(R)-2-hydroxyglutarate + A => 2-oxoglutarate + AH2
(r)-2-hydroxyglutarate + a => 2-oxoglutarate + ah2
(R)-2-hydroxyglutarate + A => 2-oxoglutarate + AH2
(r)-2-hydroxyglutarate + a => 2-oxoglutarate + ah2