Hydroxyl Radical Induced Decarboxylation and Deamination of 2-Methylalanine Catalyzed by Copper Ions

Using the pulse radiolysis technique, the rate constants of the reactions of CH₂C(CH₃)(NH₃⁺)COO^- (the radical derived via H-abstraction from 2-methylalanine) with Cu²⁺aq and Cu⁺_aq to form unstable intermediates with a copper-carbon -bond have been determined to be (1.3 ± 0.3) × 10⁷ and (1.3 ± 0.2) × 10⁹ M^-1 s^-1, respectively. In the case of cupric ions, the transient decomposes via a β-carboxyl elimination reaction yielding Cu⁺ _aq, CH₃COCH₃, and CO₂, whereas in the case of cuprous ions it decomposes via a β-amine elimination reaction yielding Cu²⁺ _aq, CH₂=C(CH₃)COO^-, and NH₃. A reaction mechanism for aliphatic radical induced amino acid damage catalyzed by copper ions in different oxidation states is suggested. This mechanism describes a plausible new pathway for biological damage induced by free radicals.