Complex I is the largest protein complex of the oxidative phosphorylation system in mitochondrial and it catalyzes NADH-quinone oxidoreduction. Complex I represents the main entrance site for electrons into the respiratory electron transfer chain. In Arabidopsis, Complex I have at least 49 subunits and CAL1 (AT5G63510) is one of the subunit. CAL2 (At3g48680) is also a subunit of Complex I.
