This study utilizes ab initio calculations to investigate the reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) between amino acids and spillover tritium. The Hartree-Fock approximation and second-order Moller-Plesset perturbation theory in conjunction with 6-31G* and aug-cc-pVDZ basis sets were used to calculate potential energy surfaces for the interactions between CH4, alanine, hydroxyproline, and the H3O+ ion. Ab initio calculations were used to estimate the activation energies and structures of the transition states of these reactions. The hydrogen exchange reaction occurs by a synchronous mechanism, with a transition state that is characterized by pentacoordinated carbon. The proposed one-center mechanism is in good agreement with observed retention of configuration of the asymmetric carbon atoms in the HSCIE reaction with spillover tritium in experiments. The regioselectivity and stereoselectivity of hydrogen isotope exchange in amino acids with spillover tritium can be predicted on the basis of ab initio calculations of interaction of this compound with a model acidic center, taking the H3O+ ion as an example.