P450-only Systems
Nitric oxide reductase (P450nor) is a P450 enzyme involved in denitrification in several fungal species. The best-characterized P450nor is CYP55 from Fusarium oxysporum. This enzyme does not have monooxygenase activity but is able to reduce nitric oxide (NO·) to form nitrous oxide (N2O) directly using NAD(P)H as electron donor:
Fatty acid β-hydroxylase P450BSβ from Bacillus subtilis (CYP152A1) and fatty acid α-hydroxylase P450SPα from Pseudomonas paucimobilis (CYP152B1) catalyse the hydroxylation reaction of long-chain fatty acids using hydrogen peroxide (H2O2) as an oxidant. These enzymes do not require any reduction system for catalysis. Allene oxide synthase (CYP74A; EC 4.2.1.92), fatty acid hydroperoxide lyase (CYP74B), prostacyclin synthase (CYP8; EC 5.3.99.4) and thromboxane synthase (CYP5; EC 5.3.99.5) are examples of P450 enzymes that do not require a reductase or molecular oxygen for their catalytic activity. Substrates for all these enzymes are fatty acid derivatives containing partially reduced dioxygen (either hydroperoxy or epidioxy groups).
NAD(P)H
NO·
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