Characteristics of D-leucine uptake by mouse Ehrlich ascites tumor cells.
In a previous paper, we reported that various D-amino acids were taken up several times more effectively than the corresponding L-isomers into several tumors tested in vivo. In order to investigate this further, the in vitro uptake of D-[14C]leucine by Ehrlich ascites tumor cells was investigated in comparison with that of L-[14C]leucine. The distribution ratio, the effects of amino acids and pH, and an approximately linear Lineweaver-Burk plot indicated that D-leucine was transported by an active transport system for L-leucine. Vmax and ku, the first-order rate constant for the unsaturable component, for the uptake of D- and L-leucines decreased with a fall in temperature. The activation energies for Vmax and ku were in the range of 5-10 and 18-21 kcal/mol, respectively. The values for L-leucine were greater than those for D-leucine. Km for D-leucine transport increased with decreasing temperature, whereas Km for L-leucine decreased. This difference suggests that the large alkyl chains of D- and L-leucines bind to different portions of a carrier protein.
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D004140:Dinitrophenols / Q000494:pharmacology; D007536:Isomerism; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008297:Male; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013696:Temperature
D000596:Amino Acids; D004140:Dinitrophenols; D010042:Ouabain; D007930:Leucine