Uptake of L-leucine by trout red blood cells and peripheral lymphocytes

The uptake of l-leucine by trout red blood cells and peripheral lymphocytes has been analyzed. The present study shows two functionally different Na+-independent systems for apolar branched-chain amino acids. They are designated as L systems because they share some properties with the mammalian L system. The carrier present in red blood cells has low Km values, is trans-stimulable and not stereospecific for leucine uptake; on the other hand, the system present in lymphocytes is stereospecific for leucine uptake and trans-inhibitable. Both carriers are pH sensitive in a similar fashion at low pHs, but there are important differences at higher pH values (above neutrality). These properties are compared with these of the asc systems previously reported in these cells.