Agriculture Reference
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AA (Verrey et al. 2004). Mammalian HATs are composed of a light subunit
(LAT-1, y
+
LAT1, y
+
LAT-2, LAT-2, b
o
,+
AT, Asc-1, xCT and two orphans) and
a heavy subunit (“heavy chain, SLC3”) (Ganapathy et al. 2001, Palacin et
al. 1998). The heavy subunit is required for the generation of active plasma
membrane AA transporters. This subunit is glycosylated, contains only one
putative transmembrane domain and plays a role in trafficking to target
membranes, for example, in polarized epithelial cells (Palacin et al. 1998).
Six of the known light chains associate with 4F2hc, the widespread heavy
subunit, strictly basolateraly localized in epithelia (Verrey et al. 2004).
A second heavy subunit, the brush border localized rBAT, was identified in
mammals. So far, SLC3 homologs have not been found in plants.
11.2.4
The Type I Phosphate Transporter Family (SLC17)
The transport of organic anions is the primary function of the SLC17
family, which contains four type I phosphate transporters (SLC36A1-4),
a lysosomal sialic acid transporter (SIALIN, SLC36A5) and, surprisingly,
three vesicular glutamate transporters [VGLUT1 (or BNP1), VGLUT2-3,
(SLC36A6-8)] occurring in synaptic vesicles (Fig. 11.1) (Reimer and Ed-
wards 2004). All three VGLUT have been shown to have a
K
m
for glu-
tamate around 1 mM (Bai et al. 2001; Bellocchio et al. 2000; Fremeau
et al. 2002). Homologs of SLC17 members have been identified in plant
genomes without being more closely characterized (Reimer and Edwards
2004) (Sect. 11.3.2).
11.2.5
The Vesicular Inhibitory Amino Acid
Transporter Family (VIAAT, SLC32)
This family includes a single member, the vesicular inhibitory AA trans-
porter (VIAAT) or vesicular GABA transporter (VGAT, Fig. 11.1) (Gasnier
2004). VGAT is localized on synaptic vesicles (Fig. 11.1), where it mediates
theuptakeofGABAandglycineintosynapticvesiclesandtheirexocytotic
release (Gasnier 2004; McIntire et al. 1997).
11.2.6
The Proton/Amino Acid Transporter Family (PAT, SLC36)
The SLC36 family comprises four members which encode around 500 AA
proteins and have 11 predicted transmembrane domains (Boll et al. 2004).
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