Table 1.

Properties of representative PepT1 substrates in wild-type (WO) and knockout (KO) mice

Substrate	Classification	MW	pKa (Values)a	WT Peff (x 10−4 cm/s)b	KO Peff (x 10−4 cm/s)e
5-Amino- levulinic acid	Non-Peptide Mimetic	131		2.00	0.20
Glycyl- sarcosine	Synthetic Dipeptide	146		1.70	0.15
Val- acyclovir	Peptide-Like Prodrug	324		1.68 (1.66)c	0.05
Cef- adroxil	Peptide-Like Drug	363		0.81 (1.56)d	0.09

^apKa values were reported for 4-aminolevulinic acid (Product Information, Sigma-Aldrich, St. Louis, MO), glycylsarcosine (Irie et al., 2005), valacyclovir (Balimane and Sinko, 2000) and cefadroxil (Tsuji et al., 1981).

^bPeff is the jejunal permeability of 4-aminolevulinic acid (Xie et al., 2012), glycylsarcosine (Wu et al., 2009), valacyclovir (Yang et al., 2010) and cefadroxil (Posada and Smith, 2011b) in wild-type mice as determined by in situ single-pass perfusions.

^cPeff is the jejunal permeability of valacyclovir in humans as determined by in vivo single-pass perfusions (Lennernäs, 2007).

^dPeff is the jejunal permeability of a similar aminocephalosporin, cephalexin, in humans as determined by in vivo single-pass perfusions (Lennernäs, 2007).

^ePeff is the jejunal permeability of 4-aminolevulinic acid (Xie et al., 2012), glycylsarcosine (Wu et al., 2009), valacyclovir (Yang et al., 2010) and cefadroxil (Posada and Smith, 2011b) in Slc15a1 knockout mice as determined by in situ single-pass perfusions.