Biosynthesis of δ-Aminolevulinic Acid from Glutamate in Agmenellum quadruplicatum

Abstract

5-Aminolevulinic acid accumulated in the culture medium when Agmeneflum quadplicatum strain PR-6 was incubated in the presence of levulinic acid, a competitive inhibitor of 8-aminolevulinic acid dehydratase, and specifically labeled glutamate and glycine. The 8-aminolevulinic acid was purified using Dowex 50W-X8 and cleaved by periodate to yield succinic acid and formaldehyde. The distribution of radioactivity in the two fragments suggested that in blue-green algae the carbon skeleton of 8-aminolevulinic acid is derived directly from glutamate. However the possibility of the pathway of 8-aminolevulinic acid synthesis, from glycine and succinyl-coenzyme A also functioning in blue-green algae was not eliminated as uptake of glycine was minimal.&-Aminolevulinic acid is the first identified biosynthetic intermediate that is unique to the tetrapyrrole pathway. ALA2 is the precursor of heme in animals (16) and bacteria (9); of Chl in bacteria (6) and plants (8); and of the phycobilins in red algae (19). In many organisms ALA is formed by the condensation of glycine and succinyl-CoA, catalyzed by ALA synthetase, a pyridoxal-requiring enzyme. The enzymatic activity was first demonstrated in photosynthetic bacteria (12) and chicken erythrocytes (7). ALA synthetase has since been reported in yeast, bacteria, and a number of animal tissues. However, workers have been unable to demonstrate conclusively ALA synthetase activity in green plants and green algae (2).In studies in which cucumber cotyledons (3), bean and barley leaves (4), maize leaves (15), and the unicellular rhodophyte Cyanidium caldarium (10) were incubated in the presence of levulinic acid and labeled compounds; glutamate, a-ketoglutarate, and glutamine were found to donate label to the ALA that accumulated, much more effectively than glycine. Furthermore, from the specific pattern of incorporation of label into ALA, it appears that ALA is formed from the intact carbon skeleton of glutamate in a manner incompatible with the ALA synthetase route (1,5,10,15).Herein, we report the labeling of ALA from specifically labeled glutamate by a blue-green alga. The evidence suggests that bluegreen algae synthesize ALA from glutamate in a manner similar to that observed in green plants and green algae.

delta-Aminolevulinic acid synthase from Euglena gracilis.

“…Although not yet completely characterized, this 5-carbon path to ALA has been shown to operate in greening tissues of higher plants (5)(6)(7) and in greening algae, including members of the Cyanophycae (8)(9)(10), Rhodophycae (11) and Chlorophycae (8,12,13), and Euglena (14).…”

Formation of the chlorophyll precursor delta-aminolevulinic acid in cyanobacteria requires aminoacylation of a tRNAGlu species

“…This ALA is then used in the synthesis of hemes, vitamin B12, and bacteriochlorophyll. In the chloroplasts of higher plants (2), archaebacteria (9,10), certain eubacteria (16,33,34), cyanobacteria (1,7,24,30), algae (19,20,50,51), and phytoflagellates (29,49), ALA is formed in the C-5 pathway from the five-carbon skeleton of glutamate. Eight molecules of glutamate-derived ALA provide all of the carbon and nitrogen atoms for the formation of the porphyrin nucleus of one molecule of chlorophyll.…”

Effects of Gabaculine on Pigment Biosynthesis in Normal and Nutrient Deficient Cells of Anacystis nidulans

“…We were surprised that GAB induced an excretion of ALA. Pigment synthesis in cyanobacteria is thought to be similar to that observed in higher plants. For example, Kipe-Nolt et al (17) demonstrated biosynthesis of ALA in cyanobacteria by monitoring ALA excretion in the presence of LA and suggested that glutamate is the major substrate for ALA synthesis (18). Isotope distribution studies using .…”

“…One of these, LA2, is a competitive inhibitor of ALA dehydratase (17,18), and effectively blocks protoporphyrin biosynthesis in both normal and iron-deficient cyanobacteria (1 1). The mechanism by which the second inhibitor, GAB, affects cyanobacteria is virtually unknown (12).…”