The N-terminal sequence directs import of mitochondrial alanine aminotransferase into mitochondria

Herein, we report cloning and subcellular localization of two alanine aminotransferase (ALT) isozymes, cALT and mALT, from liver of gilthead sea bream (Sparus aurata). CHO cells transfected with constructs expressing cALT or mALT as C- or N-terminal fusion with the enhanced green fluorescent protein (EGFP) showed that cALT is cytosolic, whereas mALT localized to mitochondria. Fusion of EGFP to mALT N-terminus or removal of amino acids 1-83 of mALT avoided import into mitochondria, supporting evidence that the mALT N-terminus contains a mitochondrial targeting signal. The amino acid sequence of mALT is the first reported for a mitochondrial ALT in animals.