Human Small Peptide Transporter

Walker, D., et al. Substrate upregula-tion of the human small intestinal peptide transporter, hPepTl. J. Physiol. 1998, 507, 697-706. 

There does not appear to be any significant proteolytic degradation by enzymes in the extracellular fluid in normal human airways and alveoli. However, the presence of peptidases makes absorption of small peptides variable and difficult to predict. Peptidase-resistant peptides generally show better bioavailabilities than other peptides with comparable molecular weights. ° Difference in metabolism and absorption of d and L forms of peptides glycyl-D-phenylalanine and glycyl-L-phenylalanine was demonstrated by Morimoto et al.f The l peptide was subject to metabolism, and it had significant paracellular transport with a smaller transcellular component. In contrast, the... 

The PEPTs are hydrogen ion-dependent transporters that transport small peptides and proteinlike compounds such as cephalosporins, penicillin, enalapril, and cap-topril. Humans express two distinct PEPTs designated PEPT1 and PEPT2. PEPT1... 

Only one publication has presented data to support the idea that higher frequency (1 MHz) US can be used to increase peptide delivery across the skin. ° The enhanced transport of poly-L-lysine (MW = 4-kDa) across human epidermis has been reported, a finding completely at odds with the relatively modest action of US at this frequency on the percutaneous penetration of several small molecular weight substances. ... 

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