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.
Tsakiris
Stylianos
S
Department of Experimental Physiology, Medical School, University of Athens, Greece. stsakir@cc.u-oa.gr
Schulpis
Kleopatra H
KH
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