The biomimic reactions of N phosphoryl amino acids are very important in the study of many biochemical processes, it was found that the α-COOH group, and not the γ-COOH, was involved in the ester exchange on phosphorus experimentally. The reactions, had been proposed to be related to intramolecular penta coordinate phosphoric carboxylic mixed anhydiides. N Dimethylphosphoryl glutamic acid (DMP Glu) was selected as model compound to study the reactivity difference between the α-COOH and γ-COOH group. From MNDO calculations, the energy of the penta coordinate phosphoric intermediates contain ing five membered ring from a COOH was 40.8 ld/mol lower than that of the seven membered one from γ-COOH. This resnlt was in agreement with those from HF/6-31G** and B3LYP/6 31G** calculations. Theoretical tln-ee dimensional potential energy snrface of frothing the intermdiates predicted that the transition states 4 and 5 involving α-COOH or γ-COOH gronp had energy baniers of △E=196.1 and 216.9 kJ/mol, respectively. So the α-COOH conld be differentiated from γ-COOH intramolecnlarly in glutantic acid by N phosphorylation.