A novel imino-acid carrier in the enterocyte basolateral membrane.
Basolateral membrane vesicles prepared from rat small intestinal epithelial cells were used to study the sodium-independent transport of L-proline. The uptake of L-proline was unaffected by the presence of sodium and showed saturation kinetics (Kt = 0.5 mM and Vmax = 23.3 pmol/mg protein per s). Competition experiments indicated that other amino acids had an affinity for the carrier system with L-leucine greater than L-alanine greater than sarcosine greater than glycine greater than L-lysine greater than OH-proline greater than taurine greater than beta-alanine greater than D-alanine greater than D-proline greater than L-serine greater than phenylalanine greater than valine greater than D-serine greater than phenylalanine greater than valine greater than D-serine greater than MeAIB greater than methionine greater than threonine. This pathway does not resemble those previously described either in the brush-border membrane of intestinal epithelial cells or the plasma membrane of other cell types. The lack of effect of methionine and threonine indicate that proline is not using the L-type system, while the very low affinity for MeAIB and the Na+ independence suggest that this is a novel system for imino acids. The relatively high capacity of this system and its low Kt, which is almost identical to the proline system in the brush-border membrane, strongly suggest that this is an important pathway in the final step for proline absorption by the small intestine.
D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D007098:Imino Acids / Q000378:metabolism; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D011392:Proline / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D007098:Imino Acids; C041832:proline transport protein; D011392:Proline