Reductase component of a two-component system involved in the degradation of tertiary alcohols such as tert-butyl alcohol (TBA) and tert-amyl alcohol (TAA) (PubMed:22194447). MdpK probably provides electrons via its [2Fe-2S] iron-sulfur cluster to the MdpJ oxygenase subunit (Probable). Binds 1 2Fe-2S cluster. This two-component enzyme is composed of an oxygenase (MdpJ) and a reductase (MdpK). Induced in the presence of tert-butyl alcohol (TBA). Belongs to the PDR/VanB family.