What acute metabolic condition can be defined by the elevation of a yellow compound that occurs in normal catabolic pathway that breaks down heme in vertebrates?
Bilirubin Bilirubin (formerly referred to as haematoidin and discovered by Rudolf Virchow in 1847) is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged red blood cells. First the hemoglobin gets stripped of the heme molecule which thereafter passes through various processes of porphyrin catabolism, depending on the part of the body in which the breakdown occurs. For example, the molecules excreted in the urine differ from those in the faeces. The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin.
Adenosine kinase Adenosine kinase (AdK; EC 2.7.1.20) is an enzyme that catalyzes the transfer of gamma-phosphate from Adenosine triphosphate (ATP) to adenosine (Ado) leading to formation of Adenosine monophosphate (AMP). In addition to its well-studied role in controlling the cellular concentration of Ado, AdK also plays an important role in the maintenance of methylation reactions. All S-adenosylmethionine-dependent transmethylation reactions in cells lead to production of S-adenosylhomocysteine (SAH), which is cleaved by SAH hydrolase into Ado and homocysteine. The failure to efficiently remove these end products (Ado removed by phosphorylation by AdK) can result in buildup of SAH, which is a potent inhibitor of all transmethylation reactions. The disruption of AdK gene (-/-) in mice causes neonatal hepatic steatosis, a fatal condition characterized by rapid microvesicular fat infiltration, leading to early postnatal death. The liver was the main organ affected in these animals and in it the levels of adenine nucleotides were decreased, while those of SAH were elevated. Recently, missense mutations in the AdK gene in humans which result in AdK deficiency have also been shown to cause hypermethioninemia, encephalopathy and abnormal liver function.