scholarly journals A Positive Role for Rhizobitoxine in Rhizobium-legume Symbiosis

1999 ◽  
Vol 12 (12) ◽  
pp. 1082-1089 ◽  
Author(s):  
Samuel Duodu ◽  
T. V. Bhuvaneswari ◽  
Thomas J. W. Stokkermans ◽  
N. Kent Peters
Keyword(s):  
Ethylene Biosynthesis ◽  
Nodule Development ◽  
Ethylene Inhibitors ◽  
Wild Type ◽  
Positive Role ◽  
Rate Limiting Step ◽  
Mutant Strains ◽  
Legume Symbiosis ◽  
Exogenous Ethylene ◽  
Rate Limiting

Although Bradyrhizobium elkanii is a mutualistic symbiont of legumes, it synthesizes a phytotoxin, rhizobitoxine, that causes chlorosis on a variety of legume hosts, giving a pathogenic character to these interactions. No positive role for rhizobitoxine has been previously demonstrated. Interestingly, rhizobitoxine inhibits the rate-limiting step for ethylene biosynthesis, a plant hormone known to inhibit or down-regulate nodule development. We hypothesized that rhizobitoxine plays a positive role in nodule development through its inhibition of ethylene biosynthesis. To test this hypothesis, host plants of B. elkanii were screened for a differential nodulation response to the wild-type and rhizobitoxine mutant strains. In Vigna radiata (mungbean), the rhizobitoxine mutant strains induced many aborted nodules arrested at all stages of pre-emergent and post-emergent development and formed significantly fewer mature nodules than the wild type. Experiments revealed that nodulation of mungbean plants is sensitive to exogenous ethylene, and that the ethylene inhibitors aminoethoxyvinylglycine and Co2+ were able to partially restore a wild-type nodulation pattern to the rhizobitoxine mutants. This is the first demonstration of a nodulation phenotype of the rhizobitoxine mutants and suggests that rhizobitoxine plays a positive and necessary role in Rhizobium-legume symbiosis through its inhibition of ethylene biosynthesis.

The hydrolysis and biogas production of complex cellulosic substrates using three anaerobic biomass sources

2013 ◽  
Vol 67 (2) ◽  
pp. 293-298 ◽  
Author(s):  
C. Keating ◽  
D. Cysneiros ◽  
T. Mahony ◽  
V. O'Flaherty
Keyword(s):  
Biogas Production ◽  
Positive Role ◽  
Diverse Range ◽  
Factors Affecting ◽  
Rate Limiting Step ◽  
Solid Substrates ◽  
Different Temperatures ◽  
Anaerobic Biomass ◽  
Rate Limiting ◽  
Hydrolysis Of

In this study, the ability of various sludges to digest a diverse range of cellulose and cellulose-derived substrates was assessed at different temperatures to elucidate the factors affecting hydrolysis. For this purpose, the biogas production was monitored and the specific biogas activity (SBA) of the sludges was employed to compare the performance of three anaerobic sludges on the degradation of a variety of complex cellulose sources, across a range of temperatures. The sludge with the highest performance on complex substrates was derived from a full-scale bioreactor treating sewage at 37 °C. Hydrolysis was the rate-limiting step during the degradation of complex substrates. No activity was recorded for the synthetic cellulose compound carboxymethylcellulose (CMC) using any of the sludges tested. Increased temperature led to an increase in hydrolysis rates and thus SBA values. The non-granular nature of the mesophilic sludge played a positive role in the hydrolysis of solid substrates, while the granular sludges proved more effective on the degradation of soluble compounds.

ACC-OXIDASE IS THE RATE LIMITING STEP IN ETHYLENE BIOSYNTHESIS DURING POSTHARVEST STORAGE OF TOMATO

2012 ◽  
pp. 429-434 ◽  
Author(s):  
B. Van de Poel ◽  
I. Bulens ◽  
M.L.A.T.M. Hertog ◽  
B.M. Nicolaï ◽  
A.H. Geeraerd ◽  
...  
Keyword(s):  
Acc Oxidase ◽  
Ethylene Biosynthesis ◽  
Postharvest Storage ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Three factors that modulate the activity of class D β-lactamases and interfere with the post-translational carboxylation of Lys70

2010 ◽  
Vol 432 (3) ◽  
pp. 495-506 ◽  
Author(s):  
Lionel Vercheval ◽  
Cédric Bauvois ◽  
Alexandre di Paolo ◽  
Franck Borel ◽  
Jean-Luc Ferrer ◽  
...  
Keyword(s):  
Active Site ◽  
Chloride Ions ◽  
Side Chain ◽  
Wild Type ◽  
Post Translational Modification ◽  
Rate Limiting Step ◽  
Class D ◽  
The Individual ◽  
Rate Limiting

The activity of class D β-lactamases is dependent on Lys70 carboxylation in the active site. Structural, kinetic and affinity studies show that this post-translational modification can be affected by the presence of a poor substrate such as moxalactam but also by the V117T substitution. Val117 is a strictly conserved hydrophobic residue located in the active site. In addition, inhibition of class D β-lactamases by chloride ions is due to a competition between the side chain carboxylate of the modified Lys70 and chloride ions. Determination of the individual kinetic constants shows that the deacylation of the acyl–enzyme is the rate-limiting step for the wild-type OXA-10 β-lactamase.

scholarly journals Mutations in VPS16 and MRT1Stabilize mRNAs by Activating an Inhibitor of the Decapping Enzyme

1999 ◽  
Vol 19 (11) ◽  
pp. 7568-7576 ◽  
Author(s):  
Shuang Zhang ◽  
Carol J. Williams ◽  
Kevin Hagan ◽  
Stuart W. Peltz
Keyword(s):  
Rna Stability ◽  
Wild Type ◽  
Mrna Decapping ◽  
Hsp70 Family ◽  
Rate Limiting Step ◽  
Nonsense Codon ◽  
Decapping Enzyme ◽  
Rate Limiting

ABSTRACT Decapping is a rate-limiting step in the decay of many yeast mRNAs; the activity of the decapping enzyme therefore plays a significant role in determining RNA stability. Using an in vitro decapping assay, we have identified a factor, Vps16p, that regulates the activity of the yeast decapping enzyme, Dcp1p. Mutations in the VPS16 gene result in a reduction of decapping activity in vitro and in the stabilization of both wild-type and nonsense-codon-containing mRNAs in vivo. The mrt1-3 allele, previously shown to affect the turnover of wild-type mRNAs, results in a similar in vitro phenotype. Extracts from both vps16 and mrt1 mutant strains inhibit the activity of purified Flag-Dcp1p. We have identified a 70-kDa protein which copurifies with Flag-Dcp1p as the abundant Hsp70 family member Ssa1p/2p. Intriguingly, the interaction with Ssa1p/2p is enhanced in strains with mutations in vps16 ormrt1. We propose that Hsp70s may be involved in the regulation of mRNA decapping.

scholarly journals A rare tRNA-Arg(CCU) that regulates Ty1 element ribosomal frameshifting is essential for Ty1 retrotransposition in Saccharomyces cerevisiae.

Genetics ◽  
1993 ◽  
Vol 135 (2) ◽  
pp. 309-320 ◽  
Author(s):  
K Kawakami ◽  
S Pande ◽  
B Faiola ◽  
D P Moore ◽  
J D Boeke ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Processing ◽  
Ribonuclease H ◽  
Wild Type ◽  
Ribosomal Frameshifting ◽  
Translational Frameshifting ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Ty1 Retrotransposition ◽  
Rate Limiting

Abstract Translation of the yeast retrotransposon Ty1 TYA1(gag)-TYB1(pol) gene occurs by a +1 ribosomal frameshifting event at the sequence CUU AGG C. Because overexpression of a low abundance tRNA-Arg(CCU) encoded by the HSX1 gene resulted in a reduction in Ty1 frameshifting, it was suggested that a translational pause at the AGG-Arg codon is required for optimum frameshifting. The present work shows that the absence of tRNA-Arg(CCU) affects Ty1 transposition, translational frameshifting, and accumulation of mature TYB1 proteins. Transposition of genetically tagged Ty1 elements decreases at least 50-fold and translational frameshifting increases 3-17-fold in cells lacking tRNA-Arg(CCU). Accumulation of Ty1-integrase and Ty1-reverse transcriptase/ribonuclease H is defective in an hsx1 mutant. The defect in Ty1 transposition is complemented by the wild-type HSX1 gene or a mutant tRNA-Arg(UCU) gene containing a C for T substitution in the first position of the anticodon. Overexpression of TYA1 stimulates Ty1 transposition 50-fold above wild-type levels when the level of transposition is compared in isogenic hsx1 and HSX1 strains. Thus, the HSX1 gene determines the ratio of the TYA1 to TYA1-TYB1 precursors required for protein processing or stability, and keeps expression of TYB1 a rate-limiting step in the retrotransposition cycle.

Role of Ethylene in the Biosynthesis of Fatty Acid-Derived Volatiles in Tomato Fruits

2011 ◽  
Vol 343-344 ◽  
pp. 937-950
Author(s):  
Yuan Hong Xie ◽  
Hong Yan Gao ◽  
Yun Bo Luo ◽  
Hong Xing Zhang ◽  
Xiang Ning Chen ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Linolenic Acid ◽  
Tomato Fruit ◽  
Ethylene Biosynthesis ◽  
Hydroperoxide Lyase ◽  
Wild Type ◽  
Tomato Fruits ◽  
Aroma Volatiles ◽  
Exogenous Ethylene

Regulation of ethylene biosynthesis or action has an important effect on volatiles production in tomato (Lycopersicon esculentum) fruits. To understand the role of ethylene in the biosynthesis of fatty acid-derived aroma volatiles in tomato, we used Lichun tomato from a transgenic line with strictly suppression of ethylene biosynthesis (antisenseLeACS2tomato) and its wild type background line. This study was focused on the levels of the precursor substrates, activities and transcriptional levels of aroma volatile-related enzymes, including lipoxygenase (LOX), hydroperoxide lyase (HPL) and alcohol dehydrogenase (ADH). We also investigated the different abilities of converting the precursor substrates to aroma volatiles in ethylene suppressed transgenic and wild-type (WT) tomato fruits. Our results showed that the contents of endogenous linoleic and linolenic acid in tomato fruits were ethylene depended. Suppression of ethylene biosynthesis increased the content of endogenous linolenic acid inLichuntomato fruit and then declined the ratio of linoleic /linolenic acid. Exogenous ethylene changed the value of linoleic acid /linolenic acid in antisenseLeACS2(ACS) tomato fruit to the similar level of WT. During the ripening of wild type Lichun tomato fruit, LOX activity was ethylene and development dependent. Suppression of ethylene biosynthesis did not inhibit the transcriptional expression ofLoxCgene. And the HPL and ADH activities were partial ethylene-dependent during the ripening of wild typeLichuntomato fruit. Moreover, suppression of ethylene biosynthesis also affected the bioconversion of unsaturated-fatty acid precursors to C6 aldehydes and C6 alcohols. All these results indicated that ethylene had complicated effects on the biosynthesis of fatty acid-derived armoa volatiles by affecting the precursor’s content, enzyme activities, enzyme expression and the substrate utilization.

scholarly journals Modulation of inhibition of ferrochelatase by N-methylprotoporphyrin

2006 ◽  
Vol 399 (1) ◽  
pp. 21-28 ◽  
Author(s):  
Zhen Shi ◽  
Gloria C. Ferreira
Keyword(s):  
Protoporphyrin Ix ◽  
Kinetic Mechanism ◽  
Wild Type ◽  
Rate Limiting Step ◽  
Transition State Analogue ◽  
Mammalian Cell Cultures ◽  
Kinetic Mechanisms ◽  
Specificity Constant ◽  
Order Of Magnitude ◽  
Rate Limiting

Protoporhyrin IX ferrochelatase catalyses the terminal step of the haem-biosynthetic pathway by inserting ferrous iron into protoporphyrin IX. NMPP (N-methylprotoporphyrin), a transition-state analogue and potent inhibitor of ferrochelatase, is commonly used to induce haem deficiency in mammalian cell cultures. To create ferrochelatase variants with different extents of tolerance towards NMPP and to understand further the mechanism of ferrochelatase inhibition by NMPP, we isolated variants with increased NMPP resistance, bearing mutations in an active-site loop (murine ferrochelatase residues 248–257), which was previously shown to mediate a protein conformational change triggered by porphyrin binding. The kinetic mechanisms of inhibition of two variants, in which Pro255 was replaced with either arginine (P255R) or glycine (P255G), were investigated and compared with that of wild-type ferrochelatase. While the binding affinity of the P255X variants for NMPP decreased by one order of magnitude in relation to that of wild-type enzyme, the inhibition constant increased by approximately two orders of magnitude (Kiapp values of 1 μM and 2.3 μM for P255R and P255G respectively, as against 3 nM for wild-type ferrochelatase). Nonetheless, the drastically reduced inhibition of the variants by NMPP was not paralleled with a decrease in specificity constant (kcat/Km, protoporhyrin IX) and/or catalytic activity (kcat). Further, although NMPP binding to either wild-type ferrochelatase or P255R occurred via a similar two-step kinetic mechanism, the forward and reverse rate constants associated with the second and rate-limiting step were comparable for the two enzymes. Collectively, these results suggest that Pro255 has a crucial role in maintaining an appropriate protein conformation and modulating the selectivity and/or regiospecificity of ferrochelatase.

Expression and functional analysis of PhEOL1 and PhEOL2 during flower senescence in petunia

2016 ◽  
Vol 43 (5) ◽  
pp. 413 ◽  
Author(s):  
Juanxu Liu ◽  
Ji Zhao ◽  
Zhina Xiao ◽  
Xinlei Chang ◽  
Guoju Chen ◽  
...  
Keyword(s):  
Petunia Hybrida ◽  
Ethylene Biosynthesis ◽  
Flower Senescence ◽  
Biosynthesis Pathway ◽  
Ethylene Treatment ◽  
Exogenous Ethylene ◽  
Rate Limiting ◽  
Two Hybrid

The ethylene biosynthesis pathway controls flower senescence. Previous studies have shown that Arabidopsis ETHYLENE-OVERPRODUCER1 (ETO1) interacts specifically with and negatively regulates type 2 1-aminocyclopropane-1-carboxylate synthases (ACSs), the rate-limiting enzymes of ethylene biosynthesis. The ethylene biosynthesis pathway controls flower senescence in petunias (Petunia hybrida Juss.). However, the role of ETO1-like genes (EOLs) during flower senescence has not been investigated. Here, two full-length petunia EOL cDNAs, PhEOL1 and PhEOL2, were isolated. RT–PCR assays indicated that the expression of PhEOL1 and PhEOL2 increased after exogenous ethylene treatment. The VIGS-mediated silencing of PhEOL1 accelerated flower senescence and produced more ethylene than the control condition, whereas the silencing of PhEOL2 did not. Notably, the effects caused by PhEOL1 suppression were not enhanced by PhEOL2 suppression in corollas. In addition, the expression of two petunia type 2 PhACS genes increased during flower senescence and after ethylene treatment. A yeast two-hybrid assay showed that PhEOL1 interacts with both PhACS2 and PhACS3. It is possible that PhEOL1 is involved in flower senescence by interacting with type 2 PhACSs in petunias.

scholarly journals Role of the glutamate 185 residue in proton translocation mediated by the proton-coupled folate transporter SLC46A1

2009 ◽  
Vol 297 (1) ◽  
pp. C66-C74 ◽  
Author(s):  
Ersin Selcuk Unal ◽  
Rongbao Zhao ◽  
I. David Goldman
Keyword(s):  
Proton Translocation ◽  
Amino Acid Residues ◽  
Loss Of Function ◽  
Wild Type ◽  
Folate Transport ◽  
Rate Limiting Step ◽  
Proximal Small Intestine ◽  
Transport Cycle ◽  
Rate Limiting

The proton-coupled folate transporter (PCFT) SLC46A1 mediates uphill folate transport into enterocytes in proximal small intestine coupled to the inwardly directed proton gradient. Hereditary folate malabsorption is due to loss-of-function mutations in the PCFT gene. This study addresses the functional role of conserved charged amino acid residues within PCFT transmembrane domains with a detailed analysis of the PCFT E185 residue. D156A-, E185A-, E232A-, R148A-, and R376A-PCFT mutants lost function at pH 5.5, as assessed by transient transfection in folate transport-deficient HeLa cells. At pH 7.4, function was preserved only for E185A-PCFT. Loss of function for E185A-PCFT at pH 5.5 was due to an eightfold decrease in the [3H]methotrexate (MTX) influx Vmax; the MTX influx Ktwas identical to that of wild-type (WT)-PCFT (1.5 μM). Consistent with the intrinsic functionality of E185A-PCFT, [3H]MTX influx at pH 5.5 or 7.4 was trans-stimulated in cells preloaded with nonlabeled MTX or 5-formyltetrahydrofolate. Replacement of E185 with Leu, Cys, His, or Gln resulted in a phenotype similar to E185A-PCFT. However, there was greater preservation of activity (∼38% of WT) for the similarly charged E185D-PCFT at pH 5.5. All E185 substitution mutants were biotin accessible at the plasma membrane at a level comparable to WT-PCFT. These observations suggest that the E185 residue plays an important role in the coupled flows of protons and folate mediated by PCFT. Coupling appears to have a profound effect on the maximum rate of transport, consistent with augmentation of a rate-limiting step in the PCFT transport cycle.

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