<jats:title>Abstract</jats:title><jats:p>An enzyme is extracted from the red peel of <jats:italic>Amanita muscaria</jats:italic> which cleaves the C(2)–C(3) and the C(4)–C(5) bond of the aromatic ring of <jats:sc>L</jats:sc>‐dopa (<jats:bold>1</jats:bold>) to form a mixture of 4,5‐secodopa (= salt of 6‐amino‐2‐hydroxy‐4‐(2′‐oxoethylidene)hept‐2‐enedioic acid; <jats:bold>2</jats:bold>) and 2,3‐secodopa ( = salt of 7‐amino‐5‐formyl‐2‐hydroxyocta‐2,4‐dienedioic acid; <jats:bold>3</jats:bold>), two hitherto hypothetical biosynthetic intermediates (see <jats:italic>Scheme</jats:italic>). Though isolation of these products has not been possible, structural evidence is inferred from reaction products, kinetics, and spectroscopical characteristics in comparison with known compounds. Secodopas <jats:bold>2</jats:bold> and <jats:bold>3</jats:bold> are characterized in dilute solution by HPLC and UV/VIS spectroscopy (anions; λ<jats:sub>max</jats:sub> 424 and 414 nm, resp., ϵ<jats:sub>420</jats:sub> = 25500; on acidification, shift to 380 and 372 nm, resp.). They cyclize without enzyme catalysis, optimally at pH 4.5–5; <jats:bold>3</jats:bold> produces muscaflavin (<jats:bold>5</jats:bold>) and <jats:bold>2</jats:bold> betalamic acid (<jats:bold>4</jats:bold>). The products arc identified by direct comparison with authentic samples in HPLC, by <jats:sup>1</jats:sup>H‐NMR of <jats:bold>5</jats:bold>, and by condensation of <jats:bold>4</jats:bold> with <jats:sc>L</jats:sc>‐proline to form the well known betalain indicaxanthin (<jats:bold>7</jats:bold>). The enzymatic conversion of <jats:sc>L</jats:sc>‐dopa (<jats:bold>1</jats:bold>) <jats:italic>via</jats:italic> <jats:bold>2</jats:bold> to betalamic acid (<jats:bold>4</jats:bold>; (<jats:italic>S</jats:italic>)) and its condensation with <jats:sc>L</jats:sc>‐proline leads to pure natural indicaxanthin (<jats:bold>7</jats:bold>; (2<jats:italic>S</jats:italic>,11<jats:italic>5</jats:italic>)); correspondingly, the enzymatic conversion of <jats:sc>D</jats:sc>‐dopa to (<jats:italic>R</jats:italic>)‐betalamic acid and its condensation with <jats:sc>L</jats:sc>‐proline produces isoindicaxanthin ((2<jats:italic>S</jats:italic>,11<jats:italic>R</jats:italic>)) which is unknown in nature. Particularly relevant is the fact that the same enzyme cleaves pyrocatechol to produce a solution of the enolate form of the known 2‐hydroxy‐6‐oxohexa‐2,4‐dienoate (secopyrocatechol; <jats:bold>9</jats:bold>; see <jats:italic>Fig. 5</jats:italic>). Dissociation constants of the corresponding enolic functions in the cleavage products are determined by spectrometric titration and compared to those of known systems.