THE FORMATION OF BETALAMIC ACID AND MUSCAFLAVIN BY RECOMBINANT DOPA-DIOXYGENASE FROM AMANITA

DOPA-dioxygenase from Amanita muscaria is known to catalyse the conver sion of 3-(3,4-dihydroxyphenyl)alanine (DOPA) to betalamic acid in the key reaction of betalain biosynthesis. In this work, we re-examined t he reactivity of DOPA-dioxygenase using a cDNA clone encoding active D OPA-dioxygenase the kinetic parameters of which were comparable to tho se of the native enzyme. Using L-DOPA as a substrate, the enzyme catal ysed the formation of two products. In addition to betalamic acid, the enzyme also catalysed the formation of muscaflavin, a compound that o ccurs naturally in A. muscaria and in mushrooms of the Hygrocybe famil y but not in the betalain-containing plants of the order Caryophyllale s. Muscaflavin arises by a 2,3-extradiol cleavage of DOPA, whereas bet alamic acid is the product of a 4,5-cleavage. Our results indicate tha t the recombinant enzyme has both 2,3- and 4,5-dioxygenase activity, a nd do not support the prevailing view that the two compounds are produ ced by two distinct enzymes. Copyright (C) 1997 Elsevier Science Ltd.