Reductase component of the propane 2-monooxygenase multicomponent enzyme system which is involved in the degradation of propane via the O2-dependent hydroxylation of propane. Reductase catalyzes the transfer of electrons from NADH or NADPH to monooxygenase (Probable). Binds 1 2Fe-2S cluster. The propane 2-monooxygenase multicomponent enzyme system is composed of an electron transfer component and a monooxygenase component interacting with the effector protein PrmD. The electron transfer component is composed of a reductase (PrmB), and the monooxygenase component is formed by a large subunit (PrmA) and a small subunit (PrmC). By propane. Belongs to the TmoA/XamoA family.