Evidence that cycloleucine affects the high-affinity systems of amino acid uptake in cultured human fibroblasts.
The influence of cycloleucine on kinetic parameters of uptake of L-alanine, L-proline and L-leucine into cultured human fibroblasts was examined under initial-rate conditions with substrate concentrations of 0.05-10 mM and 5 mM-cycloleucine. Kinetic data obtained by computer analysis showed that, in the absence of cycloleucine, cell uptake was heterogeneous for each amino acid. L-Alanine and L-leucine entered by two transport systems with different affinities; L-proline was taken up by one saturable transport system plus a diffusion-like process. This heterogeneity disappeared in the presence of cycloleucine, since the high-affinity systems were no longer detectable. The remaining process had the same kinetic constants as the low-affinity system for alanine and leucine and a KD similar to the diffusion constant for proline. The influence of cycloleucine on the amino acid uptake was not specific either to the amino acid concerned or to a particular transport system, since the three neutral amino acid-transport systems, A, ASC and L, were involved in these experiments. This influence was shown to be unaffected by the absence of Na+ (for leucine uptake). ATP content of the cells was identical in the presence or in the absence of cycloleucine.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism* / Q000494:pharmacology*; D002478:Cells, Cultured; D003515:Cycloleucine / Q000494:pharmacology*; D003864:Depression, Chemical; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D003515:Cycloleucine; D000255:Adenosine Triphosphate; D011392:Proline; D012964:Sodium; D007930:Leucine; D000409:Alanine