... Chal-font, UK). Dexamethasone, apotransferrin, Gly-Gln, Ala-Ala, Ala-Ala-Ala, Lys-Lys, d-aminolevulinic acid, cefadroxil,Gly, Pro-Ala, 8-aminooctanoic acid and Gly-Sar were fromSigma-Aldrich ... 105 ± 3Lys-Lys 46 ± 2Ala-Asp 19 ± 1D-Phe-Ala 65 ± 2Ala-Ala-Ala 21 ± 1d-Aminolevulinic acid 78 ± 3Cefadroxil 15 ± 1Lys[Z(NO2)]-Val 10 ± 18-Aminooctanoic acid 111 ± 3Ala-4-nitroanilide ... Gly-Sar,Ala-Ala, Lys-Lys, Ala-Asp, d-Phe-Ala, Ala-Ala-Ala,d-aminolevulinic acid, cefadroxil and Ala-4-nitroanilide(all 100 lm, Table 1). Glycine, which is not a substrateof peptide transporters,...