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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We isolated the gene for citrate synthase (citrate oxaloacetate lyase; EC 4.1.3.7) from Saccharomyces cerevisiae and ablated it by inserting the yeast LEU2 gene within its reading frame. This revealed a second, nonmitochondrial citrate synthase. Like the mitochondrial enzyme, this enzyme was sensitive to glucose repression. It did not react with antibodies against mitochondrial citrate synthase. Haploid cells lacking a gene for mitochondrial citrate synthase grew somewhat slower than wild-type yeast cells, but exhibited no auxotrophic growth requirements.
Mol Cell Biol 1986 Feb
PMID:Extramitochondrial citrate synthase activity in bakers' yeast. 302 50

The tricarboxylic acid cycle occurs within the mitochondria of the yeast Saccharomyces cerevisiae. A nuclear gene encoding the tricarboxylic acid cycle enzyme citrate synthase has previously been isolated (M. Suissa, K. Suda, and G. Schatz, EMBO J. 3:1773-1781, 1984) and is referred to here as CIT1. We report here the isolation, by an immunological method, of a second nuclear gene encoding citrate synthase (CIT2). Disruption of both genes in the yeast genome was necessary to produce classical citrate synthase-deficient phenotypes: glutamate auxotrophy and poor growth on rich medium containing lactate, a nonfermentable carbon source. Therefore, the citrate synthase produced from either gene was sufficient for these metabolic roles. Transcription of both genes was maximally repressed in medium containing both glucose and glutamate. However, transcription of CIT1 but not of CIT2 was derepressed in medium containing a nonfermentable carbon source. The significance of the presence of two genes encoding citrate synthase in S. cerevisiae is discussed.
Mol Cell Biol 1986 Jun
PMID:Saccharomyces cerevisiae contains two functional citrate synthase genes. 302 12

Coenzyme Q10 (CoQ10) was studied in papillary muscle from 18 patients (52-67 years, 2 females) subjected to open heart surgery due to mitral valve disease. In addition the enzyme activities of lactate dehydrogenase (LD) with its five isozymes, citrate synthase (CS) and mitochondrial CK (CK-MIT) were determined. Myocardial function was assessed by means of left ventricle (LV) angiography. CoQ10 averaged 0.39 (range 0.26-0.59) micrograms x mg-1 dw. On an individual basis CoQ10 was related to CS activity although not as closely as CK-MIT (r = 0.45, p less than 0.05 versus r = 0.86, p less than 0.001). The ratio (CoQ10) x (CS activity)-1 was calculated to represent mitochondrial quality. The level of LD3 fraction increase was used to mark for the degree of metabolic stress in the heart. LD3 fraction was negatively related to the quality index (r = -0.71, p less than 0.001). Thus, those with a low CoQ10 per unit of CS activity had also a high LD3 isozyme fraction. In a subset of 12 patients with isolated mitral regurgitation due to myxomatous valve degeneration, CoQ10 and the ratio CoQ10 over CS decreased with the degree of LV function impairment (r = -0.58, p less than 0.05 and r = -0.68, p less than 0.05, respectively). The quality index takes into account not only enzyme activity but also the potential for control of free oxygen radicals.
Mol Cell Biochem 1988 Nov
PMID:Coenzyme Q10 and key enzyme activities in papillary muscle related to left ventricle function in mitral valve disease. 323 Dec 16

Axenic culture amastigote-like forms of Trypanosoma cruzi, grown at 28 degrees C, reach a stationary phase after two generations, and differentiate to epimastigotes, which then resume growth. Axenic culture amastigotes readily ferment glucose to succinate and acetate, and do not excrete NH3; they have high activities of hexokinase and phosphoenolpyruvate carboxykinase, and very low citrate synthase activity; cytochrome o is absent, and cytochrome b-like is present at a very low level. Epimastigotes catabolize glucose and produce succinate and acetate at a considerably lower rate; they exhibit lower levels of hexokinase and carboxykinase, and much higher levels of citrate synthase and cytochromes o and b-like. They catabolize amino acids, as shown by excretion of NH3 to the medium. The results suggest that axenic culture amastigotes have an essentially glycolytic metabolism, and they acquire the ability to oxidize substrates such as amino acids only after differentiation to epimastigotes.
Mol Biochem Parasitol 1987 Nov
PMID:Aerobic glucose fermentation by Trypanosoma cruzi axenic culture amastigote-like forms during growth and differentiation to epimastigotes. 332 2

Saccharomyces cerevisiae contains two genes, CIT1 and CIT2, encoding functional citrate synthase (K.-S. Kim, M. S. Rosenkrantz, and L. Guarente, Mol. Cell. Biol. 6:1936-1942, 1986). We show here that CIT2 encodes a nonmitochondrial form of citrate synthase. The DNA sequence of CIT2 presented provides a possible explanation for why the CIT2 product, unlike the CIT1 product, fails to be imported into mitochondria. While the products of these two genes are highly homologous, they diverge strikingly at their amino termini. The amino terminus of the CIT1 primary translation product extends 39 residues beyond the amino termini of Escherichia coli and porcine citrate synthases. This extension consists of a typical mitochondrial targeting motif. The amino terminus of the CIT2 primary translation product extends 20 residues beyond the amino termini of the E. coli and porcine enzymes. The CIT2-encoded extension is not homologous to that of CIT1, resulting in a nonmitochondrial localization of the product. The CIT2-encoded extension, however, does bear certain similarities to mitochondrial targeting sequences. The possible role of this sequence in targeting this CIT2 product to a nonmitochondrial organelle is discussed.
Mol Cell Biol 1986 Dec
PMID:Mitochondrial and nonmitochondrial citrate synthases in Saccharomyces cerevisiae are encoded by distinct homologous genes. 354 Jun 14

The chemical nature of the inactivation of citrate synthase by S-(4-bromo-2,3-dioxobutyl)-CoA, an active site-directed irreversible inhibitor, has been investigated. Active site-directed inactivation leads to derivatization of either Lys22 by epsilon-amino Schiff base formation or Glu363 by apparent alkylation of the gamma-carboxyl group, respectively. Lys22 is labeled in the tight (catalytic) form of the enzyme while Glu363 is labeled in the open (product release) form. Glu363 and Lys22 are both located at or near the entrance to an active site in the crystal structure of citrate synthase (Remington, S., Wiegand, G., and Huber, R. (1982) J. Mol. Biol. 158, 111-152). Glu363 is in the sequence of the protomer forming the active site while Lys22 is in the sequence of the other polypeptide in the homodimer. Labeling in this region appears to inactivate the enzyme by preventing access of substrates to the active site. A distinct and separate labeling process involves derivatization of Asn192 in the tight (catalytic) form and Ser198 and/or Ser199 in the open (product release) form at a locus far removed from the active site. Labeling at the second site may simply identify chemically reactive residues, or it may identify the binding site for long chain acyl-CoA, which has been identified as a possible allosteric negative effector of citrate synthase (Caggiano, A. V., and Powell, G. L. (1979) J. Biol. Chem. 254, 2800-2806). This second labeling process apparently inactivates the enzyme by interfering with catalytically essential conformational changes.
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PMID:S-(4-bromo-2,3-dioxobutyl)-CoA labels two distinct sites on citrate synthase. 372 59

The review deals with the phenomenology in the studies on characteristics of surface antigenic and immunogenic structures of Rickettsia, their cellular membranes, the processes of metabolic cooperation and interaction with the host cells, and the structure of Rickettsia genome. The data on active antigenic and immunogenic proteins distribution in inner and outer membranes and on osmotically active functioning cellular membrane, including the specific substrate carriers, are discussed. The materials, are presented on the specific ADP-ATP transport system, slightly different from the mitochondrial one, in evidence that Rickettsia utilize ATP in two pathways: endogenous and exogenous. The metabolic regulatory processes, controlled by adenine nucleotides are discussed that could be used as a means of fitting to constantly changing conditions of Rickettsia ecological niche. The Rickettsia deficiency in AMP catabolism enzyme could be used for allosteric-regulation of citrate synthase, the key enzyme in the Krebs cycle. The data on the mol mass of Rickettsia DNA (1 x 10(9)) and the characteristics of plasmids are presented. In conclusion new data on molecular cloning of Rickettsia genes in vector plasmids and the restriction analysis of specific DNA sequences are discussed.
Mol Gen Mikrobiol Virusol 1985 Apr
PMID:[Biochemical and genetical study of Rickettsia]. 391 24

Cells of the aerotolerant anaerobe Giardia lamblia respire in the presence of oxygen. Endogenous respiration is stimulated by glucose but not by other carbohydrates and Krebs cycle intermediates. Endogenous and glucose-stimulated respiration are insensitive to cyanide, malonate, and 2,4-dinitrophenol, but are inhibited by atabrin and iodoacetamide. G. lamblia produces ethanol, acetate and CO2 both aerobically and anaerobically either from endogenous reserves or exogenous glucose. Molecular hydrogen is not produced. The following enzyme activities were detected in homogenates: hexokinase, fructose-biphosphate aldolase, pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate dehydrogenase (decarboxylating), pyruvate synthase, acetyl-CoA synthetase, alcohol dehydrogenase (NADP+), NADH dehydrogenase, NADPH dehydrogenase, NADPH oxidoreductase and superoxide dismutase. The enzymes of energy and carbohydrate metabolism are nonsedimentable (109 000 x g for 30 min). Activities of lactate dehydrogenase, hydrogenase, phosphate acetyltransferase, acetate kinase, citrate synthase, succinate dehydrogenase, fumarate hydratase and catalase were below the limits of detection. The results suggest the occurrence of glycolysis, energy production by substrate level phosphorylation and a flavin, iron-sulfur protein mediated electron transport system as well as the absence of cytochrome mediated oxidative phosphorylation and functional Krebs cycle.
Mol Biochem Parasitol 1980 Mar
PMID:Energy metabolism of the anaerobic protozoon Giardia lamblia. 610 7

Pulse-chase labeling in whole cells and cell-free protein synthesis were used to establish that the mitochondrial enzyme citrate synthase is made as a larger precursor in Saccharomyces cerevisiae. A 54,000 Mr precursor form appeared to be a primary translation product since it could be labeled with N-[35S]formylmethionine in vitro. The induction of citrate synthase was monitored in S. cerevisiae cells grown on fermentable (glucose) and nonfermentable (ethanol and glycerol) carbon sources. The amount of citrate synthase activity and immune-reactive protein increased more than 15-fold as S. cerevisiae cells entered the stationary growth phase on glucose-containing medium. This increase was paralleled by an increase in translatable RNA for the enzyme. When cells were grown on a nonfermentable carbon source, no increase in either citrate synthase or its mRNA was detected. The results suggest that the release of citrate synthase from catabolite repression may occur at the level of transcription.
Mol Cell Biol 1984 Feb
PMID:Derepression of citrate synthase in Saccharomyces cerevisiae may occur at the level of transcription. 619 62

Concentric left ventricular hypertrophy was produced in puppies by coarctation banding of the aorta at age 7 weeks. Hemodynamic, morphologic and biochemical studies were carried out 18 months after the operation. Systolic blood pressure proximal to the aortic constriction was 216 +/- 16 mmHg in experimental dogs compared with 115 +/- 5 mmHg in littermate control dogs. Ejection fraction of control and experimental dogs were 59 +/- 4 and 64 +/- 7, respectively. The left ventricular end-diastolic pressure was 6.0 +/- 0.4 in control and 8.4 +/- 1.1 in experimental dogs. There was no sign of overt heart failure in the experimental dogs. Anatomical analysis of different regions of the heart indicated that LV mass in the experimental dogs was increased by about 60%. Ultrastructure of mitochondria in situ, as observed under electron microscope, was normal both in control and hypertrophic hearts. Mitochondria isolated from epicardial and endocardial regions of the stable hypertrophic hearts showed normal rates of respiration, phosphorylation, citrate synthase, and cytochrome c oxidase activities compared to those isolated from hearts of littermate control dogs. It was, therefore, concluded that mitochondrial function is adequately preserved to meet the increased demand for energy in this model of stable cardiac hypertrophy of long duration.
J Mol Cell Cardiol 1983 Apr
PMID:Mitochondrial function in canine experimental cardiac hypertrophy. 630 71


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