ho-1

Heme Oxygenase 1 (HO-1) is an enzyme in endoplasmic reticulum that belongs to the heme oxygenase family. HO-1 cleaves the heme ring at the alpha methene bridge to form Biliverdin. Biliverdin is subsequently converted to Bilirubin by Biliverdin reductase. In physiological state, the highest activity of HO-1 is found in the spleen, where senescent erythrocytes are sequestrated and destroyed. HO-1 activity is highly inducible by its substrate heme and by various non-heme substances such as heavy metals, bromobenzene, endotoxin, oxidizing agents and UVA. HO-1 is involved in the regulation of cardiovascular function and response to a variety of stressors. Defects in HO-1 are the cause of Heme Oxygenase 1 deficiency, resulting in marked erythrocyte fragmentation and intravascular hemolysis, coagulation abnormalities, endothelial damage, and iron deposition in renal and hepatic tissues.

Biliverdin reductase (hBVR) is a serine threonine kinase that catalyzes reduction of the heme oxygenase (HO) activity product, biliverdin, to bilirubin. BVR consists of an N-terminal dinucleotide-binding domain (Rossmann-fold) and a C-terminal domain that contains a six-stranded β-sheet that is flanked on one face by several α-helices. The C-terminal and N-terminal domains interact extensively, forming the active site cleft at their interface. Biliverdin reductase (BVR) catalyzes the last step in heme degradation by reducing the γ-methene bridge of the open tetrapyrrole, biliverdin IXα, to bilirubin with the concomitant oxidation of a β-nicotinamide adenine dinucleotide (NADH) or β-nicotinamide adenine dinucleotide phosphate (NADPH) cofactor. It is now recognized that human BVR (hBVR) is a dual-specificity kinase (Ser Thr and Tyr) upstream activator of the insulin insulin growth factor-1 (IGF-1) and mitogen-activated protein kinase (MAPK) signaling pathways. Human BVR (hBVR) is essential for MAPK-extracellular signal-regulated kinase (ERK)1 2 (MEK)-eukaryotic-like protein kinase (Elk) signaling and has been identified as the cytoplasm-nuclear heme transporter of ERK1 2 and hematin, the key components of stress-responsive gene expression.