(A) Rate of ¹²⁵I-Hb clearance from the plasma. ¹²⁵I-Hb (0.1 mg/10 g body weight; 7 × 10⁵ cpm/μg Hb) was injected intravenously through the tail vein of anesthetized 5-to 6-week-old mice as described in the Materials and Methods. Two mice of each genotype were used and each data point represent the average from the two mice. (B and C) Rates of free plasma Hb accumulation and clearance during phenylhydrazine treatment. Different degrees of hemolysis were induced in 5- to 6-week-old mice by treating them with either two IP injections of 0.5 mg/10 g body weight spaced 8 hours apart on day 1 (B) or one IP injection of 2 mg/10 g body weight on day 1 (C). (Upper panels) plasma Hb level; (lower panels) mean hematocrit ± standard deviation (SD). A total of 7 −/− and 5 +/+ mice were used for (C), but two −/− mice died during the course of the experiment. In both studies (B and C), the levels of plasma Hb between +/+ and −/− mice at each time point were not significantly different by ANOVA (P = .35 and P = .89 for [B] and [C], respectively).