Biliverdin reductase

About: Biliverdin reductase is a research topic. Over the lifetime, 571 publications have been published within this topic receiving 37304 citations. The topic is also known as: bilirubin:NAD(P)+ oxidoreductase.

Bilirubin is an antioxidant of possible physiological importance

Abstract: Bilirubin, the end product of heme catabolism in mammals, is generally regarded as a potentially cytotoxic, lipid-soluble waste product that needs to be excreted. However, it is here that bilirubin, at micromolar concentrations in vitro, efficiently scavenges peroxyl radicals generated chemically in either homogeneous solution or multilamellar liposomes. The antioxidant activity of bilirubin increases as the experimental concentration of oxygen is decreased from 20% (that of normal air) to 2% (physiologically relevant concentration). Furthermore, under 2% oxygen, in liposomes, bilirubin suppresses the oxidation more than alpha-tocopherol, which is regarded as the best antioxidant of lipid peroxidation. The data support the idea of a "beneficial" role for bilirubin as a physiological, chain-breaking antioxidant.

THE HEME OXYGENASE SYSTEM:A Regulator of Second Messenger Gases

Abstract: The heme oxygenase (HO) system consists of two forms identified to date: the oxidative stress-inducible protein HO-1 (HSP32) and the constitutive isozyme HO-2. These proteins, which are different gene products, have little in common in primary structure, regulation, or tissue distribution. Both, however, catalyze oxidation of heme to biologically active molecules: iron, a gene regulator; biliverdin, an antioxidant; and carbon monoxide, a heme ligand. Finding the impressive heme-degrading activity of brain led to the suggestion that "HO in brain has functions aside from heme degradation" and to subsequent exploration of carbon monoxide as a promising and potentially significant messenger molecule. There is much parallelism between the biological actions and functions of the CO- and NO-generating systems; and their regulation is intimately linked. This review highlights the current information on molecular and biochemical properties of HO-1 and HO-2 and addresses the possible mechanisms for mutual regulatory interactions between the CO- and NO-generating systems.

Heme oxygenase: function, multiplicity, regulatory mechanisms, and clinical applications.

Abstract: In biological systems oxidation of heme is carried out by two isozymes of the microsomal heme oxygenase, HO-1 and HO-2. HO-1 is the commonly known heme oxygenase, the activity of which can be induced by up to 100-fold in response to a wide variety of stimuli (metals, heme, hormones, etc.). HO-2 was only recently discovered, and the isozyme appears to be uninducible. The two forms are products of two different genes and differ in their tissue expression. The primary structure of HO-1 and an HO-2 fragment of 91 amino acid residues show only 58% homology, but share a region with 100% secondary structure homology. This region is believed to be the catalytic site. Most likely, HO-1 gene is regulated in the same manner as metallothione in the gene. HO-1 has a heat shock regulatory element, and possibly many promoter elements, which bind to respective inducers and cause transcription of the gene. In vivo induction of HO-1 activity in the liver is accompanied by decreases in the total P-450 levels and, in a reconstituted system, cytochrome P-450b heme can be quantitatively converted to biliverdin by HO-1 and HO-2. The enzyme activity is inhibited in vivo for extended periods subsequent to binding of Zn- and Sn- protoporphyrins. This property appears useful for the suppression of bilirubin production. The metalloporphyrins, however, are not innocuous and cause major disruptions in cellular metabolism. In this review recent findings on heme oxygenase are highlighted.