. 2018 Mar 7;10(3):322. doi: 10.3390/nu10030322

Table 1.

Characteristics of diverse di- and tripeptide and amino acid transporters expressed in human intestine.

	Encoding Gene	Transporter Protein	Transporter System	Mechanism	Ion Dependency	Dimer Formation	Substrate
Di- and tripeptide transporters
Apical membrane	SLC15A1	PEPT1		S	H⁺		Di- and tripeptide
	SLC15A3	PHT2		S	H⁺		Histidine, di- and tripeptide
	SLC15A4	PHT1		S	H⁺		Histidine, di- and tripeptide
	CDH17	HPT-1		S	H⁺		Di- and tripeptide
Basolateral membrane		Basolateral peptide transporter		U			Di- and tripeptide
Amino acid transporters
Apical membrane	SLC1A1	EAAT3/EAAC1	X⁻_AG	A	AA + 3Na⁺ + H⁺ ↔ K⁺		Aspartic acid and glutamic acid
	SLC1A5	ASCT2/AAAT	ASC	A	Na⁺ + AA ↔ Na⁺ + AA		Neutral amino acids primary substrates: alanine, asparagine, cysteine, glutamine, serine and threonine
	SLC7A9	b^0,+AT	b^0,+	A	CAA/cystine ↔ NAA	rBAT	Cationic amino acids and cystine
	SLC6A6	TauT	β	S	Cl⁻ and 2 Na⁺		β-alanine and taurine
	SLC6A14	ATB^0,+	B^0,+	S	2 Cl⁻ and Na⁺		Cationic and neutral amino acids
	SLC6A19	B⁰AT1/HND	B⁰	S	Na⁺		Neutral amino acids
	SLC6A20	SIT1	IMINO	S	Cl⁻ and 2Na⁺		Proline
	SLC36A1	PAT1/LYAAT1	PAT	S	H⁺		β-alanine, glycine and proline
	SLC38A3	SN1/SNAT3	N	A	AA + Na⁺ ↔ H⁺		Alanine, asparagine, glutamine and histidine
	SLC38A5	SN2/SNAT5	N	A	AA + Na⁺ ↔ H⁺		Asparagine, glutamine, histidine and serine
Basolateral membrane	SLC6A9	GlyT1	Gly⁺	S	Cl⁻ and 2Na⁺		Glycine
	SLC7A1	CAT1	y⁺	U			Arginine, histidine and lysine
	SLC7A6	y⁺LAT2	y⁺L	A	CAA ↔ NAA + Na⁺	4F2hc	Cationic amino acids
	SLC7A7	y⁺LAT1	y⁺L	A	CAA ↔ NAA + Na⁺	4F2hc	Cationic amino acids
	SLC7A8	LAT2	L	A	NAA ↔ NAA	4F2hc	Neutral amino acids
	SLC7A10	asc-1	Asc	A	NAA ↔ NAA	4F2hc	Small neutral amino acids
	SLC7A11	xCT	X_c	A	Cystine ↔ Glutamic acid	4F2hc	Cystine
	SLC38A2	SNAT2	A	S	Na⁺		Neutral amino acids and imino

At the apical membrane there are four peptide transporters expressed by SLC15A1, SLC15A3, SLC15A4 and CDH17 and one on the basolateral membrane with an unknown identity. There are nine apical amino acid transporter systems; SLC1A1 (system X⁻_AG), SLC1A5 (system ASC), SLC3A1 and SLC7A9 (system b^0,+), SLC6A6 (system β), SLC6A14 (system B^0,+), SLC6A19 (system B⁰), SLC6A20 (system IMINO), SLC36A1 (system PAT), SLC38A3 and SLC38A5 (system N). At the basolateral membrane, seven amino acid transporter systems can be distinguished; SLC6A9 (system Gly), SLC7A1 (system y⁺), SLC7A6 and SLC7A7 (system y⁺L), SLC7A8 (system L), SLC7A10 (system Asc), SLC7A11 (system X_C) and SLC38A2 (system A). Amino acid transporters are often referred to by their transporter system in the literature. Mechanisms are depicted by S = symporter, U = uniporter and A = antiporter, as most of them have ion dependency of the required ions [27,30,37,38,39,40,41,42].