Neutral amino acid transporter Ais aproteinthat in humans is encoded by theSLC1A4gene. In melanocytic cells SLC1A4 gene expression may be regulated byMITF. ASCT1 does not transport glutamate or aspartate but alanine, serine, cysteine, and threonine instead. ASCT1 transporter functions primarily as an amino acid exchanger. Transport is associated with a chloride channel activity that is thermodynamically uncoupled from amino acid transport.