NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 4 is a protein in humans that is encoded by NDUFB4 gene. Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone.