Amino Acid Transport in Plants and Transport of Neurotransmitters in Animals: a CommonMechanism? - Communication in Plants: Neuronal Aspects of Plant Life - page 158

The first one (SLC36A1, LYAAT1, PAT1) was identified as a lysosomal AA
transporter, which mediates proton-coupled export of AA from lysosomes
(Sagne et al. 2001). LYAAT1 was also localized to the apical membrane in
intestine cells, where it mediates proton-driven uptake of small neutral AA
(Thwaites et al. 1995). Like PAT1, SLC36A2 (PAT2) mediates proton symport
uptake of small neutral AA. In addition, the SLC36 family comprises two
orphans, SLC36A3 and SLC36A4.
11.2.7
The Sodium-Coupled Neutral Amino Acid
Transporter Family (SNAT, SLC38)
In mammals transporters from the SLC38 family play various roles. For ex-
ample, a role for SNAT2 in the provision of AA entering the gluconeogenic
pathway could be suggested. SNAT3 may play a role in the response to aci-
dosis in rats (Karinch et al. 2002) or could be involved in the detoxification
of ammonia from the portal blood in the liver (Mackenzie and Erickson
2004). Recently Mackenzie and Erickson (2004) renamed the SLC38 mem-
bers SNAT1-6. SNAT stands for sodium-coupled neutral AA transporter
and also recalls the classic transport activities, i.e., system N/A trans-
porter. SNAT1 (former ATA1, GlnT, NAT2, SA2, SAT1), SNAT2 (former
ATA2, KIAA1382, SA1, SAT2) and SNAT4 (former ATA3, FLJ10191, NAT3,
PA AT, S AT 3 ) b e l on g t o t h e s y s t e m A s u b f a m i l y t r a n s p o r t i n g a l i p h at i c A A
in correlation with an uptake of Na + (Mackenzie and Erickson 2004).
System A members are pH-sensitive and underlie a sophisticated hor-
monal and adaptive regulation (Häussinger and Kilberg 1992; McGivan
and Pastor Anglada 1994; Shotwell et al. 1981). SNAT3 [former g17, NAT
(mouse), SN1; Fig. 11.1 and SNAT5 (former JM24, SN2) correspond to
a second kind of system, namely, system N. SNAT3 and SNAT5 are like sys-
tem A Na + -dependent. Glutamine, histidine and asparagine belong to the
substrates transported by system N, whereas system A is not that limited,
transporting alanine, asparagine, cysteine, glutamine, glycine, methionine
and serin (Mackenzie et al. 2004). Transport is also coupled with a H +
countertransport which produces a low extracellular pH that inhibits the
system (Albers et al. 2001; Broer et al. 2002; Chaudhry et al. 1999, 2001, 2002;
Nakanishi et al. 2001). As in system A, the regulation of system N is adaptive
(Jacob et al. 1986; Kilberg et al. 1980). SNAT6 [former NAT-1 (human)], the
orphan member of the SLC38 family has been isolated from a human brain
complementary DNA (cDNA) library (Mackenzie and Erickson 2004).
Note that SLC32, SLC36 and SLC38 members can be grouped in an
eukaryotic specific superfamily, namely the ATF1 superfamily (Sect. 11.3.2)
(Wipf et al. 2002; Fig. 11.3).