NDUFB9 also known as LYRM3, B22 is a subunit of the mitochondrial oxidative phosphorylation complex I (nicotinamide adenine dinucleotide: ubiquinone oxidoreductase). NDUFB9 plays a crucial role as an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase complex I. This complex is essential for cellular respiration, facilitating the transfer of electrons from NADH to the respiratory chain, a process vital for ATP production and overall cellular energy metabolism. NDUFB9 is localized to the inner mitochondrial membrane and the matrix side of the peripheral membrane, which is significant because proper positioning is critical for the efficient functioning of the respiratory chain. The gene encoding NDUFB9 is located on human chromosome 8, a region associated with various diseases, including schizophrenia, bipolar disorder, and certain leukemias, highlighting NDUFB9′s importance in both normal cellular function and disease pathology.