New Classification System for Oxygenase Components Involved in Ring-Hydroxylating Oxygenations

Batie et al. [Chemistry and Biochemistry of Flavoenzymes, 3, 543-556(1991)] proposed a classification system for ring-hydroxylating oxygenases in which the oxygenases are grouped into three classes in terms of the number of constituent components and the nature of th redox centers. But in recent years, many ring-hydroxylating oxygenases have been newly identified and characterized, and found dificult to classify into these three classes. Typical examples are carbazole 1,9a-dioxygenase and 2-oxo-1,2-dihydroquinoline 8-monooxygenase, which have been classified into class III and class IB, respectively, from biochemical characteristics. However, a phylogenetic study showed that the terminal oxygenases of both are closely related to class IA. Because this discrepancy derived from counting all the components together, here we proposed a new scheme based on the homology of the amino acid sequences of the α subunits of the terminal oxygenase components. This new scheme strongly reflects the actual phylogenetic a...