Radiation chemical methods were used to investigate the reactions of glycine anions, H2NCH2CO2-(Gly(-)), with (OH)-O-., (CH3)(2)(COH)-O-., and (CH3)-C-. radicals. A major and most significant product from all of these processes is CO2. Pulse-radiolysis revealed that the initial step in the (OH)-O-.-induced mechanism is oxidation of the amino group, producing (+H2N.)-CH2-CO2- and HN.-CH2-CO2- with yields of 63% and 37%, respectively. The amino radical cation, (+H2N.)-CH2-CO2-, suffers fast (less than or equal to 100 ns) fragmentation into CO2 + (CH2NH2)-C-.. The other primary radical, HN.-CH2-CO2-, can also be converted into the decarboxylating (+H2N.)-CH2-CO2-by reaction with proton donors such as phosphate (H2PO4-/k = 7.4 x 10(7) M-1 s(-1), and HPO42-/k = 2.5 x 10(5) M-1 s(-1)) or the glycine zwitterion, Gly(+/-) (k = 3.9 x 10(5) M-1 s(-1)), but only on a much longer (typically mu s to ms) time scale (k approximate to 4 x 10(5) M-1 s(-1)). Competitively, the HN.-CH2-CO2- transforms into a carbon-centered radical H2N-(CH)-H-.-CO2- either by an intramolecular 1,2-H-atom shift (k = (1.2 +/- 1.0) x 10(3) s(-1)) or by bimolecular reaction with Gly(-) (k = (3.0 +/- 0.2) x 10(4) M-1 s(-1)). Both C-centered radicals, H2N-(CH)-H-.-CO2- and (CH2NH2)-C-., are reductants as verified through their reactions with Fe(CN)(6)(3-) and methyl viologen (MV2+) in pulse-radiolysis experiments (k approximate to 4 x 10(9) M-1 s(-1)). The eventual complete transformation of all primary radicals into H2N-(CH)-H-.-CO2- and (CH2NH2)-C-. was further substantiated by gamma-radiolytic reduction of Fe(CN)(6)(3-). In the presence of suitable electron donors, the HN.-CH2-CO2- radical acts as an oxidant. This was demonstrated through its reaction with hydroquinone (k = (7.4 +/- 0.5) x 10(7) M-1 s(-1)). Although the C-centered H2N-(CH)-H-.-CO2-radical is not generated in a direct H-atom abstraction by (OH)-O-., this radical appears to be the exclusive product in the reaction of Gly(-) with (CH3)(2)(COH)-O-., (CH2NH2)-C-., and (CH3)-C-. (k approximate to 10(2) M-1 s(-1)). A most significant finding is that H2N-(CH)-H-.-CO2- can be converted into the decarboxylating N-centered radical cation (+H2N.)-CH2-CO2- by reaction with proton donors such as Gly(+/-) (k approximate to 3 x 10(3) M-1 s(-1)) or phosphate and thus also becomes a source of CO2. The (CH2NH2)-C-.-induced route establishes, in fact, a chain mechanism which could be proven through dose rate effect experiments and suppression of the chain upon addition of Fe(CN)(6)(3-) or MV2+ as a scavenger for the reducing precursor radicals. The possible initiation of amino acid decarboxylation by C-centered radicals and the assistance of proton donors at various stages within the overall mechanism are considered to be of general significance and interest in chemical and biological systems.