The formation of betalamic acid and muscaflavin by recombinant DOPA- dioxygenase from Amanita

Article abstract of DOI:10.1016/S0031-9422(96)00625-5

DOPA-dioxygenase from Amanita muscaria is known to catalyse the conversion of 3-(3,4-dihydroxyphenyl)alanine (DOPA) to betalamic acid in the key reaction of betalain biosynthesis. In this work, we re-examined the reactivity of DOPA-dioxygenase using a cDNA clone encoding active DOPA- dioxygenase the kinetic parameters of which were comparable to those of the native enzyme. Using L-DOPA as a substrate, the enzyme catalysed the formation of two products. In addition to betalamic acid, the enzyme also catalysed the formation of muscaflavin, a compound that occurs naturally in A. muscaria and in mushrooms of the Hygrocybe family but not in the betalain- containing plants of the order Caryophyllales. Muscaflavin arises by a 2,3- extradiol cleavage of DOPA, whereas betalamic acid is the product of a 4,5- cleavage. Our results indicate that the recombinant enzyme has both 2,3- and 4,5-dioxygenase activity, and do not support the prevailing view that the two compounds are produced by two distinct enzymes.