Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the biosynthetic conversion of glutamate to the tetrapyrrole precursor, delta-aminolevulinic acid (ALA), glutamate is activated at C-1 by glutamyl-tRNA synthetase-catalyzed ligation to tRNAGlu. Glutamyl-tRNA reductase next catalyzes reduction of the activated glutamate to glutamate-1-semialdehyde (GSA), which is then converted to ALA by GSA aminotransferase. Glutamyl-tRNA synthetase is known to require a divalent metal (usually Mg2+) for activity, but it has not been established whether Mg2+ or another metal ion is also required for glutamyl-tRNA reductase or GSA aminotransferase, because these enzymes have previously been assayed in combined incubations containing all factors required for conversion of glutamate to ALA. We now report the metal requirements individually for each of the three enzyme reactions. Glutamyl-tRNA reductase activity in extracts from both Chlorella vulgaris and Synechocystis sp. PCC 6803 was stimulated by Mg2+ and inhibited by EDTA. EDTA-pretreated Chlorella glutamyl-tRNA reductase-containing fraction had very little activity in the absence of added Mg2+, but recovered full activity in incubations containing added Mg2+. The divalent metal requirement could be met by Mg2+, Mn2+, or Ca2+. Maximum activity was reached at approximately 15 mM concentration of each of these metals, and higher concentrations were inhibitory. Zn2+ was inhibitory at micromolar concentrations. Chlorella glutamyl-tRNA synthetase showed a metal requirement that could be met by Mg2+ or Mn2+, but not Ca2+. Maximum activity was reached at approximately 15 mM Mg2+ or Mn2+. Although the presence of 10 mM Ca2+ did not affect the Mg2+ concentration optimum, Ca2+ increased the effectiveness of low concentrations of Mg2+. In contrast to glutamyl-tRNA synthetase and glutamyl-tRNA reductase, Chlorella GSA aminotransferase did not show a metal requirement or inhibition by EDTA. However, EDTA decreased nonenzymatic transformation of GSA to ALA.
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PMID:Metal requirements of the enzymes catalyzing conversion of glutamate to delta-aminolevulinic acid in extracts of Chlorella vulgaris and Synechocystis sp. PCC 6803. 791 10

In cyanobacteria, the biosynthesis of unsaturated fatty acids is initiated by delta 9 acyl-lipid desaturase which introduces the first double bond at the delta 9 position of a saturated fatty acid that has been esterified to a glycerolipid. We have cloned genes, designated desC, for delta 9 acyl-lipid desaturases from two cyanobacteria, namely Anabaena variabilis and Synechocystis sp. PCC 6803. These desaturases, when expressed in Escherichia coli, desaturated stearic acid to yield oleic acid at the C-1 positions of phosphatidylethanolamine and phosphatidylglycerol, but did not desaturate palmitic acid, palmitoleic acid, and cis-vaccenic acid. These results indicate that the delta 9 acyl-lipid desaturases are specific to stearic acid esterified at the C-1 position of a glycerolipid and are nonspecific with respect to the polar head group of the glycerolipid. The deduced amino acid sequences of the delta 9 acyl-lipid desaturases are similar in part to those of stearoyl-CoA desaturases of the rat, the mouse, and Saccharomyces cerevisiae, but not to those of acyl-(acyl-carrier-protein) desaturases of higher plants.
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PMID:delta 9 Acyl-lipid desaturases of cyanobacteria. Molecular cloning and substrate specificities in terms of fatty acids, sn-positions, and polar head groups. 792 59

The side chain of residue threonine 65 within the active site of ribulosebisphosphate carboxylase participates in a network of hydrogen bonds and ionic interactions involving the phosphate moiety attached to C-1 of the substrate. This residue was replaced with serine, alanine, and valine in the enzyme from Synechococcus PCC 6301. The mutant enzymes were stable, expressed abundantly by Escherichia coli, and retained the ability to form gel-filterable complexes with the reaction-intermediate analog, 2'-carboxyarabinitol-1,5-bisphosphate. The substitutions reduced the kcat/Km(CO2) (where kcat is the substrate-saturated turnover rate) of the enzyme from 17- to 340-fold with the more radical substitutions causing more severe reductions. The CO2/O2 specificity also deteriorated progressively, the valine replacement causing a 2.3-fold reduction. In concert with these changes, a compound tentatively identified as 1-deoxy-D-glycero-2,3-pentodiulose-5-phosphate, the product of beta elimination of the 2,3-enediol(ate) intermediate of the catalytic reaction, appeared among the reaction products in progressively increasing amounts. In the case of the valine substitution, it comprised 13% of the ribulose bisphosphate consumed. The mutant enzymes also partitioned more of their reaction flux to pentulose bisphosphate isomers of ribulose bisphosphate. By contrast, the diversion of carboxylated product to pyruvate, as a result of beta elimination of the three-carbon aci-carbanion intermediate of the carboxylation reaction, was ameliorated by the replacements, the valine mutant showing a 5-fold improvement in this parameter. These observations focus attention on a geometric conflict which exists between the requirements for stabilization of the 5-carbon enediol(ate) and 3-carbon aci-carbanion intermediates. This conflict must be resolved by a change in the angle of the C-1/bridge oxygen bond during each catalytic cycle. The network of hydrogen bonds involving the side chain of threonine 65 must play a crucial role in facilitating reaction of the enediol(ate) with the gaseous substrate and in shepherding this subsequent movement.
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PMID:Mutations of an active site threonyl residue promote beta elimination and other side reactions of the enediol intermediate of the ribulosebisphosphate carboxylase reaction. 813 34