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1Author    Stylianos TsakirisRequires cookie*
 Title    Effects of L-Phenylalanine on Acetylcholinesterase, (Na+,K+)-ATPase and Mg2+-ATPase Activities in Adult Rat Whole Brain and Frontal Cortex  
 Abstract    The effect of different L-phenylalanine (Phe) concentrations (0.12-12.1 m M) on acetylcho­ linesterase (AChE), (Na+,K+)-ATPase and Mg2+-ATPase activities was investigated in ho-mogenates of adult rat whole brain and frontal cortex at 37 °C. AChE, (Na+,K+)-ATPase and Mg2+-ATPase activities were determined after preincubation with Phe. AChE activity in both tissues showed a decrease up to 18% (p<0.01) with Phe. Whole brain Na+,K+-ATPase was stimulated by 30-35% (p<0.01) with high Phe concentrations, while frontal cortex Na+,K+-ATPase was stimulated by 50-55% (pcO.OOl). Mg2+-ATPase activity was increased only in frontal cortex with high Phe concentrations. It is suggested that: a) The inhibitory effect of Phe on brain AChE is not influenced by developmental factors, while the stimulation of Phe on brain Na+,K+-ATPase is indeed affected; b) The stimulatory effect of Phe on rat whole brain Na+,K+-ATPase is decreased with age; c) Na+,K+-ATPase is selectively more stimulated by high Phe concentrations in frontal cortex than in whole brain homogenate; d) High (toxic) Phe concentrations can affect Mg2+-ATPase activity in frontal cortex, but not in whole brain, thus modulating the amount of intracellular Mg2+. 
  Reference    Z. Naturforsch. 56c, 132—137 (2001); received September 4/October 4 2000 
  Published    2001 
  Keywords    Acetylcholinesterase, (Na+, K+)-, Mg2 +-ATPase, L-Phenylalanine 
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 TEI-XML for    default:Reihe_C/56/ZNC-2001-56c-0132.pdf 
 Identifier    ZNC-2001-56c-0132 
 Volume    56 
2Author    Stylianos Tsakiris3, Panagiota Kouniniotou-Krontiri3, KleopatraH. Schulpisb, JohnC. Stavridis3Requires cookie*
 Title    L-Phenylalanine Effect on Rat Brain Acetylcholinesterase and Na+,K+-ATPase  
 Abstract    The effect of different L-phenylalanine (Phe) concentrations (0 .1 -1 2 .1 m M) , on acetylcho­ linesterase (A C h E) and N a+,K +-ATPase activities of brain homogenate and pure enzymes, was investigated at 37 °C. A C h E and Na+,K +-ATPase activities were determined according to Ellman G. -6 1 3) respectively, after preincubation with Phe. A C h E activity in brain homogenate or in pure eel E.electricus enzyme showed a decrease, which reached up to 18% with concentrations of 0 .9 -1 2 .1 m M . Brain homogenate N a+,K +-A TPase activity showed an increase 1 6 -6 5 % with 0 .2 4 -0 .9 mM of Phe, while an activity increase of 6 0 -6 5 % appeared with 0 .9 -1 2 .1 mM of Phe. Pure en­ zyme activity (from porcine cerebral cortex) was not affected by high Phe concentrations, while it was increased by low concentrations. The above results suggest: a) A direct effect of Phe on A C h E , b) A direct effect of low Phe concentrations and an indirect effect of high ones on Na+,K +-ATPase. 
  Reference    Z. Naturforsch. 53c, 163 (1998); received September 22/D ecem ber 15 1997 
  Published    1998 
  Keywords    L-Phenylalanine, R at Brain, Acetylcholinesterase, N a+, K +-ATPase, Mg2+-ATPase 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0163.pdf 
 Identifier    ZNC-1998-53c-0163 
 Volume    53 
3Author    Stylianos Tsakiris3, Panagoula Angelogianni3, KleopatraH. Schulpisb, Panagiotis Behrakis3Requires cookie*
 Title    Protective Effect of L-Cysteine and Glutathione on Rat Brain Na+,K+-ATPase Inhibition Induced by Free Radicals  
 Abstract    The aim of this study was to investigate whether the preincubation of brain homogenates with L-phenylalanine (Phe), L-cysteine (Cys) or reduced glutathione (G SH) could reverse the free radical effects on N a+,K+-ATPase activity. Two well established systems were used for the production of free radicals: 1) F e S 0 4 (84 ^i m) plus ascorbic acid (400 |o.m) and 2) F e S 0 4, ascorbic acid and H20 2 (1 mM) for 10 min at 37 °C in hom ogenates o f adult rat whole brain. Changes in brain N a+,K+-ATPase activity and total antioxidant status (TAS) were studied in the presence of each system separately, with or without Phe, Cys or GSH. TAS value reflects the amount of free radicals and the capacity of the antioxidant enzymes to limit the free radicals in the homogenate. N a+,K+-ATPase was inhibited by 35 -5 0 % and TAS value was decreased by 5 0 -6 0 % by both systems of free radical production. The enzy­ matic inhibition was completely reversed and TAS value increased by 150-180% when brain homogenates were preincubated with 0.83 mM Cys or GSH. However, this N a+,K+-ATPase inhibition was not affected by 1.80 m M Phe, which produced a 4 5 -5 0 % increase in TAS value. It is suggested that the antioxidant action of Cys and GSH may be due to the binding of free radicals to sulfhydryl groups of the m olecule, so that free radicals cannot induce N a+,K+-ATPase inhibition. Moreover, Cys and GSH could regulate towards normal values the neural excitability and metabolic energy production, which may be disturbed by free radical action on N a+,K+-ATPase. 
  Reference    Z. Naturforsch. 55c, 271—2 (2000); received October 8/Decem ber 21 1999 
  Published    2000 
  Keywords    L-Cysteine, Reduced Glutathione, L-Phenylalanine, Free Radicals, N a+, K+-ATPase 
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 TEI-XML for    default:Reihe_C/55/ZNC-2000-55c-0271.pdf 
 Identifier    ZNC-2000-55c-0271 
 Volume    55