8-aminolevulinate synthase

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

Pyridoxine (B ) Pyridoxal-P (PLP) Aminotransferases (transaminase) AST (GOT), ALT (GPT) 8-Aminolevulinate synthase Protein catabolism Heme synthesis MCC isoniazid therapy Sideroblastic anemia Cheilosis or stomatitis (cracking or scaling of lip borders and corners of the mouth) Convulsions... 

Answer D. Sideroblastic anemia in a person being treated for tuberculosis (with isoni-azid) is most likely due to vitamin deficiency. 6-Aminolevulinate synthase, the first enzyme in heme synthesis requires vitamin Bj (pyridoxine). 

AMINOLEVULINATE DEHYDRATASE 5-AMINOLEVULINATE SYNTHASE AMINOMALONATE DECARBOXYLASE (R)-3-Amino-2-methylpropionate-pyruvate aminotransferase,... 

ALANYL-CoA AMMONIA LYASE 5-AMINOLEVULINATE SYNTHASE ARACHIDONYL-CoA SYNTHETASE... 

Bishop DF, Henderson AS, Astrin KH (1990) Human delta-aminolevulinate synthase assignment of the housekeeping gene to 3p21 and the erythroid-specific gene to the X chromosome. Genomics 7 207-214... 

Serine hydro xymethyltransferase Threonine aldolase 8-Aminolevulinate synthase Serine palmitoyltransferase 2-Amino-3-oxobutyrate-CoA ligase... 

Some mild forms of intermittent porphyria may go unrecognized. However, ingestion of drugs can precipitate an acute attack, probably by inducing excessive synthesis of 8-aminolevulinate synthase. Among compounds having this effect are hexachlo-robenzene and tetrachlorodibenzodioxin. 

The first step of porphyrin synthesis is the condensation of succinyl-CoA and glycine to form 8-aminolevulinate. The reaction takes place in mitochondria, where succinyl-CoA is available. The reaction is irreversible and requires pyridoxal phosphate and Mg2+. It is catalyzed by the enzyme 8-aminolevulinate synthase. 

Heme synthesis is controlled primarily by 8-aminolevulinate synthase (ALA synthase). There are two mechanisms of control, and each involves a process that affects the concentration of the enzyme. First, the half-life of ALA synthase, as shown by experiments in rat liver, is very short (60-70 min). Like many mitochondrial proteins, ALA synthase is encoded by nuclear genes, synthesized on cytoplasmic ribosomes, and the enzyme is translocated into the mitochondria. The second and main regulating factor is the inhibition of ALA synthase by hemin. Hemin differs from heme in that the Fe atom is in the Fe3+ oxidation state. Heme spontaneously oxidizes to hemin when there is no globin to form hemoglobin. Hemin serves a second function in the regulation of hemoglobin synthesis in reticulocytes. It controls the synthesis of globin. 

Excessive production of liver 5-aminolevulinate synthase causes two forms of congenital porphyria. These diseases are characterized by overproduction of porphyrins and excretion of large amounts of 5-aminolevulinate and porphobilinogen. Some ethnic groups have a high incidence of this disease, and in these people, acute attacks are brought on by barbiturates and other compounds that induce synthesis of the enzyme. 

Sideroblastic anemia 8-Aminolevulinate synthase (1 heme synthesis) 2.3.1.37... 

Cable, E.E., Cable, J.W., Bonkovsky, H.L. Depression of hepatic delta-aminolevulinate synthase by heme and metalloporphyrins relationship to inhibition of heme oxygenase. Hepatology 1993 18 119 — 127... 

When iron is low in the cell, the mRNA for ferritin is translated at a lesser rate (resulting in lesser amoimts of this protein in the cell). The goal here is to cut down on the excessive synthesis of our major iron storage protein, if no excess iron is available for storing. When iron is low in the cell, the mRNA for the transferrin receptor is translated more (creating more transferrin). When iron is low in the cell, the mRNA for 5-aminolevulinate synthase, an enz)mie in the heme biosynthetic pathway, is translated less. The overall goal here is to cut down on the wasteful synthesis of heme, if no iron is available for completing this cofactor. 

The a-oxoamine synthases family is a small group of fold-type I enzymes that catalyze Claisen condensations between amino acids and acyl-CoA thioesters (Figure 16). Members of this family are (1) 8-amino-7-oxononanoate (AON) synthase (AONS), which catalyzes the first committed step in the biosynthesis of biotine, (2) 5-aminolevulinate synthase (ALAS), responsible for the condensation between glycine and succinyl-CoA, which yields aminolevulinate, the universal precursor of tetrapyrrolic compounds, (3) serine palmitoyltransferase (SPT), which catalyzes the first reaction in sphingolipids synthesis, and (4) 2-amino-3-ketobutyrate CoA ligase (KBL), involved in the threonine degradation pathway. With the exception of the reaction catalyzed by KLB, all condensation reactions involve a decarboxylase step. 

Figure 2-1 Schematic representation of the heme biosynthetic pathway in mammalian cells. ALAS, S-aminolevulinate synthase PBGS, porphobiUnogen synthase PBGD, porphobilinogen deaminase Uro III synthase, uroporphyrinogen III synthase Uro III decarboxylase, uroporphyrinogen III decarboxylase CPO, coproporphyrinogen oxidase PPO, protoporphyrinogen oxidase FC, ferrochelatase.

---