Premium
Kinetics of the Mammalian Glutaredoxins: GRx2 Is Less Active, But Mimics the Catalytic Mechanism of GRx1
Author(s) -
Gallogly Molly Megan,
Starke David W,
Leonberg Amanda K,
Mieyal John J
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a274-a
Subject(s) - glutaredoxin , glutathione , chemistry , thiol , oxidoreductase , thioredoxin reductase , biochemistry , glutathione reductase , cytosol , thioredoxin , oxidative stress , biophysics , enzyme , biology , glutathione peroxidase
Glutaredoxin (GRx) is a thiol‐disulfide oxidoreductase that utilizes glutathione (GSH) to reduce protein‐glutathione mixed disulfides (protein‐SSG). GRx catalysis serves important roles in redox homeostasis and signal transduction (Shelton et. al., 2005). Mammalian cells have two GRx isoforms: GRx1, primarily in cytosol, and GRx2, primarily in mitochondria (Gladyshev et al., Lundberg et. al., 2001). GRx2 displays <35% sequence identity to GRx1, but it has analogous active site and glutathionyl stabilization motifs. Here we report GRx2 mimics GRx1 remarkably. Like GRx1, GRx2 displays ping‐pong kinetics ‐ the apparent K M and V max values for protein‐SSG and GSH change in proportion to concentration of the other substrate. The active site thiol pK a of GRx2 is 4.5, one pH unit higher than the corresponding pK a for GRx1 (3.5), predicting Grx2 would display 25% of GRx1 activity (Srinivasan et al. 1997). In fact, GRx2 activity is 10% of GRx1, suggesting another change in chemistry of catalysis besides the pKa difference. While GRx2 can couple to thioredoxin reductase (TRase) (Johansson et al . 2004), turnover by TRase is far less efficient than by GSH plus GSSG reductase (GRase), even when GRase and GSH are one‐tenth their typical concentrations, simulating oxidative stress. Thus, turnover by TRase is unlikely to support GRx2 activity in situ . Supported by NIH R01 AG 024413 & P01 AG 15885, and VA Merit Review (JJM).