Figure 2.

Potentiation of iNOS activity by nonheme iron. The upper panel compares the amount of citrulline formed by various amounts of iNOS after 2.5 min in the presence (○) and absence (•) of 20 μM FeCl₂ at 25°C. Saturation of the effect in the presence of nonheme iron reflects the presumed depletion of oxygen. The lower panel is an activity time course of 500 nM iNOS in the presence (○) and absence (•) of 20 μM FeCl₂ when assayed at 0°C. This panel demonstrates that the addition of nonheme iron may have two stimulatory effects, one on the initial rate of product formation, and one on the steady-state rate.