Dopachrome conversion factor functions as an isomerase

Abstract

Dopachrome conversion factor is an enzymatic activity associated with the pigmentary system which catalyzes the conversion of dopachrome, an intermediate in melanin biosynthesis, to dihydroxyindole-2-carboxylic acid (DHICA). To date, the mechanism of action of DCF has been unknown because all previous assays have employed a dopachrome substrate contaminated with L-dopa. It has therefore not been possible to determine whether L-dopa acts as a hydrogen donor in the reaction or whether the formation of DHICA occurs through an isomerization of dopachrome. In this study it is shown that DCF catalyzes the conversion of dopachrome to DHICA equally well in the presence or absence of L-dopa. The DCF-mediated reaction thus appears to be an isomeric rearrangement of hydrogen ions from one portion of the dopachrome molecule to another. The results indicate that the name "dopachrome isomerase" appropriately describes the function of DCF.