The jasmonate biochemical pathway.

Plants possess an interrelated and interacting family of potent fatty acid-derived regulators--the jasmonates. These compounds, which play roles in both defense and development, are derived from tri-unsaturated fatty acids [alpha-linolenic acid (18:3) or 7Z,10Z,13Z-hexadecatrienoic acid (16:3)]. The lipoxygenase-catalyzed addition of molecular oxygen to alpha-linolenic acid initiates jasmonate synthesis by providing a 13-hydroperoxide substrate for the formation of an unstable allene oxide that is then subject to enzyme-guided cyclization to produce 12-oxo-phytodienoic acid (OPDA). OPDA, a key regulatory lipid in the plant immune system, has several fates, including esterification into plastid lipids or transformation into the 12-carbon co-regulator jasmonic acid (JA). JA, the best-characterized member of the family, regulates both male and female fertility (depending on the plant species), and is an important mediator of defense gene expresssion. JA is itself a substrate for further diverse modifications. Genetic dissection of the pathway is revealing how the different jasmonates modulate different physiological processes. Each new family member that is discovered provides another key to understanding the fine control of gene expression in immune responses, in the initiation and maintenance of long-distance signal transfer in response to wounding, and in the regulation of fertility, among other processes. The Jasmonate Biochemical Pathway provides an overview of the growing jasmonate family, and new members will be included in future versions of the Connections Map. Science Viewpoint R. Liechti, E. E. Farmer, The jasmonate pathway. Science 296, 1649-1650 (2002). [Abstract] [Full Text]

Chemical Reactions Involving Aggregates, HR-15, 1960

The discussion presented below concerns the section on "Unidentified Cement-Aggregate Reactions" in which mention is made of concrete deterioration related to argillaceous dolomitic limestone aggregates. A considerable amount of research has been conducted on carbonate aggregate-cement reactions as part of the general study on the suitability of carbonate rocks as concrete aggregate which inadvertently did not reach the authors in time to be incorporated in their paper. These reactions which occur in response to the alkaline environment of concrete are not typical alkali-aggregate reactions associated with siliceous aggregates such as opaline cherts, volcanic glasses and etc. The reactions are associated with certain carbonate aggregates whose service records indicate deleterious performance in concrete has occurred. It is my purpose to review briefly carbonate aggregate research conducted at Iowa State University and present some new data on the problem of carbonate aggregate-cement paste reactions.

Convenient synthesis of C75, an inhibitor of FAS and CPT1

C75 is a synthetic racemic α-methylene-γ-butyrolactone exhibiting anti-tumoral properties in vitro and in vivo as well as inducing hypophagia and weight loss in rodents. These interesting properties are thought to be a consequence of the inhibition of the key enzymes FAS and CPT1 involved in lipid metabolism. The need for larger amounts of this compound for biological evaluation prompted us to develop a convenient and reliable route to multigram quantities of C75 from easily available ethyl penta-3,4-dienoate 6. A recently described protocol for the addition of 6 to a mixture of dicyclohexylborane and nonanal followed by acidic treatment of the crude afforded lactone 8, as a mixture of cis and trans isomers, in good yield. The DBU-catalyzed isomerization of the methyl esters 9 arising from 8 gave a 10:1 trans/cis mixture from which the trans isomer was isolated and easily transformed into C75. The temporary transformation of C75 into a phenylseleno ether derivative makes its purification, manipulation and storage easier.

Enzyme activities and pectin breakdown of sapodilla submitted to 1-methylcyclopropene

The objective of this work was to investigate the influence of 1-methylcyclopropene (1-MCP) at 300 nL L-1 on activities of cell wall hidrolytic enzymes and pectin breakdown changes which Sapodilla (Manilkara zapota cv. Itapirema 31) cell wall undergoes during ripening. Sapodilla were treated with ethylene antagonist 1-MCP at 300 nL L-1 for 12 hours and then, stored under a modified atmosphere at 25º C for 23 days. Firmness, total and soluble pectin and cell wall enzymes were monitored during storage. 1-MCP at 300 nL L-1 for 12 hours delayed significantly softening of sapodilla for 11 days at 25º C. 1-MCP postharvest treatment affected the activities of cell wall degrading enzymes pectinmethylesterase and polygalacturonase and completely suppressed increases in beta-galactosidase for 8 days, resulting in less pectin solubilization. Beta-galactosidase seems relevant to softening of sapodilla and is probably responsible for modification of both pectin and xyloglucan-cellulose microfibril network.

The deubiquitinating enzyme AMSH3 is required for intracellular trafficking and vacuole biogenesis in Arabidopsis thaliana.

Ubiquitination, deubiquitination, and the formation of specific ubiquitin chain topologies have been implicated in various cellular processes. Little is known, however, about the role of ubiquitin in the development of cellular organelles. Here, we identify and characterize the deubiquitinating enzyme AMSH3 from Arabidopsis thaliana. AMSH3 hydrolyzes K48- and K63-linked ubiquitin chains in vitro and accumulates both ubiquitin chain types in vivo. amsh3 mutants fail to form a central lytic vacuole, accumulate autophagosomes, and mis-sort vacuolar protein cargo to the intercellular space. Furthermore, AMSH3 is required for efficient endocytosis of the styryl dye FM4-64 and the auxin efflux facilitator PIN2. We thus present evidence for a role of deubiquitination in intracellular trafficking and vacuole biogenesis.

Hypertension. Angio-oedème sous inhibition de l'enzyme de conversion de l'angiotensine et de la dipeptidyl-peptidase-4 [Angioedema during ACE and DPP-4 inhibition]

Angioedema is a rare side effect of angiotensin converting enzyme (ACE) inhibitors. Its cause is probably related to the accumulation of bradykinin and substance P, i.e. two proinflammatory peptides normally inactivated by ACE. Angioedema occurs most of the time at the early phase of treatment, but may also develop during long-term treatment. It might involve the gastro-intestinal tract, leading to abdominal pain, vomiting and/or diarrhea, as well as pancreatitis. Dipeptidyl-ptidase-4 (DPP-4) is another enzyme allowing the degradation of bradykinin and substance P. Co-administering an ACE inhibitor and a DPP-4 inhibitor (as an antidiabetic agent) increases significantly the risk of angioedema.

Mutations in B3GALT6, which encodes a glycosaminoglycan linker region enzyme, cause a spectrum of skeletal and connective tissue disorders.

Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.

Lack of angiotensin I accumulation after converting enzyme blockade by enalapril or lisinopril in man.

In nine normal volunteers, a series of five venous blood samples was obtained before and up to 24 h after converting enzyme inhibition by a single oral dose of enalapril or lisinopril. Plasma renin activity and blood angiotensin I were measured. A close linear relationship was found between the increase in plasma renin activity and the increase in blood angiotensin I. The linear correlation between plasma renin activity and blood angiotensin I remained after converting enzyme inhibition. Thus, the rise in angiotensin I after inhibition of the conversion of angiotensin I to angiotensin II is due to an enhanced release of renin rather than to accumulation of angiotensin I.

Stereoselective Acetate Aldol Reactions From Metal Enolates

This review deals with metal enolate-mediated stereoselective acetate aldol reactions. It summarizes recent advances on aldol additions of unsubstituted metal enolates from chiral auxiliaries, stoichiometric and catalytic Lewis acids, or acting in substrate- controlled reactions, which provide stereocontrolled aldol transformations that allow the efficient synthesis of structurally complex natural products.

Nucleophile-Catalyzed Additions to Activated Triple Bonds. Protection of Lactams, Imides, and Nucleosides with MocVinyl and Related Groups

Additions of lactams, imides, (S)-4-benzyl-1,3-oxazolidin-2-one, 2-pyridone, pyrimidine-2,4-diones (AZT derivatives), or inosines to the electron-deficient triple bonds of methyl propynoate, tert-butyl propynoate, 3-butyn-2-one, N-propynoylmorpholine, or N-methoxy-N-methylpropynamide in the presence of many potential catalysts were examined. DABCO and, second, DMAP appeared to be the best (highest reaction rates and E/Z ratios), while RuCl3, RuClCp*(PPh3)2, AuCl, AuCl(PPh3), CuI, and Cu2(OTf)2 were incapable of catalyzing such additions. The groups incorporated (for example, the 2-(methoxycarbonyl)ethenyl group that we name MocVinyl) serve as protecting groups for the above-mentioned heterocyclic CONH or CONHCO moieties. Deprotections were accomplished via exchange with good nucleophiles: the 1-dodecanethiolate anion turned out to be the most general and efficient reagent, but in some particular cases other nucleophiles also worked (e.g., MocVinyl-inosines can be cleaved with succinimide anion). Some structural and mechanistic details have been accounted for with the help of DFT and MP2 calculations.

Convenient synthesis of C75, an inhibitor of FAS and CPT1

C75 is a synthetic racemic α-methylene-γ-butyrolactone exhibiting anti-tumoral properties in vitro and in vivo as well as inducing hypophagia and weight loss in rodents. These interesting properties are thought to be a consequence of the inhibition of the key enzymes FAS and CPT1 involved in lipid metabolism. The need for larger amounts of this compound for biological evaluation prompted us to develop a convenient and reliable route to multigram quantities of C75 from easily available ethyl penta-3,4-dienoate 6. A recently described protocol for the addition of 6 to a mixture of dicyclohexylborane and nonanal followed by acidic treatment of the crude afforded lactone 8, as a mixture of cis and trans isomers, in good yield. The DBU-catalyzed isomerization of the methyl esters 9 arising from 8 gave a 10:1 trans/cis mixture from which the trans isomer was isolated and easily transformed into C75. The temporary transformation of C75 into a phenylseleno ether derivative makes its purification, manipulation and storage easier.

Orthogonal protection of peptides and peptoids for cyclization by the thiol-ene reaction and conjugation

Cyclic peptides and peptoids were prepared using the thiolene Michael-type reaction. The linear precursors were provided with additional functional groups allowing for subsequent conjugation: an orthogonally protected thiol, a protected maleimide, or an alkyne. The functional group for conjugation was placed either within the cycle or in an external position. The click reactions employed for conjugation with suitably derivatized nucleoside or oligonucleotides were either cycloadditions (Diels-Alder, Cu(I)-catalyzed azide-alkyne) or the same Michael-type reaction as for cyclization.

Transcriptional regulatory patterns of the myelin basic protein and malic enzyme genes by the thyroid hormone receptors alpha1 and beta1.

While there is evidence that the two ubiquitously expressed thyroid hormone (T3) receptors, TRalpha1 and TRbeta1, have distinct functional specificities, the mechanism by which they discriminate potential target genes remains largely unexplained. In this study, we demonstrate that the thyroid hormone response elements (TRE) from the malic enzyme and myelin basic protein genes (METRE and MBPTRE) respectively, are not functionally equivalent. The METRE, which is a direct repeat motif with a 4-base pair gap between the two half-site hexamers binds thyroid hormone receptor as a heterodimer with 9-cis-retinoic acid receptor (RXR) and mediates a high T3-dependent activation in response to TRalpha1 or TRbeta1 in NIH3T3 cells. In contrast, the MBPTRE, which consists of an inverted palindrome formed by two hexamers spaced by 6 base pairs, confers an efficient transactivation by TRbeta1 but a poor transactivation by TRalpha1. While both receptors form heterodimers with RXR on MBPTRE, the poor transactivation by TRalpha1 correlates also with its ability to bind efficiently as a monomer. This monomer, which is only observed with TRalpha1 bound to MBPTRE, interacts neither with N-CoR nor with SRC-1, explaining its functional inefficacy. However, in Xenopus oocytes, in which RXR proteins are not detectable, the transactivation mediated by TRalpha1 and TRbeta1 is equivalent and independent of a RXR supply, raising the question of the identity of the thyroid hormone receptor partner in these cells. Thus, in mammalian cells, the binding characteristics of TRalpha1 to MBPTRE (i.e. high monomer binding efficiency and low transactivation activity) might explain the particular pattern of T3 responsiveness of MBP gene expression during central nervous system development.