L-Leucine Transport in Isolated Protoplasts ofVincaSuspension Culture: Characterization of Uptake

摘要

The uptake ofL-leucine intoVincaprotoplasts was studied under various conditions. The uptake was highly pH-dependent, with the optimal pH between 3.0 and 4.0. The uptake was also energy dependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited the uptake. Oligomycin,N,N′-dicycIohexyI carbodiimide (DCCD) and vanadate, but not ouabain, inhibited the uptake, suggesting that ATPase for H+electrogenic extrusion was necessary to the uptake ofL-leucine. The uptake showed stereospecificity, but was partially inhibited by otherL-amino acids. A kinetic study of the uptake showed that the uptake was multiphasic with three saturable phases and one unsaturable phase which occurred at concentrations ofL-leucine over 1 mM. TheKmvalues of the three affinity sites were 1.4×10−3M, 1.3×10−4M, 4.3×10−5M; the maximum velocity values were 3.3×10−8, 4.5×10−9, 1.8×10−9mo