PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Biosynthetic Pathways”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed2001

Multiple biosynthetic pathways for vitamin B12: variations on a central theme.

The manner in which vitamin B12 is synthesized is detailed with emphasis on the different mechanisms for ring contraction encountered in aerobic and anaerobic organisms. The aerobic process utilizes two enzymes and is dependent on molecular oxygen, in stark contrast to the anaerobic mechanism which is controlled by cobalt and requires only one enzyme.

Aminolevulinic Acid↗
PubMed1984

Activity of prostaglandin biosynthetic pathways in rat pancreatic islets.

Isolated pancreatic islets of the rat were either prelabeled with [3H]arachidonic acid, or were incubated over the short term with the concomitant addition of radiolabeled arachidonic acid and a stimulatory concentration of glucose (17mM) for prostaglandin (PG) analysis. In prelabeled islets, radiolabel in 6-keto-PGF1 alpha, PGE2, and 15-keto-13,14-dihydro-PGF2 alpha increased in response to a 5 min glucose (17mM) challenge. In islets not prelabeled with arachidonic acid, label incorporation in 6-keto-PGF1 alpha increased, whereas label in PGE2 decreased during a 5 min glucose stimulation; after 30-45 min of glucose stimulation labeled PGE levels increased compared to control (2.8mM glucose) levels. Enhanced labelling of PGF2 alpha was not detected in glucose-stimulated islets prelabeled or not. Isotope dilution with endogenous arachidonic acid probably occurs early in the stimulus response in islets not prelabeled. D-Galactose (17mM) or 2-deoxyglucose (17mM) did not alter PG production. Indomethacin inhibited islet PG turnover and potentiated glucose-stimulated insulin release. Islets also converted the endoperoxide [3H]PGH2 to 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2, in a time-dependent manner and in proportions similar to arachidonic acid-derived PGs. In dispersed islet cells, the calcium ionophore ionomycin, but not glucose, enhanced the production of labeled PGs from arachidonic acid. Insulin release paralleled PG production in dispersed cells, however, indomethacin did not inhibit ionomycin-stimulated insulin release, suggesting that PG synthesis was not required for secretion. In confirmation of islet PGI2 turnover indicated by 6-keto-PGF1 alpha production, islet cell PGI2-like products inhibited platelet aggregation induced by ADP. These results suggest that biosynthesis of specific PGs early in the glucose secretion response may play a modulatory role in islet hormone secretion, and that different pools of cellular arachidonic acid may contribute to PG biosynthesis in the microenvironment of the islet.

Adenosine Diphosphate↗
PubMed2004

Recent advances in molecular biology and physiology of the prostaglandin E2-biosynthetic pathway.

Prostanoids represent a group of lipid mediators that are produced from arachidonic acid via the cyclooxygenase pathway. Once formed, the prostanoids are released from the cells and act on their cognate receptors on cell surfaces to exert their biological actions. Of these, prostaglandin E(2) (PGE(2)) is the most common prostanoid, being produced by a wide variety of cells and tissues and has a broad range of bioactivity. Recent advance in this field has led to identification and characterization of a number of enzymes that play roles in the biosynthesis of PGE(2), namely phospholipase A(2), cyclooxygenase and terminal PGE synthase. Each of these three reactions can be rate-limiting and involves multiple enzymes/isozymes that can act in different phases of cell activation and exhibit distinct functional coupling. In this review, we will overview a recent understanding of the molecular biology, regulatory mechanisms, and physiological functions of these enzymes.

Animals↗
PubMed2003

Genome-wide analysis of the L-methionine biosynthetic pathway in Corynebacterium glutamicum by targeted gene deletion and homologous complementation.

The genome sequence of Corynebacterium glutamicum, a gram-positive soil bacterium widely used as an amino acid producer, was analyzed by a similarity-based approach to elucidate the pathway for the biosynthesis of L-methionine. The functions of candidate ORFs were derived by gene deletion and, if necessary, by homologous complementation of suitable mutants. Of nine candidate ORFs (four of which were known previously), seven ORFs (cg0754 (metX), cg0755 (metY), cg1290 (metE), cg1702 (metH), cg2383 (metF), cg2536 (aecD), and cg2687 (metB)) were demonstrated to be part of the pathway while two others (cg0961 and cg3086) could be excluded. C. glutamicum synthesizes methionine in three, respectively four steps, starting from homoserine. C. glutamicum possesses two genes with similarity to homoserine acetyltransferases but only MetX can act as such while Cg0961 catalyzes a different, unknown reaction. For the incorporation of the sulfur moiety, the known functions of MetY and MetB could be confirmed and AecD was proven to be the only functional cystathionine beta-lyase in C. glutamicum, while Cg3086 can act neither as cystathionine gamma-synthase nor as cystathionine beta-lyase. Finally, MetE and MetH, which catalyze the conversion of L-homocysteine to L-methionine, could be newly identified, together with MetF which provides the necessary N(5)-methyltetrahydrofolate.

Amino Acid Sequence↗
PubMed1975

Studies on protoporphyrin biosynthetic pathway in Saccharomyces cerevisiae ; characterization of the tetrapyrrole intermediates.

An acellular extract of the yeast, Saccharomyces cerevisiae, incubated with ALA, is able to synthesize protoporphyrin from this precursor. Several tetrapyrrole intermediates were extracted from the medium and purified by silica gel chromatography. The chromatographic behaviour and the spectral properties of the isolated seven free carboxylic porphyrins (and of the corresponding esters), show that each product has a different carboxyle number, varying from eight (uroporphyrin) to two (protoporphyrin). The identification of five of them (octa- to tetracarboxymethyl-porphyrinester) is confirmed by mass spectrometry. The effect of physical factors (temperature, pH, time) on the protoporphyrin biosynthesis system indicates that the enzymes catalysing the first steps of the pathway (ALA leads to Coproporphyrin) are more stable than those catalysing the last steps (Coproporphyrin leads to Protoporphyrin). Results obtained with some enzymatic inhibitors (EDTA, OP, pCMB) show the sensitivity of the ALA dehydratase to OP and to pCMB (confirming therefore its nature as a metallo- and sulfhydryl enzyme) and also of the overall porphyrin synthesis system to these three agents.

Aminolevulinic Acid↗
PubMed2003

Substrate specificity and kinetics for VP14, a carotenoid cleavage dioxygenase in the ABA biosynthetic pathway.

The plant growth regulator, abscisic acid (ABA), is synthesized via the oxidative cleavage of an epoxy-carotenoid. Specifically, a double bond is cleaved by molecular oxygen and an aldehyde is formed at the site of cleavage in both products. The Vp14 gene from maize encodes an oxidative cleavage enzyme for ABA biosynthesis and the recombinant VP14 protein catalyzes the cleavage reaction in vitro. The enzyme has a strict requirement for a 9-cis double bond adjacent to the site of cleavage (the 11-12 bond), but shows some plasticity in other features of carotenoids that are cleaved. A kinetic analysis with the 9-cis isomer of five carotenoids displays several substrate activity relationships. One of the carotenoids was not readily cleaved, but inhibited the cleavage of another substrate in mixed assays. Of the remaining four carotenoids used in this study, three of the substrates have similar V(max) values. The V(max) for the cleavage of one carotenoid substrate was significantly higher. Molecular modeling and several three-dimensional quantitative substrate-activity relationship programs were used to analyze these results. In addition to a 9-cis double bond, the presence and orientation of the ring hydroxyl affects substrate binding or the subsequent cleavage. Additional variations that affect substrate cleavage are proposed.

Abscisic Acid↗
PubMed1999

The GPI biosynthetic pathway as a therapeutic target for African sleeping sickness.

African sleeping sickness is a debilitating and often fatal disease caused by tsetse fly transmitted African trypanosomes. These extracellular protozoan parasites survive in the human bloodstream by virtue of a dense cell surface coat made of variant surface glycoprotein. The parasites have a repertoire of several hundred immunologically distinct variant surface glycoproteins and they evade the host immune response by antigenic variation. All variant surface glycoproteins are anchored to the plasma membrane via glycosylphosphatidylinositol membrane anchors and compounds that inhibit the assembly or transfer of these anchors could have trypanocidal potential. This article compares glycosylphosphatidylinositol biosynthesis in African trypanosomes and mammalian cells and identifies several steps that could be targets for the development of parasite-specific therapeutic agents.

Aminoacyltransferases↗
PubMed2002

Biosynthetic pathway for production of a conjugated dienyl sex pheromone of a Plusiinae moth, Thysanoplusia intermixta.

Virgin females of Thysanoplusia intermixta (Lepidoptera; Noctuidae; Plusiinae) produce (5E,7Z)-5,7-dodecadienyl acetate as a main sex pheromone component. GC-MS analysis of the pheromone glands, which were treated with deuterated hexadecanoic, (Z)-11-hexadecenoic, and (Z)-7-dodecenoic acids, showed incorporation of the label into the dienyl component. Their incorporation rates confirmed that its biosynthesis proceeds in the following order: Delta11-desaturation of a C(16) acyl intermediate, chain shortening to a C(12) compound by beta-oxidation, Delta5-desaturation to produce a 5,7-dienyl system, reduction of the acyl group, and acetylation. These deuterated precursors also converted into a minor pheromone component, (Z)-7-docecenyl acetate, which might be prepared by the same pathway except for the step of Delta5-desaturation. While deuterium incorporation into the dienyl acetate was not observed in the extracts treated with other labeled dodecenoic acids with (E)-5-, (Z)-6-, and (E)-7-double bonds, the corresponding dodecenyl acetates were produced. This result showed low substrate specificity of the enzymes for reduction and acetylation. Labeled (Z)-10-hexadecenoic acid was not converted into a dodecenyl acetate, indicating the high substrate specificity of the enzyme for beta-oxidation.

Acetates↗
PubMed2002

10-Formyl-5,10-dideaza-acyclic-5,6,7,8-tetrahydrofolic acid (10-formyl-DDACTHF): a potent cytotoxic agent acting by selective inhibition of human GAR Tfase and the de novo purine biosynthetic pathway.

The synthesis of 10-formyl-DDACTHF (3) as a potential inhibitor of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide ribonucleotide transformylase (AICAR Tfase) is reported. Aldehyde 3, the corresponding gamma- and alpha-pentaglutamates 21 and 25 and related agents were evaluated for inhibition of folate-dependent enzymes including GAR Tfase and AICAR Tfase. The inhibitors were found to exhibit potent cytotoxic activity (CCRF-CEM IC(50) for 3=60nM) that exceeded their enzyme inhibition potency [K(i) (3)=6 and 1 microM for Escherichia coli GAR and human AICAR Tfase, respectively]. Cytotoxicity rescue by medium purines, but not pyrimidines, indicated that the potent cytotoxic activity is derived from selective purine biosynthesis inhibition and rescue by AICAR monophosphate established that the activity is derived preferentially from GAR versus AICAR Tfase inhibition. The potent cytotoxic compounds including aldehyde 3 lost activity against CCRF-CEM cell lines deficient in the reduced folate carrier (CCRF-CEM/MTX) or folylpolyglutamate synthase (CCRF-CEM/FPGS(-)) establishing that their potent activity requires both reduced folate carrier transport and polyglutamation. Unexpectedly, the pentaglutamates displayed surprisingly similar K(i)'s versus E. coli GAR Tfase and only modestly enhanced K(i)'s versus human AICAR Tfase. On the surface this initially suggested that the potent cytotoxic activity of 3 and related compounds might be due simply to preferential intracellular accumulation of the inhibitors derived from effective transport and polyglutamation (i.e., ca. 100-fold higher intracellular concentrations). However, a subsequent examination of the inhibitors against recombinant human GAR Tfase revealed they and the corresponding gamma-pentaglutamates were unexpectedly much more potent against the human versus E. coli enzyme (K(i) for 3, 14nM against rhGAR Tfase versus 6 microM against E. coli GAR Tfase) which also accounts for their exceptional cytotoxic potency.

Antineoplastic Agents↗
PubMed2003

Design, synthesis and biological evaluation of 10-CF3CO-DDACTHF analogues and derivatives as inhibitors of GAR Tfase and the de novo purine biosynthetic pathway.

The synthesis and evaluation of analogues and key derivatives of 10-CF3CO-DDACTHF as inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide transformylase (AICAR Tfase) are reported. Polyglutamate analogues of 1 were evaluated as inhibitors of Escherichia coli and recombinant human (rh) GAR Tfase, and AICAR Tfase. Although the pentaglutamate 6 was found to be the most active inhibitor of the series tested against rhGAR Tfase (Ki=0.004 microM), little distinction between the mono-pentaglutamate derivatives was observed (Ki=0.02-0.004 microM), suggesting that the principal role of the required polyglutamation of 1 is intracellular retention. In contrast, 1 and its defined polyglutamates 3-6 were much less inactive when tested against rhAICAR Tfase (Ki=65-0.120 microM) and very selective (> or =100-fold) for rh versus E. coli GAR Tfase. Additional key analogues of 1 were examined (7 and 8) and found to be much less active (1000-fold) highlighting the exceptional characteristics of 1.

Drug Design↗
PubMed1999

Crystal structure of Escherichia coli PurE, an unusual mutase in the purine biosynthetic pathway.

BACKGROUND: Conversion of 5-aminoimidazole ribonucleotide (AIR) to 4-carboxyaminoimidazole ribonucleotide (CAIR) in Escherichia coli requires two proteins - PurK and PurE. PurE has recently been shown to be a mutase that catalyzes the unusual rearrangement of N(5)-carboxyaminoimidazole ribonucleotide (N(5)-CAIR), the PurK reaction product, to CAIR. PurEs from higher eukaryotes are homologous to E. coli PurE, but use AIR and CO(2) as substrates to produce CAIR directly. RESULTS: The 1.50 A crystal structure of PurE reveals an octameric structure with 422 symmetry. A central three-layer (alphabetaalpha) sandwich domain and a kinked C-terminal helix form the folded structure of the monomeric unit. The structure reveals a cleft at the interface of two subunits and near the C-terminal helix of a third subunit. Co-crystallization experiments with CAIR confirm this to be the mononucleotide-binding site. The nucleotide is bound predominantly to one subunit, with conserved residues from a second subunit making up one wall of the cleft. CONCLUSIONS: The crystal structure of PurE reveals a unique quaternary structure that confirms the octameric nature of the enzyme. An analysis of the native crystal structure, in conjunction with sequence alignments and studies of co-crystals of PurE with CAIR, reveals the location of the active site. The environment of the active site and the analysis of conserved residues between the two classes of PurEs suggests a model for the differences in their substrate specificities and the relationship between their mechanisms.

Amino Acid Sequence↗
PubMed2002

Crystal structure of PMM/PGM: an enzyme in the biosynthetic pathway of P. aeruginosa virulence factors.

The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) from P. aeruginosa is required for the biosynthesis of two bacterial exopolysaccharides: alginate and lipopolysaccharide (LPS). Both of these molecules play a role in the virulence of P. aeruginosa, an important human pathogen known for its ability to develop antibiotic resistance and cause chronic lung infections in cystic fibrosis patients. The crystal structure of PMM/PGM shows that the enzyme has four domains, three of which have a similar three-dimensional fold. Residues from all four domains of the protein contribute to the formation of a large active site cleft in the center of the molecule. Detailed information on the active site of PMM/PGM lays the foundation for structure-based inhibitor design. Inhibitors of sufficient potency and specificity should impair the biosynthesis of alginate and LPS, and may facilitate clearance of the bacteria by the host immune system and increase the efficacy of conventional antibiotic treatment against chronic P. aeruginosa infections.

Animals↗