Catalytic Differences between Flavohemoglobins of and .

The sole known heme enzyme of the parasitic protist is a flavohemoglobin (gFlHb) that acts as a nitric oxide dioxygenase (NOD) and protects the organism from the free radical nitric oxide. To learn more about the properties of this enzyme, we measured its nitric oxide dioxygenase, NADH oxidase, and cytochrome reductase activities and compared these to the activities of the flavohemoglobin (Hmp). The turnover number for the NOD activity of gFlHb (23 s) is about two-thirds of that of Hmp (34 s) at pH 6.