(2S)-hydroxybutanoate + NAD(+) = 2-oxobutanoate + NADH + H(+)
(2s)-hydroxybutanoate + nad(+) = 2-oxobutanoate + nadh + h(+)
(2S)-hydroxybutanoate + NAD(+) = 2-oxobutanoate + NADH + H(+)
(2s)-hydroxybutanoate + nad(+) = 2-oxobutanoate + nadh + h(+)