| Amino acids are essential components in cellular metabolism. Even through these amino acids are divided into the essential amino acids and the nonessential amino acids, most of the amino acids have to be supplied to the cell via multiple membrane transport systems in the forms of free amino acids or peptides. On the molecular level, the cDNA homologues of rATB0 (from human Caco-2 cell line), rASCT1, rATB0 (from rat liver cells), mPHT1 (from mouse brain), mPEPT1, mPEPT2 (from mouse kidney tissue) have been cloned, sequenced, and functionally expressed in the Hela cells and X. laevis oocytes. The following important conclusions have been well established. (1) The human intestinal cell line Caco-2 and the human placental choriocarcinoma cell line JAR express an identical neutral amino acid transport system ATB0. (2) The liver cells not only express the neutral amino acid transport system ASM but also express a different neutral amino acid system ATB0. (3) The mouse kidney expresses both peptide transport systems (PEPT1 and PEPT2). We have also cloned and characterized the mouse gene for PEPT1, the structure features of PEPT1 gene have been completely described. |
