scholarly journals Diffusion Limitations in Root Uptake of Cadmium and Zinc, But Not Nickel, and Resulting Bias in the Michaelis Constant

2012 ◽  
Vol 160 (2) ◽  
pp. 1097-1109 ◽  
Author(s):  
Fien Degryse ◽  
Afsaneh Shahbazi ◽  
Liesbeth Verheyen ◽  
Erik Smolders
Keyword(s):  
Root Uptake ◽  
Michaelis Constant ◽  
Diffusion Limitations

scholarly journals Screening of Supports for the Immobilization of β-Glucosidase

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Joelise de Alencar Figueira ◽  
Fernanda Furlan Gonçalves Dias ◽  
Hélia Harumi Sato ◽  
Pedro Fernandes
Keyword(s):  
Catalytic Activity ◽  
Polyvinyl Alcohol ◽  
Sol Gel ◽  
Ph Stability ◽  
Activity Profile ◽  
Michaelis Constant ◽  
Diffusion Limitations ◽  
Two Systems ◽  
Selection Of

A set of supports were screened for the immobilization of a partially purified extract of β-glucosidase from Aspergillus sp. These supports, namely, Eupergit, Amberlite, alginate, gelatin, polyvinyl alcohol- (PVA-) based matrices (Lentikats), and sol-gel, have proved effective for the implementation of some other enzyme-based processes. The initial criterion for selection of promising supports prior to further characterization relied on the retention of the catalytic activity following immobilization. Based on such criterion, where immobilization in sol-gel and in Lentikats outmatched the remaining approaches, those two systems were further characterized. Immobilization did not alter the pH/activity profile, whereas the temperature/activity profile was improved when sol-gel support was assayed. Both thermal and pH stability were improved as a result of immobilization. An increase in the apparent KM (Michaelis constant) was observed following immobilization, suggesting diffusion limitations.

Modeling the Effects of Diffusion Limitations on Nitrogen-15 Isotope Dilution Experiments with Soil Aggregates

2003 ◽  
Vol 67 (2) ◽  
pp. 677-677
Author(s):  
John B. Cliff ◽  
Peter J. Bottomley ◽  
Roy Haggerty ◽  
David D. Myrold
Keyword(s):  
Isotope Dilution ◽  
Soil Aggregates ◽  
Diffusion Limitations ◽  
Dilution Experiments

Peroxidases from Tulip Bulbs (Tulipa fosteriana, L.) Oxidize Xenobiotics NNitrosodimethylamine and N-Nitroso-N-methylaniline in vitro

1997 ◽  
Vol 62 (11) ◽  
pp. 1804-1814 ◽  
Author(s):  
Marie Stiborová ◽  
Hana Hansíková
Keyword(s):  
Cytochromes P450 ◽  
Kinetic Studies ◽  
The Other ◽  
Maximal Velocity ◽  
Michaelis Constant ◽  
Other Hand ◽  
Plant Peroxidases ◽  
Tulip Bulbs

Tulip bulbs (Tulipa fosteriana, L.) contain peroxidases catalyzing the oxidation of the xenobiotics N-nitrosodimethylamine (NDMA) and N-nitroso-N-methylaniline (NMA). Three anionic (A1, A2, A3) and four cationic (B, C, D, E) peroxidases were purified from this tissue, partially characterized and used for kinetic studies. Demethylation of NDMA and NMA producing formaldehyde is catalyzed by one anionic (A1) and three cationic (C, D, E) peroxidases. The oxidation of NDMA by tulip peroxidases exhibits the Michaelis-Menten kinetics. The apparent Michaelis constant and the maximal velocity values for this substrate were determined. On the other hand, non-Michaelian kinetics for the NMA oxidation were observed with tulip peroxidases. The most abundant cationic peroxidase (peroxidase C) was used for detailed enzymatic studies. In addition to formation of formaldehyde, methylaniline, aniline, 4-aminophenol and phenol were found to be metabolites formed from NMA. Phenol was formed presumably by N-demethylation via a benzenediazonium ion, while methylaniline, aniline and 4-aminophenol were products of denitrosation of the substrate. The efficiencies of plant peroxidases to oxidize NDMA and NMA in vitro are compared with those of cytochromes P450 and discussed.

scholarly journals Structure-Properties Correlation of Cross-Linked Penicillin G Acylase Crystals

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 451
Author(s):  
Marta Kubiak ◽  
Janine Mayer ◽  
Ingo Kampen ◽  
Carsten Schilde ◽  
Rebekka Biedendieck
Keyword(s):  
Mechanical Stability ◽  
Structural Characteristics ◽  
Penicillin G ◽  
Bacillus Species ◽  
Diffusion Limitations ◽  
Small Water ◽  
Long Term Stability ◽  
Atomic Force ◽  
First Time

In biocatalytic processes, the use of free enzymes is often limited due to the lack of long-term stability and reusability. To counteract this, enzymes can be crystallized and then immobilized, generating cross-linked enzyme crystals (CLECs). As mechanical stability and activity of CLECs are crucial, different penicillin G acylases (PGAs) from Gram-positive organisms have proven to be promising candidates for industrial production of new semisynthetic antibiotics, which can be crystallized and cross-linked to characterize the resulting CLECs regarding their mechanical and catalytic properties. The greatest hardness and Young’s modulus determined by indentation with an atomic force microscope were observed for CLECs of Bacillus species FJAT-PGA CLECs (26 MPa/1450 MPa), followed by BmPGA (Priestia megaterium PGA, 23 MPa/1170 MPa) and BtPGA CLECs (Bacillus thermotolerans PGA, 11 MPa/614 MPa). In addition, FJAT- and BtPGA CLECs showed up to 20-fold higher volumetric activities compared to BmPGA CLECs. Correlation to structural characteristics indicated that a high solvent content and low number of cross-linking residues might lead to reduced stability. Furthermore, activity seems to be restricted by small water channels due to severe diffusion limitations. To the best of our knowledge, we show for the first time in this study that the entire process chain for the characterization of diverse industrially relevant enzymes can be performed at the microliter scale to discover the most important relationships and limitations.

scholarly journals Publisher Correction: Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yasunori Mahara ◽  
Tomoko Ohta ◽  
Jyunichi Ohshima ◽  
Kazuya Iizuka
Keyword(s):  
Soil Water ◽  
Xylem Sap ◽  
Root Uptake

scholarly journals Per- and polyfluoroalkyl substances (PFASs) in the soil–plant system: Sorption, root uptake, and translocation

2021 ◽  
Vol 156 ◽  
pp. 106642
Author(s):  
Weiping Mei ◽  
Hao Sun ◽  
Mengke Song ◽  
Longfei Jiang ◽  
Yongtao Li ◽  
...  
Keyword(s):  
Root Uptake ◽  
Plant System ◽  
Polyfluoroalkyl Substances

scholarly journals Development of a Bioartificial Vascular Pancreas

2021 ◽  
Vol 12 ◽  
pp. 204173142110277
Author(s):  
Edward X Han ◽  
Juan Wang ◽  
Mehmet Kural ◽  
Bo Jiang ◽  
Katherine L Leiby ◽  
...  
Keyword(s):  
Type 1 Diabetes ◽  
Pancreatic Islets ◽  
Vascular Graft ◽  
Term Treatment ◽  
Diffusion Limitations ◽  
Human Scale ◽  
Arterial Blood ◽  
Long Term Treatment

Transplantation of pancreatic islets has been shown to be effective, in some patients, for the long-term treatment of type 1 diabetes. However, transplantation of islets into either the portal vein or the subcutaneous space can be limited by insufficient oxygen transfer, leading to islet loss. Furthermore, oxygen diffusion limitations can be magnified when islet numbers are increased dramatically, as in translating from rodent studies to human-scale treatments. To address these limitations, an islet transplantation approach using an acellular vascular graft as a vascular scaffold has been developed, termed the BioVascular Pancreas (BVP). To create the BVP, islets are seeded as an outer coating on the surface of an acellular vascular graft, using fibrin as a hydrogel carrier. The BVP can then be anastomosed as an arterial (or arteriovenous) graft, which allows fully oxygenated arterial blood with a pO2 of roughly 100 mmHg to flow through the graft lumen and thereby supply oxygen to the islets. In silico simulations and in vitro bioreactor experiments show that the BVP design provides adequate survivability for islets and helps avoid islet hypoxia. When implanted as end-to-end abdominal aorta grafts in nude rats, BVPs were able to restore near-normoglycemia durably for 90 days and developed robust microvascular infiltration from the host. Furthermore, pilot implantations in pigs were performed, which demonstrated the scalability of the technology. Given the potential benefits provided by the BVP, this tissue design may eventually serve as a solution for transplantation of pancreatic islets to treat or cure type 1 diabetes.

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