NADH dehydrogenase (ubiquinone) 1 beta subcomplex subunit 9, also known as NDUFB9, belongs to the complex I LYR family. Localized to the inner mitochondrial membrane, as well as to the matrix side of the peripheral membrane, NDUFB9 functions as an accessory subunit of the multi-subunit mitochondrial membrane respiratory chain NADH dehydrogenase complex I. Complex I plays an important role in the transfer of electrons from NADH to the respiratory chain, a process that is essential for cellular respiration. Recombinant human NDUFB9 protein, fused to His-tag at N-terminus, was expressed in E.coli.