Succinyl-Coenzyme A Synthetase and its Role in δ-Aminolevulinic Acid Biosynthesis in Euglena gracilis

Abstract

Euglena gracilis cells synthesize the key tetrapyrrole precursor, 6-aminolevulinic acid (ALA), by two routes: plastid ALA is formed from glutamate via the transfer RNA-dependent five-carbon route, and ALA that serves as the precursor to mitochondnal hemes is formed by ALA synthase-catalyzed condensation of succinylcoenzyme A and glycine. The biosynthetic source of succinylcoenzyme A in Euglena is of interest because this species has been reported not to contain a-ketoglutarate dehydrogenase and not to use succinyl-coenzyme A as a tricarboxylic acid cycle intermediate. Instead, a-ketoglutarate is decarboxylated to form succinic semialdehyde, which is subsequently oxidized to form succinate. Desalted extract of Euglena cells catalyzed ALA formation in a reaction that required coenzyme A and GTP but did not require exogenous succinyl-coenzyme A synthetase. GTP could be replaced with ATP. Cell extract also catalyzed glycineand a-ketoglutarate-dependent ALA formation in a reaction that required coenzyme A and GTP, was stimulated by NADP+, and was inhibited by NAD . Succinyl-coenzyme A synthetase activity was detected in extracts of dark-and light-grown wild-type and nongreening mutant cells. In vitro succinyl-coenzyme A synthetase activity was at least 10-fold greater than ALA synthase activity. These results indicate that succinyl-coenzyme A synthetase is present in Euglena cells. Even though the enzyme may play no role in the transformation of a-ketoglutarate to succinate in the atypical tricarboxylic acid cycle, it catalyzes succinylcoenzyme A formation from succinate for use in the biosynthesis of ALA and possibly other products.lack the ability to form ALA from glutamate in vivo, and these strains rely on the ALA synthase route for all tetrapyrrole precursor biosynthesis (13,22).In the mitochondria of animals and yeasts, the ALA precursor, succinyl-CoA, is formed as the product of the aketoglutarate dehydrogenase reaction, a step of the tricarboxylic acid cycle. Euglena has been reported to have an atypical tricarboxylic acid cycle. The a-ketoglutarate dehydrogenase complex (EC 1.2.4.2, EC 2.3

Evolution of cyclizing 5-aminolevulinate synthases in the biosynthesis of actinomycete secondary metabolites: outcomes for genetic screening techniques

“…Some α-Proteobacteria, fungi, and animals form ALA through condensation of glycine and succinyl-CoA by hemA -encoded aminolevulinate synthase in so called C4 or Shemin pathway. Presence of both pathways in a single cell is extremely rare and their products are always temporally, spatially or functionally separated ( Weinstein and Beale, 1983 ; Mayer and Beale, 1992 ; Yang and Hoober, 1995 ). We recently reported one example in actinomycetes, where the C5 pathway is devoted to primary metabolism and the C4 strictly toward feeding biosynthesis of secondary metabolites containing the ALA-derived cyclic moiety, the C 5 N unit, 2-amino-3-hydroxycyclopent-2-enone ( Petříček et al, 2006 ; Supplementary Figure S1 ).…”

CARBON SOURCE DEPENDENCE OF THE RATIO OF δ‐AMINOLEVULINIC ACID BIOSYNTHESIS VIA THE C5 AND SHEMIN PATHWAYS IN EUGLENA GRACILIS (EUGLENOPHYCEAE)1

“…E. gracilis , which lacks 2‐oxoglutarate dehydrogenase, has an atypical TCA cycle, in which 2‐oxoglutaric acid is transformed to succinic acid via succinic semialdehyde, catalyzed by 2‐oxoglutarate decarboxylase and succinic semialdehyde dehydrogenase; in contrast, in the typical TCA cycle, 2‐oxoglutaric acid is transformed to succinic acid via succinyl CoA, as shown in Figure 1 (Shigeoka et al. 1986, 1992, Shigeoka and Nakano 1991, Mayer and Beale 1992, Green et al. 2000).…”

Regulation of the tetrapyrrole biosynthetic pathway leading to heme and chlorophyll in plants and cyanobacteria

“…ALS has not been identified in plants. Nonetheless, in Euglena gracilis (Mayer and Beale 1992) and probably Scenedesmus (Drechsler‐Thielmann et al. 1993) aminolevulinic acid can be synthesized via both the Shemin and the C 5 pathways.…”