Catalyzes the reversible reductive amination of pyruvate to L-alanine. Required for proficient utilization of D- or L-alanine as a nitrogen source. May be required for the adaptation from aerobic growth to anaerobic dormancy. It could be involved in the maintenance of the NAD pool during the shift to an anaerobic dormant state in which oxygen as a terminal electron acceptor becomes limiting. H2O + L-alanine + NAD(+) = H(+) + NADH + NH4(+) + pyruvate Optimum pH is between 10 and 11 for the oxidative deamination and between 7 and 7.5 for the reductive amination. Amino-acid degradation; L-alanine degradation via dehydrogenase pathway; NH(3) and pyruvate from L-alanine: step 1/1. Homohexamer. Trimer of dimers. Induced by both D- and L-alanine under aerobic and anaerobic growth conditions, in exponential and stationary phase. In the absence of inducer, high basal levels of activity are observed in cells growing exponentially under anaerobic conditions (at protein level) (PubMed:12193615). Strongly induced immediately after deflection from aerobic growth. Non-essential, it can be deleted. Disruption suppresses alanine dehydrogenase activity, impairs the utilization of alanine as a sole nitrogen source while cells grows to a 10-fold decreased saturation density under anaerobic conditions. Belongs to the AlaDH/PNT family.