_L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture : Characterization of Uptake

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The uptake of L-leucine into Vinca protoplasts 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 cyanide m-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited the uptake. Oligomycin, N,N'-dicyclohexyl carbodiimide (DCCD) and vanadate, but not ouabain, inhibited the uptake, suggesting that ATPase for H^+ electrogenic extrusion was necessary to the uptake of L-leucine. The uptake showed stercospecificity, but was partially inhibited by other L-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 of L-leucine over 1 mM. The K_m values of the three affinity sites were 1.4 × 10^<-3> M, 1.3 × 10^<-4> M, 4.3 × 10^<-5> M; the maximum velocity values were 3.3 × 10^<-8>, 4.5 × 10^<-9>, 1.8 × 10^<-9> mol/10 min/4 × 10^6 cells.
日本植物生理学会の論文