Alanine reverses the inhibitory effect of phenylalanine on acetylcholinesterase activity.
The aim of this work was to evaluate, in vitro, the effect of L-alanine (Ala) on suckling rat brain acetylcholinesterase (AChE) and on eel Electrophorus electricus pure AChE inhibited by L-phenylalanine (Phe) as well as to investigate whether Phe or Ala is a competitive inhibitor or an effector of the enzyme. AChE activity was determined in brain homogenates and in the pure enzyme after 1 h preincubation with 1.2 mM of Phe or Ala as well as with Phe plus Ala. The activity of the pure AChE was also determined using as a substrate different amounts of acetylthiocholine. Ala reversed completely the inhibited AChE by Phe (18-20% in 500-600 microM substrate, p<0.01). Lineweaver-Burk plots showed that Vmax remained unchanged. However, Km was found increased with Phe (150%, p<0.001), decreased with Ala alone (50%, p<0.001) and unaltered with Phe plus Ala. It is suggested that: a) Phe presents a competitive inhibitory action with the substrate whereas Ala a competitive activation; b) Ala competition with Phe might unbind the latter from AChE molecule inducing the enzyme stimulation; c) Ala might reverse the inhibitory effect of Phe on brain AChE in phenylketonuric patients, if these results are extended into the in vivo reality.
Department of Experimental Physiology, Medical School, University of Athens, Greece. stsakir@cc.u-oa.gr
Stylianos
S
Tsakiris
Kleopatra H
KH
Schulpis
D000110:Acetylcholinesterase / Q000378:metabolism*; D000409:Alanine / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D007700:Kinetics; D008297:Male; D010649:Phenylalanine / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity
D004791:Enzyme Inhibitors; D010649:Phenylalanine; D000110:Acetylcholinesterase; D000409:Alanine