L-phenylalanine effect on rat diaphragm acetylcholinesterase and Na+,K+-ATPase

The effect of different L-phenylalanine (Phe) concentrations (0.24-12.1 mM) , on acetylcholinesterase (AChE) and Na+,K+-ATPase activities of diaphragm homogenates from 21-day old rats and pure enzymes, was investigated at 37 d egrees C. AChE and Na+,K+-ATPase activities were determined after preincuba tion with Phe. AChE activity in diaphragm homogenate or in pure eel E. elec tricus enzyme showed a decrease, which reached a maximum of 18% with Phe co ncentrations of 0.9-12.1 mM. However lower Phe concentrations (0.24 mM) inc reased the enzyme activity (by approximately 22%), only in the diaphragm ho mogenate. Diaphragm-associated Na+,K+-ATPase activity showed a progressive and concentration-dependent decrease, by about 30-35% in the presence of hi gh Phe concentrations. Pure enzyme activity (from porcine cerebral cortex) was not affected by high Phe concentrations (>0.48 mM), while it was increa sed by low concentrations. The above results suggest: a) A direct inactivat ing effect of high Phe concentrations on AChE and an indirect activating ef fect induced by low concentrations. b) A direct activating effect of low Ph e concentrations and an indirect inactivating effect of high ones on Na+,K-ATPase. c) The combination of high Phe concentrations effects on AChE and Na+,K+-ATPase could influence the levels of the diaphragm synaptic ACh.