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SummaryThe auto-oxidation of adrenaline in concentrations of M/500 to M/10,000 and at pH 6-8 starts after a time lag that is dependent on the conditions but independent of the adrenaline concentration. This is followed by a short period of rapid acceleration of the oxidation rate and then by a period of steady oxidation of constant rate for several hours, proportional to the adrenaline concentration. The solutions are red, later orange to brown, melanin is formed, and the oxygen uptakes, six to seven atoms for one molecule of adrenaline, indicate destructive oxidation beyond opening of the ring structure.It is suggested that during the time lag the oxidation of adrenaline is started by traces of metallic ions (Fe and Cu) present, adrenochrome being formed in the process and further catalysing the reaction. The acceleration of the oxidation rate and the onset of destructive oxidation are due to the formation of more readily oxidizable compounds of indoxyl structure, the reaction probably involving a free radical mechanism. The later, constant oxidation proceeds over the quinonoid redox systems of adrenochrome and oxocadrenochrome that are established during the period of acceleration. At this stage the reaction mixture consists of unreacted adrenaline, the quinonoid systems, and of further oxidation products, which act as hydrogen donors towards the quinones. The regulation of the oxidation rate is ascribed to the effect of the hydrogen transfers on the redox potential of the quinonoid systems and possibly to the inhibiting influence of later oxidation products. Finally the ring structures are consumed and, apart from condensation products like melanin, the reaction mixture consists. of late oxidation products which without the action of redox systems, undergo further atmospheric oxidation. Tentative formulations of the earlier steps of adrenaline oxidation are proposed.The influence of catalysts, heavy metal ions (Fe and Cu, also haematin and methaemoglobin), and adrenochrome is confined to the initial stages of the reaction sequence; they shorten the time lag and cause a transient period of more rapid oxygen uptake, the duration of which depends on their concentration. In catalytic amounts they do not appreciably affect the rate of the final oxidation.The auto-oxidation of adrenochrome begins after a time lag and shows a period of more rapid oxidation before the final stefldy oxidation rate is established.Oxidizing red adrenaline solutions or adrenochrome solutions form strongly fluorescent colourless to yellow solutions on reduction imd on addition of free alkali with or without the admission of air. It is suggested that, depending on the conditions, leuco-adrenochrome or N-methyl-5 : 6-dihydroxy-indoxyl, but usually mixtures of both compounds are formed. If at lower pH (7-8.5) adrenaline is allowed to oxidize in the presence of reducing agents ( sulphite, " Department of Physiology, University of Melbourne. 304 E. M. TRAUTNER AND T. R. BRADLEY amino acids, etc.) almost colourless fluorescent solutions are for...

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SummaryThe continuous deamination of certain amino acids by the system catecholpolyphenolase takes place through intensely coloured intermediate compounds. These intermediates are formed by the combination of equimolecular proportions of o-quinone with amino acids or secondary amines. They are presented as structural homologues of adrenochrome or hallachrome and probably of Szent-Gyorgyi's tyrin (1925).It is suggested that the continuous deamination is brought about through condensation of the colour compound with one further molecule of ~ suitable amino acid and rearrangement and hydrolysis into keto acid and substituted amino phenol. It is supposed that the latter is re-oxidized with liberation of ammQnia and regeneration of the o-quinonoid colour compound. A formulation of the chemical mechanism is tentatively proposed and individual steps of the reaction are compared with observations made in the oxidation of amino acids by other polyketo compounds . like alloxan and isatin. The conditiOns and limitations of the reaction are discussed.