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

Uptake of L-14C]Gln and phosphate-activated glutaminase (PAG) activity were measured in nonsynaptic mitochondria isolated from rat cerebral hemispheres, in the presence of protein and nonprotein amino acids and their synthetic 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, Ile, Thr, Ala, Phe, Met, Ser, by > 20% in the presence of a 10-fold excess of Val, Arg, Glu, and was not affected by a 10-fold excess of Orn, alpha-ketoglutarate, Tau and Pro. Uptake of L-14C] Leu differed from Gln uptake by its resistance to Arg, Glu, and a relatively high sensitivity to the reference inhibitor of the plasma membrane transport of large neutral amino acids (L-system)--BCH (2-aminobicyclo2.2.1]heptane-2-carboxylic acid), and a number of natural L-system substrates. A newly synthesized alanine analogue, 2'-cyano-(biphenyl) alanine, referred to as MRC01, was the only compound tested that inhibited Gln uptake more strongly than Leu uptake. The strongest Gln uptake inhibitors: MRC01, His, Hcy and Leu, inhibited PAG activity 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 affect Gln uptake. The results suggest that a number of natural amino acids function as common endogenous modulators of cerebral mitochondrial Gln uptake and its degradation. MRC01, because of its inhibitory potency towards both mitochondrial Gln uptake and PAG activity, may become a convenient tool in studying the role of Gln transport in its mitochondrial metabolism in intact CNS cell and tissues.