Magnesium (Mg2+) is required for the catalytic activity of numerous metalloenzymes within a variety of subcellular organelles. Magnesium transporter MRS2 homolog, mitochondrial (MRS2) mediates the influx of Mg2+ into the mitochondrial matrix (Zsurka et al. 2001). MRS2 is located on the inner mitochondrial membrane and its expression in yeast with a Mrs2-1 knock-out mutant partly restores mitochondrial magnesium concentrations that are otherwise much reduced (Zsurka et al. 2001).