(S)-2-hydroxyglutarate + A <=> 2-oxoglutarate + AH2
(s)-2-hydroxyglutarate + a <=> 2-oxoglutarate + ah2
(S)-2-hydroxyglutarate + A <=> 2-oxoglutarate + AH2
(s)-2-hydroxyglutarate + a <=> 2-oxoglutarate + ah2