Christova T, Diankova Z, Setchenska M
Institute of Biophysics, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Acta Physiol Pharmacol Bulg. 2000;25(1):9-17.
Heme oxygenase (HO) is a microsomal enzyme involved in the degradation of heme and biliverdin and carbon monoxide, the former being subsequently converted to bilirubin by the cytosolic biliverdin reductase. Two isoenzymes transcribed from separate genes have been characterized. The HO-2 isoform is constitutively expressed and is present in high concentration in the brain and testes. In contrast, the HO-1 isoform is ubiquitous, found in large quantities in liver and spleen and can be induced by its own substrate, heme and by a variety of stress-associated agents. Both HO-1 and HO-2 mRNA and protein have been detected in endothelial and smooth muscle cells of arterial and venous blood vessels. Carbon monoxide (CO) from HO catalysis has been identified as an endogenous biological messenger and recent studies suggest its important role in the circulation. Similarly to nitric oxide (NO), CO inhibits platelet aggregation and relaxes blood vessels by activating soluble guanylyl cyclase (sGC) and elevating intracellular levels of cyclic guanosine-3',5'-monophosphate (cGMP). CO is a powerful vasodilator and together with NO may serve as an important modulator of vascular cell function.
血红素加氧酶（HO）是一种微粒体酶，参与血红素、胆绿素和一氧化碳的降解，前者随后由胞质胆绿素还原酶转化为胆红素。已鉴定出由不同基因转录的两种同工酶。HO-2同工型是组成性表达的，在脑和睾丸中浓度很高。相比之下，HO-1同工型分布广泛，在肝脏和脾脏中大量存在，并且可被其自身底物血红素以及多种与应激相关的因子诱导。在动脉和静脉血管的内皮细胞和平滑肌细胞中均检测到了HO-1和HO-2的mRNA及蛋白质。HO催化产生的一氧化碳（CO）已被确定为一种内源性生物信使，最近的研究表明其在循环中起重要作用。与一氧化氮（NO）类似，CO通过激活可溶性鸟苷酸环化酶（sGC）并提高细胞内环鸟苷酸-3',5'-单磷酸（cGMP）的水平来抑制血小板聚集并舒张血管。CO是一种强大的血管舒张剂，可能与NO一起作为血管细胞功能的重要调节剂。
