scholarly journals Role of Metabolites in the Reversible Light Activation of Pyruvate, Orthophosphate Dikinase in Zea mays Mesophyll Cells in Vivo

1989 ◽  
Vol 90 (1) ◽  
pp. 330-337 ◽  
Author(s):  
Chrissl A. Roeske ◽  
Raymond Chollet
Keyword(s):  
Zea Mays ◽  
Light Activation ◽  
Mesophyll Cells ◽  
Pyruvate Orthophosphate Dikinase ◽  
Orthophosphate Dikinase

scholarly journals Substrate specificity and regulation of the maize (Zea mays) leaf ADP: protein phosphotransferase catalysing phosphorylation/inactivation of pyruvate, orthophosphate dikinase

1986 ◽  
Vol 236 (2) ◽  
pp. 579-584 ◽  
Author(s):  
R J A Budde ◽  
S M Ernst ◽  
R Chollet
Keyword(s):  
Zea Mays ◽  
Substrate Specificity ◽  
Regulatory Protein ◽  
Energy Charge ◽  
Adenylate Energy Charge ◽  
Protein Substrate ◽  
Maize Leaf ◽  
Pyruvate Orthophosphate Dikinase ◽  
Orthophosphate Dikinase ◽  
Regulatory Phosphorylation

The protein substrate specificity of the maize (Zea mays) leaf ADP: protein phosphotransferase (regulatory protein, RP) was studied in terms of its relative ability to inactivate/phosphorylate pyruvate, orthophosphate dikinase from Zea mays and the non-sulphur purple photosynthetic bacterium Rhodospirillum rubrum. The dimeric bacterial dikinase was inactivated by the maize leaf RP via phosphorylation, with a stoichiometry of approximately 1 mol of phosphate incorporated/mol of 92.7-kDa protomer. Inactivation required both ADP and ATP, with ADP being the specific donor for regulatory phosphorylation. The requirements for inactivation/phosphorylation in this heterologous system were identical with those previously established for the tetrameric maize leaf dikinase. The ADP-dependent maize leaf RP did not phosphorylate alternative protein substrates such as casein or phosvitin, and its activity was not affected by cyclic nucleotides, Ca2+ or calmodulin. The regulation of the maize leaf ADP: protein phosphotransferase was studied in terms of changes in adenylate energy charge and pyruvate concentration. The change in adenylate energy charge necessary to substantially inhibit phosphorylation of maize leaf dikinase was not suggestive of it being a physiological modulator of phosphotransferase activity. Pyruvate was a potent competitive inhibitor of regulatory phosphorylation (Ki = 80 microM), consistent with its interaction with the catalytic phosphorylated intermediate of dikinase, the true protein substrate for ADP-dependent phosphorylation/inactivation.

Phosphoenolpyruvate carboxylase mediated carbon flow in a cyanobacterium

1988 ◽  
Vol 66 (2) ◽  
pp. 93-99 ◽  
Author(s):  
George W. Owttrim ◽  
Brian Colman
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Protein Production ◽  
Carbon Fixation ◽  
Fixed Carbon ◽  
Free System ◽  
Pyruvate Orthophosphate Dikinase ◽  
Orthophosphate Dikinase ◽  
Phosphoglyceric Acid ◽  
A Cell

The source of the substrate phosphoenolpyruvate (PEP) for phosphoenolpyruvate carboxylase (PEP-case) activity in the cyanobacterium Coccochloris peniocystis has been investigated, as well as possible sinks for this carbon. PEP was not produced by pyruvate orthophosphate dikinase, as this activity was not detectable in cell-free lysates. PEP is supplied from photosynthetically or glycolytically produced 3-phosphoglyceric acid (3-PGA), as carbon was observed to flow from 3-PGA to C4 acids in a cell-free system. This indicates PEP-case activity is dependent on photosynthetically fixed carbon and thus two separate carbon fixation reactions occur in the cell in the light. Estimates of the in vivo concentrations of various metabolites indicates that neither substrate nor inhibitor concentrations limit enzyme activity in vivo. Thus PEP-case activity in vivo appears to be limited by the supply of PEP and is, therefore, high in the light and low in the dark. The nitrogen storage product cyanophycin was identified as one sink for carbon fixed by PEP-case. As a culture aged, cyanophycin production increased, while chlorophyll and protein production decreased.

scholarly journals Deep Imaging Analysis in VISUAL Reveals the Role of YABBY Genes in Vascular Stem Cell Fate Determination

2020 ◽  
Vol 61 (2) ◽  
pp. 255-264
Author(s):  
Alif Meem Nurani ◽  
Yasuko Ozawa ◽  
Tomoyuki Furuya ◽  
Yuki Sakamoto ◽  
Kazuo Ebine ◽  
...  
Keyword(s):  
Stem Cells ◽  
Cell Fate ◽  
Spatial Information ◽  
Secondary Growth ◽  
Vascular Differentiation ◽  
Mesophyll Cells ◽  
Vascular Cell

Abstract Stem cells undergo cell division and differentiation to ensure organized tissue development. Because plant cells are immobile, plant stem cells ought to decide their cell fate prior to differentiation, to locate specialized cells in the correct position. In this study, based on a chemical screen, we isolated a novel secondary cell wall indicator BF-170, which binds to lignin and can be used to image in vitro and in situ xylem development. Use of BF-170 to observe the vascular differentiation pattern in the in vitro vascular cell induction system, VISUAL, revealed that adaxial mesophyll cells of cotyledons predominantly generate ectopic xylem cells. Moreover, phloem cells are abundantly produced on the abaxial layer, suggesting the involvement of leaf adaxial–abaxial polarity in determining vascular cell fate. Analysis of abaxial polarity mutants highlighted the role of YAB3, an abaxial cell fate regulator, in suppressing xylem and promoting phloem differentiation on the abaxial domains in VISUAL. Furthermore, YABBY family genes affected in vivo vascular development during the secondary growth. Our results denoted the possibility that such mediators of spatial information contribute to correctly determine the cell fate of vascular stem cells, to conserve the vascular pattern of land plants.

scholarly journals Phosphorylation of a stromal enzyme protein in maize (Zea mays) mesophyll chloroplasts

1984 ◽  
Vol 222 (1) ◽  
pp. 247-253 ◽  
Author(s):  
C Foyer
Keyword(s):  
Zea Mays ◽  
Sodium Dodecyl Sulphate ◽  
Gel Electrophoresis ◽  
Co2 Fixation ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Polyacrylamide Gel ◽  
Pyruvate Orthophosphate Dikinase ◽  
Carbon Compound ◽  
Orthophosphate Dikinase

When intact maize (Zea mays) mesophyll chloroplasts were illuminated in the presence of [32P]orthophosphate and subsequently subjected to sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, a major polypeptide species of Mr 100000 was found to be heavily labelled. This polypeptide was not found in maize mesophyll thylakoid or cytoplasmic fractions, but was localized solely in the chloroplast stroma. No phosphorylation of polypeptides in the 100000-Mr region was observed in the mesophyll chloroplasts from C3 species (where the primary product of CO2 fixation is a 3-carbon compound), suggesting that this polypeptide arises from a protein associated with C4 metabolism (where the first product of CO2 fixation is a 4-carbon compound). The 100kDa polypeptide was major component of the maize mesophyll chloroplast, comprising 10-15% of the total protein, which banded in an identical position to the apoprotein of the enzyme pyruvate, orthophosphate dikinase, which catalyses a reaction of the C4 cycle [Edwards & Walker (1983) C3, C4: Mechanisms, and Cellular and Environmental Regulation, of Photosynthesis, Blackwell Scientific Publications, Oxford and London]. Phosphorylation in the 100kDa species was prohibited by treatment of lysed chloroplasts with antibody to pyruvate, orthophosphate dikinase (EC 2.7.9.1). These data suggest that the phosphorylated polypeptide observed after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis is the monomeric form of this enzyme. The 100kDa polypeptide was partially phosphorylated in darkness, but a significant increase in the degree of phosphorylation was found on illumination. This polypeptide was found to be dephosphorylated only slowly when the chloroplasts were returned to darkness. Maximum phosphorylation was observed in the presence of pyruvate or dihydroxyacetone phosphate, which also caused maximum activation of pyruvate, orthophosphate dikinase. Phosphorylation of the 100kDa polypeptide did not coincide with deactivation of pyruvate, orthophosphate dikinase, but maximum phosphorylation occurred under conditions that promoted maximum activity of the enzyme, at which time one phosphate group was associated with each enzyme molecule. Protein phosphorylation did not appear to arise from the reaction mechanism of the enzyme.

Mitochondrial matrix calcium ions regulate energy production in myocardium: A cytochemical study

1990 ◽  
Vol 48 (2) ◽  
pp. 166-167
Author(s):  
W.A. Jacob ◽  
R. Hertsens ◽  
A. Van Bogaert ◽  
M. De Smet
Keyword(s):  
Energy Metabolism ◽  
Calcium Ions ◽  
Energy Production ◽  
Regulation Of Respiration ◽  
Free Calcium ◽  
Mitochondrial Matrix ◽  
Cytochemical Study ◽  
Nmr Techniques

In the past most studies of the control of energy metabolism focus on the role of the phosphorylation potential ATP/ADP.Pi on the regulation of respiration. Studies using NMR techniques have demonstrated that the concentrations of these compounds for oxidation phosphorylation do not change appreciably throughout the cardiac cycle and during increases in cardiac work. Hence regulation of energy production by calcium ions, present in the mitochondrial matrix, has been the object of a number of recent studies.Three exclusively intramitochondnal dehydrogenases are key enzymes for the regulation of oxidative metabolism. They are activated by calcium ions in the low micromolar range. Since, however, earlier estimates of the intramitochondnal calcium, based on equilibrium thermodynamic considerations, were in the millimolar range, a physiological correlation was not evident. The introduction of calcium-sensitive probes fura-2 and indo-1 made monitoring of free calcium during changing energy metabolism possible. These studies were performed on isolated mitochondria and extrapolation to the in vivo situation is more or less speculative.

Meiotic CENP-C is a shepherd: bridging the space between the centromere and the kinetochore in time and space

2020 ◽  
Vol 64 (2) ◽  
pp. 251-261
Author(s):  
Jessica E. Fellmeth ◽  
Kim S. McKim
Keyword(s):  
Chromosome Segregation ◽  
New Technologies ◽  
Early Prophase ◽  
Unique Role ◽  
Kinetochore Assembly ◽  
M Phase ◽  
In Vivo Analysis ◽  
Meiosis I

Abstract While many of the proteins involved in the mitotic centromere and kinetochore are conserved in meiosis, they often gain a novel function due to the unique needs of homolog segregation during meiosis I (MI). CENP-C is a critical component of the centromere for kinetochore assembly in mitosis. Recent work, however, has highlighted the unique features of meiotic CENP-C. Centromere establishment and stability require CENP-C loading at the centromere for CENP-A function. Pre-meiotic loading of proteins necessary for homolog recombination as well as cohesion also rely on CENP-C, as do the main scaffolding components of the kinetochore. Much of this work relies on new technologies that enable in vivo analysis of meiosis like never before. Here, we strive to highlight the unique role of this highly conserved centromere protein that loads on to centromeres prior to M-phase onset, but continues to perform critical functions through chromosome segregation. CENP-C is not merely a structural link between the centromere and the kinetochore, but also a functional one joining the processes of early prophase homolog synapsis to late metaphase kinetochore assembly and signaling.

The Role of Polyphenols in the Modulation of Plasma Non-Enzymatic Antioxidant Capacity (NEAC)

2012 ◽  
Vol 82 (3) ◽  
pp. 228-232 ◽  
Author(s):  
Mauro Serafini ◽  
Giuseppa Morabito
Keyword(s):  
Antioxidant Capacity ◽  
Dietary Intervention ◽  
Ex Vivo ◽  
The Body ◽  
Dietary Polyphenols ◽  
Enzymatic Antioxidant ◽  
Endogenous Antioxidant

Dietary polyphenols have been shown to scavenge free radicals, modulating cellular redox transcription factors in different in vitro and ex vivo models. Dietary intervention studies have shown that consumption of plant foods modulates plasma Non-Enzymatic Antioxidant Capacity (NEAC), a biomarker of the endogenous antioxidant network, in human subjects. However, the identification of the molecules responsible for this effect are yet to be obtained and evidences of an antioxidant in vivo action of polyphenols are conflicting. There is a clear discrepancy between polyphenols (PP) concentration in body fluids and the extent of increase of plasma NEAC. The low degree of absorption and the extensive metabolism of PP within the body have raised questions about their contribution to the endogenous antioxidant network. This work will discuss the role of polyphenols from galenic preparation, food extracts, and selected dietary sources as modulators of plasma NEAC in humans.

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