Influx of Glycylsarcosine and l-Lysyl-l-Lysine into Hamster Jejunum in Vitro

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Abstract
The dipeptides glycylsarcosine and L-lysyl-L-lysine may share a single mediated transport mechanism into hamster jejunum, or one of these peptides may be taken up in part by a mediated mechanism unavailable to the other. The investigation, using rings of everted jejunum in vitro, was carried out at pH 5 in order to reduce brush border and/or intramedium hydrolysis of lysyl-lysine. The kinetics of uptake of each peptide was studied over a wide range of concentrations. Estimates of the simple diffusion component in uptake of each peptide were made by the method of self-inhibition of transport as previously described. After correction for simple diffusion, uptake of each peptide conformed to Michaelis-Menten kinetics. Each peptide was capable, at infinitely high concentration, of complete inhibition of mediated uptake of the other. The inhibitory effect was competitive. Glycylsarcosine and lysyl-lysine appear to be taken up by a common mediated mechanism (or possibly mechanisms), neither peptide being taken up by a mediated mechanism unavailable to the other. L-lysyl-L-lysine and glycylsarcosine are taken up by a common mediated mechanism. The neutral dipeptide glycylsarcosine, the acidic dipeptide glutamyl-glutamic acid and the basic dipeptide lysyl-lysine all share a common mediated mechanism for uptake. Peptide uptake may differ from amino acid uptake in that it is indifferent to the net charge on the amino acid side chain(s).