Most CO excreted by mammals results from the degradation of heme. However, some CO is derived from other sources. We studied the Fe2+-initiated peroxidation of tissue homogenate fractions that yield a number of products, including thiobarbituric acid reactive substances (TBARS) and CO. Post-mitochondrial rat tissue supernatants were incubated in the dark with 100μM ascorbate (Asc) and 6 μM Fe2+ for 30 min at 37°C in septum-sealed vials. Control reactions contained 100 μM butylated hydroxytoluene (BHT). CO in the headspace was determined by GC and TBARS in the liquid phase was measured spectrophotometrically. Reaction mixture composition and product formation (n=3, pmoles CO/4 mg fresh weight) are as follows (mean ± SD): Table When brain homogenate was fractionated, CO production occurred with mitochondria (86±27) and microsomes(100±26), but not with the soluble fraction (1±1). Supernatants from brain (242±18), kidney (198±20), spinal cord(159±23), lung (22±5), and spleen (21±4) produced CO, but not those from blood (8±5), intestine (3±2), liver (2±2), nor heart (1±1). Bilirubin inhibited brain peroxidation completely at 3 mg/dL. Iron chelators, such as desferrioxamine, completely suppress CO and TBARS production. We conclude that: CO is a product of Fe2+-initiated peroxidation in vitro, in parallel with TBARS; CO production occurs in membranes only. We speculate that tissue supernatants that do not produce CO are protected from oxidation by endogenous antioxidants, such as bilirubin.

Table 1
Full size table