2.A.18.8.7
Proton-coupled amino acid transporter 1 (Proton/amino acid transporter 1) (hPAT1 or LYAAT-1) (Solute carrier family 36 member 1).  SLC36A1 is expressed at the luminal surface of the small intestine but is also commonly found in lysosomes in many cell types (including neurons), suggesting that it is a multipurpose carrier with distinct roles in different cells including absorption in the small intestine and as an efflux pathway following intralysosomal protein breakdown. SLC36A1 has a relatively low affinity (K_m = 1-10 mM) for its substrates, which include zwitterionic amino and imino acids, heterocyclic amino acids and amino acid-based drugs and derivatives used experimentally and/or clinically to treat epilepsy, schizophrenia, bacterial infections, hyperglycaemia and cancer (Thwaites and Anderson 2011).  hPAT1 transports the pyridine alkaloids, arecaidine, guvacine and isoguvacine, across the apical membrane of enterocytes and might be responsible for the intestinal absorption of these drug candidates (Voigt et al. 2013).