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 sigma-bond have been determined to be (1.3 +/- 0.3) x 10(7) and (1.3 +/- 0.2) x 10(9) M-1 s-1, respectively. In the case of cupric ions, the transient decomposes via a beta-carboxyl elimination reaction yielding Cu+aq, CH3COCH3, and CO2, whereas in the case of cuprous ions it decomposes via a beta-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.