(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