Biomaterial Database

Vitamin B6 metabolism by human liver. 1990

A H Merrill, and J M Henderson

Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.

The B6 vitamers (pyridoxine, pyridoxamine, and pyridoxal) are primarily metabolized in liver to pyridoxal 5'-phosphate (PLP) and the deadend catabolite 4-pyridoxic acid. We have built on the elegant early work of Snell and others to describe the activities of the human liver enzymes responsible for vitamin B6 metabolism and to develop a model of the relative rates of these interconversions in vivo. This model is consistent with changes in plasma B6 after a load, the clearance of different vitamers (e.g., pyridoxine versus pyridoxal), and with the low plasma PLP in patients with cirrhosis. Because cirrhotics were found to be capable of PLP synthesis, we have used oral supplementation with pyridoxine to restore plasma PLP to the normal range, and have evaluated the effects of this intervention on amino acid metabolism. No significant differences were observed in plasma or urinary clearance of methionine (or cystathionine) after an oral load, nor in amino acid clearance from circulation after a protein load for cirrhotic patients before and after restoration of normal plasma PLP. Hence, the abnormal metabolism of vitamin B6 does not appear to be an important factor in the deranged amino acid metabolism in this disease. Nonetheless, this approach may be generally useful in assessing the importance of PLP in other abnormalities.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008099	Liver	A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.	Livers
D008103	Liver Cirrhosis	Liver disease in which the normal microcirculation, the gross vascular anatomy, and the hepatic architecture have been variably destroyed and altered with fibrous septa surrounding regenerated or regenerating parenchymal nodules.	Cirrhosis, Liver,Fibrosis, Liver,Hepatic Cirrhosis,Liver Fibrosis,Cirrhosis, Hepatic
D011732	Pyridoxal Phosphate	This is the active form of VITAMIN B 6 serving as a coenzyme for synthesis of amino acids, neurotransmitters (serotonin, norepinephrine), sphingolipids, aminolevulinic acid. During transamination of amino acids, pyridoxal phosphate is transiently converted into pyridoxamine phosphate (PYRIDOXAMINE).	Pyridoxal 5-Phosphate,Pyridoxal-P,Phosphate, Pyridoxal,Pyridoxal 5 Phosphate,Pyridoxal P
D011735	Pyridoxic Acid	The catabolic product of most of VITAMIN B 6; (PYRIDOXINE; PYRIDOXAL; and PYRIDOXAMINE) which is excreted in the urine.	Pyridoxinecarboxylic Acid,4-Pyridoxic Acid,4-Pyridoxinic Acid,4-Pyridoxylic Acid,4 Pyridoxic Acid,4 Pyridoxinic Acid,4 Pyridoxylic Acid
D011736	Pyridoxine	The 4-methanol form of VITAMIN B 6 which is converted to PYRIDOXAL PHOSPHATE which is a coenzyme for synthesis of amino acids, neurotransmitters (serotonin, norepinephrine), sphingolipids, aminolevulinic acid. Although pyridoxine and Vitamin B 6 are still frequently used as synonyms, especially by medical researchers, this practice is erroneous and sometimes misleading (EE Snell; Ann NY Acad Sci, vol 585 pg 1, 1990).	Pyridoxin,Pyridoxine Hydrochloride,Pyridoxol,Pyridoxol Hydrochloride,Rodex
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000596	Amino Acids	Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.	Amino Acid,Acid, Amino,Acids, Amino