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 K-m 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 pi-Is, but there are important differences at higher pH values (above neutrality). These properties are compared with these of the ase systems previously reported in these cells.