, the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone were the best substrates whereas menadione, ubiquinone, 9,10-anthraquinone, vitamins K1 and K2 were inactive as substrates. This quinone reductase activity was NADPH specific and exhibited typical Michaelis-Menten kinetics. Activity was sensitive to heat and sulfhydryl reagents but was very stable on freezing. Dicumarol (Ki = 1.3 x 10(-5) M) and nitrofurantoin (Ki = 1.4 x 10(-5) M) inhibited the activity competitively with respect to the electron acceptor, quinone. NADPH protected the enzyme against inactivation caused by heat, N-ethylmaleimide, or H2O2. Electron paramagnetic resonance spectroscopy of the reaction products showed formation of a semiquinone radical. The enzyme activity was associated with O2 consumption, generation of O2- and H2O2, and reduction of ferricytochrome c. These properties indicate that the enzyme acts through a one-electron transfer process. The substrate specificity, reaction characteristics, and physicochemical properties of zeta-crystallin demonstrate that it is an active NADPH:quinone oxidoreductase distinct from quinone reductases described previously.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Catalysis
  • Crystallins / isolation & purification
  • Crystallins / metabolism*
  • Cyclic N-Oxides / metabolism
  • Cytochrome c Group / metabolism
  • Dicumarol / pharmacology
  • Electron Spin Resonance Spectroscopy
  • Guinea Pigs
  • Hydrogen Peroxide / metabolism
  • Kinetics
  • Lens, Crystalline / drug effects
  • Lens, Crystalline / enzymology
  • Lens, Crystalline / metabolism*
  • NADP / metabolism*
  • Naphthoquinones / metabolism
  • Nitrofurantoin / pharmacology
  • Oxygen / metabolism
  • Quinone Reductases / antagonists & inhibitors
  • Quinone Reductases / metabolism*
  • Quinones / metabolism
  • Spin Labels
  • Substrate Specificity


  • Crystallins
  • Cyclic N-Oxides
  • Cytochrome c Group
  • Naphthoquinones
  • Quinones
  • Spin Labels
  • NADP
  • Dicumarol
  • Nitrofurantoin
  • Hydrogen Peroxide
  • Quinone Reductases
  • Oxygen
  • tempol
  • juglone