Active transport of amino acids by gamma-glutamyl transpeptidase through Caco-2 cell monolayers.
The possible role of the gamma-glutamyl cycle in the transport of amino acids, using the Caco-2 cell monolayer as an in vitro model of the small intestine, has been investigated. The transport of [2-3H]glycine and [2-3H]glycylglycine through the Caco-2 monolayer has been shown to occur by two modes of action. Active transport is unidirectional from apical to basolateral region and is a carrier mediated system. The enzyme gamma-glutamyl transpeptidase seems to be involved in this process, since when the enzyme is inhibited, the active transport is also inhibited. However transport still takes place, and this occurs by a slower non-active process, which is bidirectional and is mediated by passive diffusion. The rate of transport of [2-3H]glycylglycine and [2-3H]glycine were 585 (+/- 24) and 287 (+/- 16) pmolcm-2min-1 respectively, while the non-active transport takes place at 87 (+/- 6) pmolcm-2min-1. Thus, amino acid translocation in Caco-2 cells is shown to occur by two methods, one of which involves the gamma-glutamyl cycle.
Smith
T K
TK
Department of Chemistry, University of Surrey, Guildford, UK.
Gibson
C L
CL
Howlin
B J
BJ
Pratt
J M
JM
D000596:Amino Acids / Q000378:metabolism*; D001692:Biological Transport; D001693:Biological Transport, Active; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003110:Colonic Neoplasms; D005998:Glycine / Q000378:metabolism*; D006033:Glycylglycine / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D000596:Amino Acids; D006033:Glycylglycine; D005723:gamma-Glutamyltransferase; D005998:Glycine