NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 9 is a protein in humans that is encoded by NDUFB9 gene. Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed to be not 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.