CAT1, CAT2, CAT2a and CAT3). Of these,
CAT1, CAT2 and CAT3 cDNAs encode high-
affinity cationic amino acid transport
(micromolar Kmvalues). Based on hydro-
phobicity profiles, all three transporters are
predicted to possess 12–14 membrane-
spanning domains. CAT1 mRNA is
ubiquitously expressed, being present in all
tissues tested except for the liver (Deves
and Boyd, 1998). In mice, CAT1 protein is
the recognition receptor for infection by the
murine ecotropic leukaemia virus (MacLeod
et al., 1994). That mice have not evolved to
eliminate this source of viral recognition
suggests that CAT1 is indispensable in its
role of supplying cells with the essential
amino acids arginine, lysine and histidine.
In humans, CAT2 mRNA is expressed less
widely than CAT1, with the highest levels
of mRNA expressed in skeletal muscle,
placenta and ovaries, followed by lower
expression in liver, pancreas, heart and
kidney. CAT3, however, is only expressed
in significant amounts in the brain.10 J.C. Matthews
Table 1.3.Free and peptide-bound -amino acid transport proteins for which there are cDNA clonesa.
Alternate Deduced Transport Substrate Substrate Ions
Clone names lengthb system specificity affinity coupled
CAT1 — 622–629 y+c Cationic μM —
CAT2 CAT2a 657–658 y+ Cationic μM —
CAT2a CAT2b 657–659 y+ Cationic mM —
CAT3 — 619 y+ Cationic μM —
EAAT1 GluT, GLAST 543 XAG D,L-aspartate μM Na+in, K+out,
L-glutamate OH/HCO 3 out
EAAT2 GLT, GLAST2, 573 XAG D,L-aspartate μM Na+in, K+out,
GLTR L-glutamate OH/HCO 3 out
EAAT3 EAAC1 523–525 XAG D,L-aspartate μM Na+in, K+out,
L-glutamate OH/HCO 3 out
EAAT4 — 564 XAG D,L-aspartate μM Na+in, K+out,
L-glutamate OH/HCO 3 out
EAAT5 — 561 XAG D,L-aspartate μM Na+in, K+out,
L-glutamate OH/HCO 3 out
ASCT1 SATT 532 ASC Neutral (pH 7.5) μM Na+in
Anionic (pH 5.5)
ASCT2 ATBo 553 ASC Neutral μM Na+in
NBAT Naa-Tr, 683 bo,+ Neutral μM —
D2 cationic
and cystine
4F2hc — 529 y+L Neutral and μM Na+in(for neutral)
cationic
PepT1 — 707–708 H+/peptide Di-, tri-, tetra- mM H+in
peptides and Abd
PepT2 — 729 H+/peptide Di-, tri-, tetra- μM H+in
peptides and Abd
aDoes not include members of the family of brain-specific neurotransmitter transporters (PROT, GLYT1a,
GLYT1b, GLYT1c, GLYT2; Malandro and Kilberg, 1996).
bPredicted number of amino acids.
cIn mice, also acts as the recognition site for murine ecotropic leukaemia virus.
d-Lactam and cephalosporin antibiotics.