Dopamine auto-oxidation

Garner CD, Nachtman JP. 1989. Manganese catalyzed auto-oxidation of dopamine to 6-hydroxydopamine in vitro. Chem. Biol. Interact. 69 345-51... 

Furthermore, the subsequent auto-oxidation of dopamine to the corresponding electrophiUc semiquinone and quinone analogues has also received considerable cognizance because these oxidationproducts are also cytotoxic in nature. Besides, Mn, is observed to catalyze oxidation of dopamine, and interestingly the resulting species viz., semiquinone and quinone have been duly implicated in the Mn-neurotoxicity. ... 

Kang CD, Jang JH, Kim KW, Lee HJ, Jeong CS, Kim CM, Kim SH, Chung BS. Activation of c-jun N-terminal kinase/stress-activated protein kinase and the decreased ratio of Bcl-2 to Bax are associated with the auto-oxidized dopamine-induced apoptosis in PC12 cells. Neurosci Lett 1998 256(1) 37 0. 

As a part of their research prograirune on the chemistry of melanins. Swan and his group in Newcastle have recently studied the tyrosine catalysed and auto-oxidation of dopamine (19) and DOPA (3) and a number of related compounds [57-60]. This group has also investigated the oxidation of 2,4,5-trihydroxyphenylethylamine (20) and synthesised a number of dimeric catecholamines 5,5, 6,6 -tetrahydroxy biphenyl-3,3 -ylenedi(ethyla-mine) (21) 5,5, 6,6 -tetrahydroxybiphenyl-2,2 -ylenedi(ethylamine) (22) 5,5, 6,6 -tetrahydroxybiphenyl-2,3 -ylenedi(ethylamine) (23) 2,3-bis(3,4-dihydroxyphenyl)butane-l,4-diamine (24) and 5,5, 6,6 -tetrahydroxybi-phenyl-3,3 -ylenedialanine (25) [58] and studied their tyrosinase catalysed oxidation, autoxidation, and oxidation with silver oxide, to melanins [59]. 

An enzyme system in rat brain oxidises DOPA to melanitic pigments and also adrenaline to adrenochrome [280, 281]. Serotonin is an effective inhibitor of both the auto-oxidation and enzymatic oxidation of dopamine [282]. The conversion of adrenaline to adrenochrome can either be accelerated or inhibited by serotonin, the nature of the effect being dependent on the relative concentrations of the amines in question [283]. An enzyme present in bovine uterine muscle oxidises adrenaline to adrenochrome and results in the formation of an actomyosin ATPase inhibitor [ 151,152,284,285], This enzyme has also recently been found in other animal tissues [286] and it has been demonstrated to be present in relatively high concentrations in muscles which are relaxed by adrenaline [286]. The oxidation of adrenaline to adrenochrome in the presence of rat parotid tissue in vitro has recently been reported [287]. 

Graham et al. (1978) conclude that 6-hydroxy-dopamine and 2,4,5-trihydroxyphenylalanine kill cells through the production of H2O2, 02 and HO, while for dopamine and dopa the reaction of qui-none oxidation products with nucleophiles probably also contributes to their cytotoxicity. 0-methyl-ated catecholamines are less susceptible to auto-xidation than their nonmethylated precursors (Miller etal. 1996). Melatonin, which has been shown to be a powerful, endogenous hydroxyl radical scavenger (Tan et al. 1993), is capable of scavenging free radicals produced during catecholamine autoxidation (Miller et al. 1996). 

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