Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) that is believed to belong to the minimal assembly required for 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 (By similarity). a ubiquinone + 5 H(+)(in) + NADH = a ubiquinol + 4 H(+)(out) + NAD(+) Complex I is composed of at least 49 different subunits. Exons a and b (AtMg00285) and c, d and e (AtMg01320) are cis-spliced, while a trans-splicing reaction is required to link exons b and c. A stretch of 270 kb of the mitochondrial genome is duplicated within the centromere of chromosome 2 resulting in the duplication of the gene. The expression of this duplicated gene (At2g07733 and At2g07689) is not demonstrated. It is also probably not RNA edited and therefore differs in all the positions known to be edited.