  1.13.12.17 | more |
StaP, a cytochrome P450 enzyme, catalyzes an aryl-aryl bond-forming reaction to give a six-ring indolocarbazole scaffold, as well as mediating decarboxylation and oxidation of the putative dicarboxypyrrole moiety. This action requires two to four cycles of net two-electron substrate oxidation at the catalytic heme center. StaP produces three distinct products, differing in oxidation level. For the production of K252c from chromopyrrolic acid, a net four-electron oxidation is required. The generation ofarcyriaflavin A from chromopyrrolic acid requires an overall eight-electron oxidation. StaP is thus unusual in the apparent lack of oxidative control it possesses over the outcome of its catalytic turnover. Control of the overall oxidation route is provided by a second enzyme StaC, which imparts the net effect of directing the oxidation level of the pyrrole-derived ring. While StaP in isolation gives three aglycone forms, StaP and StaC turn over chromopyrrolic acid to give only a single product, K252c. Similarly, RebC guides the turnover of chromopyrrolic acid toward the more highly oxidized maleimide-bearing aglycone, arcyriaflavin A |
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