heh the letters before the amino acid denote avery interesting chemistry thing that i read a lot about you have to google "chiralty" or "isomers" kinda not the easist thing to grasp , and yeh obv it goes phe->tyr-> then on to l-dopa and the catacholamines(epi norepi dopa) so tyr is futher along in the conversion process but if phe works then cool...gl