THE FORMATION OF CELLULOSE MICROFIBRILS BY ACETOBACTER XYLINUM IN AGAR SURFACES

1961 ◽  
Vol 7 (3) ◽  
pp. 383-387 ◽  
Author(s):  
B. Millman ◽  
J. Ross Colvin
Keyword(s):  
Activation Energy ◽  
Cell Membrane ◽  
Characteristic Feature ◽  
Acetobacter Xylinum ◽  
Cellulose Microfibrils ◽  
High Polymer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Liquid Suspensions ◽  
Rate Limiting

The formation of extracellular cellulose microfibrils by Acetobacter xylinum on agar surfaces is remote from the cell membrane and does not involve an intermediate, amorphous high polymer, in agreement with conclusions from studies of liquid suspensions. Growth of individual microfibrils is at the tip(s) only and the rate of extension (0.2 μ per bacterial cell per minute at 34 °C) is comparable with that in liquid medium. The rate of nucleation of new microfibrils is about 40 per 103 bacteria per minute at 34 °C. Both rates are constant after an induction period of about 30 seconds. Newly nucleated microfibrils could be identified unequivocally down to a length of 0.5 μ. A characteristic feature of growth of cellulose on agar surfaces is the formation of bundles of microfibrils with their axes roughly parallel. The results suggest that the rate-limiting step in the formation of these microfibrils has an activation energy of about 15 kc.

scholarly journals Study on the Adsorption Kinetics of Acid Red 3B on Expanded Graphite

2008 ◽  
Vol 5 (4) ◽  
pp. 802-809 ◽  
Author(s):  
Xiu-yan Pang ◽  
Fei Gong
Keyword(s):  
Activation Energy ◽  
Adsorption Kinetics ◽  
Adsorption Process ◽  
Expanded Graphite ◽  
Chemical Oxidation ◽  
Adsorption Rate ◽  
Order Kinetic ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Expanded graphite (EG) is a kind of important adsorbent for organic compound such as oil and dyes. We have investigated the adsorption kinetics characteristics of this adsorbent for dye. EG was prepared with 50 mesh crude graphite through chemical oxidation intercalation of potassium permanganate and vitriol, and dye of acid red 3B was used as model sorbate. We have studied the adsorption kinetic models and rate-limiting step of the process. Adsorption rate and activation energy of the adsorption process were calculated. Kinetic studies show that the kinetic data are well described by the pseudo second-order kinetic model. The equilibrium adsorbance increases with the increase of the initial acid red 3B concentration. Initial adsorption rate increases with the increase of the initial dye concentration and temperature. Adsorption process of acid red 3B on EG has small activation energy. Internal diffusion appears to be the rate-limiting step for the adsorption process.

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

Single-Molecular Catalysis Identifying Activation Energy of the Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

Nano Letters ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 2507-2513 ◽  
Author(s):  
Wei Li ◽  
Junjian Miao ◽  
Tianhuan Peng ◽  
Hui Lv ◽  
Jun-Gang Wang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Intermediate Product ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Molecular Catalysis ◽  
Rate Limiting

THE UPTAKE OF GLUCOSE INTO CELLS AND THE ROLE OF INSULIN IN GLUCOSE TRANSPORT

1964 ◽  
Vol 42 (6) ◽  
pp. 933-944 ◽  
Author(s):  
Margaret J. Henderson
Keyword(s):  
Cell Membrane ◽  
Glucose Uptake ◽  
Glucose Transport ◽  
Glucose Levels ◽  
Insulin Transport ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Extracellular Glucose ◽  
Rate Limiting

This presentation has been restricted to the role of insulin in glucose transport in muscle cells and deals mainly with experiments using the perfused rat heart. The several possible means for glucose transfer into cells, diffusion, pores, pinocytosis, carriers, and dimerization, have been discussed; and arguments in favor of the carrier theory, namely, specificity, kinetics, inhibition, competition, and counterflow, have been elaborated. Glucose uptake has been considered to consist of three sequential steps: (1) passage of glucose from within the capillary to the cell surface, (2) transport across the cell membrane, and (3) metabolism of glucose within the cell. The first is considered to take place by diffusion and not to be significantly limiting under normal conditions, nor to be influenced by insulin. Transport across the cell membrane is thought to be mainly under the control of insulin and is the major rate-limiting step in glucose uptake when the extracellular glucose levels are in the normal range. Metabolism of glucose within the cell is the major rate-limiting step in glucose uptake when intracellular glucose concentration is so high that its phosphorylation is near saturation.

scholarly journals Is the Cell Membrane a Universal Rate-Limiting Barrier to the Movement of Water between the Living Cell and Its Surrounding Medium?

1967 ◽  
Vol 50 (6) ◽  
pp. 1807-1820 ◽  
Author(s):  
Gilbert N. Ling ◽  
Margaret M. Ochsenfeld ◽  
George Karreman
Keyword(s):  
Cell Membrane ◽  
Living Cell ◽  
Profile Analysis ◽  
Surrounding Medium ◽  
Tritiated Water ◽  
Intracellular Water ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

With the use of a newly introduced technique, the "influx profile analysis," we studied the diffusion of tritiated water in and out of frog ovarian eggs at 25°C. The results show that the rate-limiting step in the exchange of labeled water is not permeation through the cell membrane but diffusion in the bulk of the intracellular water.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
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