Fig. 1.

Concentration-dependent inhibitory effects of heme proteins on fluorescein fluorescence. Catalase (A and B), reduced (oxy) hemoglobin (C), and methemoglobin (D) concentration dependently decreased fluorescence of 1 μM fluorescein, whereas albumin had no effect (E). A: experiment was started with 10 μM fluorescein, catalase was added at 0, 60, 90 and 120 min, while a second 10 μM fluorescein was added at 30 min (arrow). Each addition of catalase produced a proportional drop in fluorescence. (B–E) fluorescence values (left ordinate) are mean + SE, n = 4; percent decrease (right ordinate) was calculated from mean fluorescence values.