Modulation of glutamine uptake and phosphate-activated glutaminase activity in rat brain mitochondria by amino acids and their synthetic analogues

Uptake of L-[C-14] Gin and phosphate-activated glutaminase (PAG) activity w ere measured in nonsynaptic mitochondria isolated from rat cerebral hemisph eres, in the presence of protein and nonprotein amino acids and their synth etic structural analogues and derivatives. The uptake was inhibited by > 50 % in the presence of a 10-fold excess of His, homocysteine (Hcy), Trp, Leu, Tyr, lie, Thr, Ala, Phe, Met, Ser, by > 20% in the presence of a 10-fold e xcess of Val, Arg, Glu, and was not affected by a 10-fold excess of Orn, al pha-ketoglutarate, Tau and Pro. Uptake of L-[C-14] Leu differed from Gin up take by its resistance to Arg, Glu, and a relatively high sensitivity to th e reference inhibitor of the plasma membrane transport of large neutral ami no acids (L-system) - BCH (2-aminobicyclo[2.2.1]heptane-2-carboxylic acid), and a number of natural L-system substrates. A newly synthesized alanine a nalogue, 2'-cyano-(biphenyl) alanine, referred to as MRC01, was the only co mpound tested that inhibited Gin uptake more strongly than Leu uptake. The strongest Gin uptake inhibitors: MRC01, His, Hey and Leu, inhibited PAG act ivity by > 50% when added at the inhibitor/Gln concentration ratio of 1:2. PAG activity was not affected by Tau, Lys or Pro, compounds which did affec t Gin uptake. The results suggest that a number of natural amino acids func tion as common endogenous modulators of cerebral mitochondrial Gin uptake a nd its degradation. MRC01, because of its inhibitory potency towards both m itochondrial Gin uptake and PAG activity, may become a convenient tool in s tudying the role of Gin transport in its mitochondrial metabolism in intact CNS cell and tissues. (C) 2000 Elsevier Science Ltd. All rights reserved.