<p>L-Phenylalanine is produced by reacting cinnamic acid and ammonia yielding substance in the presence of L-phenylalanine ammonia lyase (PAL). Combined use of the ammonium salt of a lower carboxylic acid, ammonium carbonate and ammonium hydroxide as the ammonia yielding substance makes it possible to obtain stable PAL activity even at high ammonia concentrations of 10 mol/ l and over. Moreover, no salting-out of PAL takes place so that the reduction of effective PAL concentration due to salting-out of PAL can be avoided. Efficient production of L-phenylalanine is therefore feasible.</p>
