The Production of Carbon Monoxide from Hemoglobin In Vivo*

Abstract

Summary. Dogs anesthetized with pentobarbital were shown to produce carbon monoxide at an average rate of 0.21 + (SD) 0.05 ml per hour. After intravenous injection of erythrocytes damaged by incubation with N-ethylmaleimide, CO was produced in excess of base-line production for 3 to 4 hours with an average yield of 0.89 + (SE) 0.046 umole of carbon monoxide to 1 Mmole of heme degraded.After intravenous injection of N-ethylmaleimide (NEM)-treated erythrocytes containing hemoglobin labeled with 14carbon, 14CO was produced. Its specific activity was approximately one-eighth that of the injected heme. It was also produced after intravenous injection of solutions of hemoglobin-14C and of reconstituted methemoglobin containing hemin-14C, but not after injections of methemoglobin containing globin-14C. The average yields of 14CO from metabolized heme in the experiments with damaged erythrocytes and hemoglobin solutions were 89 + (SE) 4.6 and 97 + (SE) 17.0%, respectively. These results demonstrate that the CO produced during hemoglobin degradation arises from the heme moiety.The yield of 14CO after injection of hemoglobin-14C solutions decreased significantly to values of 35 and 42% in two experiments when exogenous CO was added to the body stores, resulting in blood carboxyhemoglobin levels of 11.3 and 13.2% saturation. This finding suggests that oxidative metabolism is required during catabolism of hemoglobin to CO and that carboxyhemoglobin levels in this range are sufficient to cause inhibition.After intravenous injection of either hemin-14C or protoporphyrin-14C, 14CO was also produced. After injection of protoporphyrin-14C labeled bilirubin was isolated from gall bladder bile, and labeled hemin was isolated from the liver. It is thus very likely that protoporphyrin is converted to heme before the formation of CO.There was a large difference between the maximal rates of catabolism of hemoglobin to CO observed after injection of damaged erythrocytes and hemoglobin solutions. The limiting parameters in these processes are not yet clear.

Formation of Carbon Monoxide and Bile Pigment in Red and Blue-Green Algae

“…This conclusion is consistent with the data on specific radioactivity ratios of phycocyanobilin and CO made from ALA-5-4C in cells of the green alga, Cyanidium caldarium (31). It has been observed that metal-free protoporphyrin IX is converted slowly and inefficiently to bile pigment in mammals (7), in contrast to hemoglobin or hematin which are rapidly and quantitatively converted to CO and bilirubin in vivo (2,11) and in vitro (26,27). This suggests that phycocyanobilin and phycoerythrobilin may also arise from catabolism of a metalloporphyrin precursor rather than from metal-free protoporphyrin IX.…”

Carbon Monoxide Production Associated with Ineffective Erythropoiesis*

“…Conversion of free hemin and free protoporphyrin to bile pigment has been demonstrated in experimental animals (49)(50)(51)(52), and we have similarly recovered 14CO after the injection of hemin-14C and protoporphyrin-14C into dogs (21). In addition, recent findings in several laboratories (6-9) have implicated the liver in the production of bilirubin de novo from glycine and delta amino levulinic acid, and have suggested that turnover of heme compounds in the liver may give rise to a significant fraction of the early labeled peak of stercobilin.…”

“…CO has been shown to be a normal end product of human metabolism (18,19) and its rate of production (Vco) in normal subjects is consistent with the concept that hemoglobin catabolism provides its major source. CO release during heme degradation has been demonstrated using in vitro models (20), and isotopic studies have shown that CO most probably arises from the alpha methine bridge carbon atom of the porphyrin ring in the degradation of heme in vivo (21). Studies of CO metabolism in normal subjects injected with damaged erythrocytes and in patients with hemolytic anemia have shown a close correlation between Vco and the rate of circulating heme catabolism (22,23).…”

“…5 Toluene-"C was used as internal standard; counting efficien-y was 30-40%. Carbon monoxide was collected with a washout procedure similar to that previously described (21), by increasing the 02 partial pressure in the rebreathing system to 80-90% and collecting expired air in a large rubber bag (100 liter capacity). Up to 50% of the total body CO pool could be collected over a 40 min period.…”

“…to compare these two methods with each other and with a third, previously described method (21) utilizing an ionization chamber to measure radioactivity in the rebreathing system gas. As shown in Table II, there was good agreement between these different methods for determining "CO specific activity.…”