LIPID-PEROXIDATION INHIBITED BY MONOAMINES

We investigated the inhibition of lipid peroxidation by monoamines. We found that monoamines, including dopa, dopamine, adrenaline and serot onin, strongly inhibited lipid peroxidation induced by 2,2'-azobis-(2- amidinopropane)-dihydrochroride (AAPH). In contrast, lipid peroxidatio n induced by 2,2'-azobis-(2,4-dimethylvaleronitrile) was not effective ly inhibited by the monoamines. Degradation of R-phycoerythrin induced by AAPH was strongly prevented by these monoamines, suggesting that m onoamines scavenge peroxyl radicals in the buffer and on the surface o f membrane lipid layers. Methoxy derivatives of dihydroxyphenylacetic acid and 5-methoxytryptophan produced little inhibition of lipid perox idation induced by AAPH, suggesting that hydroxy groups of monoamines donate protons to peroxyl radicals to prevent lipid peroxidation. Howe ver, the monoamines did not sharply inhibit lipid peroxidation induced by ascorbate-ADP-Fe3+ and t-butylhydroperoxide-Fe2+. Lipid peroxidati on predominantly proceeding by peroxyl radicals in these reaction syst ems seems unlikely.