Anatomy, Biochemistry and Physiology
Massimo Maffei in Vetiveria, 2002
The primary carboxylation reaction, common to all three variants, occurs in the cytosol of the mesophyll cells and is catalysed by phosphoenolpyruvate carboxylase (PEP-case), using HCO3− rather than CO2 as a substrate. The fate of the oxaloacetate produced in this reaction depends on the C4 variant (Gutierrez et al., 1974). In the NADP-ME type, oxaloacetate is reduced to malate in the mesophyll chloroplasts, then transported to the bundle sheath cell chloroplasts and decarboxylated by NADP-ME enzyme. In the NAD-ME and PCK species, oxaloacetate undergoes transamination in the cytosol with glutamate as amino donor. The aspartate is transported into the bundle sheath cells and reconverted to oxaloacetate by transamination in the mitochondria (NAD-ME species) or the cytosol (PCK species). Without changing compartmentalization, the oxaloacetate is reduced and then decarboxylated by NAD-ME in NAD-ME species, while in PCK species oxaloacetate is decarboxylated by PCK. In NADP-ME plants, the C3 acid transported back to the mesophyll is pyruvic acid as pyruvate but in NAD-ME and PCK species alanine is probably converted to pyruvate in the mesophyll cell cytosol. The final reaction of the C4 pathway, which is common to all three variants, is the conversion of pyruvate to phosphoenolpyruvate within the mesophyll chloroplasts (Maffei, 1999).
The Reaction Mechanism
D. B. Keech, J. C. Wallace in Pyruvate Carboxylase, 2018
In 1965, Retey and Lynen681 proposed that the transfer of the carboxyl group from carboxybiotin to propionyl-CoA, as catalyzed by propionyl-CoA carboxylase, occurred by a concerted reaction involving a six-membered ring complex (Structure I). This proposal was based on their finding that carboxylation of propionyl-CoA occurs with retention of configuration, i.e., a proton is removed from the substrate and the carboxyl group is added to the same face. Later, Prescott and Rabinowitz658 obtained data which were consistent with the proposed mechanism. They found that the rate of release of 3H from [2-3H] propionyl-CoA was the same as the rate of the overall reaction. Furthermore, 3H from 3H2O was not incorporated into propionyl-CoA in the absence of the reverse reaction.
Vaccinia Virus as a Carrier of Vaccine Antigens
F. Y. Liew in Vaccination Strategies of Tropical Diseases, 2017
An advantage of using a eukaryotic viral vector to express a eukaryotic gene is the probability that the protein will be normally modified and transported within the cell. Vaccinia virus-infected cells modify and transport foreign proteins normally as a general rule. However, there are a few specific examples where there are differences. There is ample evidence showing that expression of foreign glycoprotein genes in vaccinia virus yields proteins with similar electrophoretic mobilities to the authentic gene product.60-82 Glycosylation and proteolytic cleavage both occur,68 although in some cases the proteolytic cleavage is dependent upon the cell line chosen70 or the presence of exogenous trypsin.61 Even in cases where multiple forms of glycoprotein appear from the same gene, the forms produced by vaccinia virus recombinants match those of the protein synthesized during infection in its natural host.68,81 Carboxylation of an expressed gene has also been reported.83
Quantitation of cell-associated carbon nanotubes: selective binding and accumulation of carboxylated carbon nanotubes by macrophages
Published in Nanotoxicology, 2018
Ruhung Wang, Michael Lee, Karina Kinghorn, Tyler Hughes, Ishwar Chuckaree, Rishabh Lohray, Erik Chow, Paul Pantano, Rockford Draper
The common denominator enhancing accumulation appears to be MWNT carboxylation. To see if this trend could be extended to SWNTs, the accumulation of P-SWNTs and C-SWNTs [CNT suspension samples (i) and (j) in Table 2] by A549 and RAW 264.7 cells were compared (Figure 4(B)). P-SWNTs were not significantly accumulated at either 100 or 200 µg/mL by A549 cells; however, C-SWNTs at 200 µg/mL were accumulated more than P-SWNTs by A549 cells, trends similar to P-MWNTs and C-MWNTs with this non-macrophage cell line. These parallel observations continued with RAW 264.7 cells where there was low accumulation of P-SWNTs but a high accumulation of C-SWNTs that was dose dependent (Figure 4(B)). The quantitation of cell-associated SWNTs by the SDS-PAGE method was verified by an independent technique based on the distinctive SWNT Raman scattering signal, as described in the Supplemental Methods and Figure S4. Thus, both the SDS-PAGE optical scanning and the Raman spectroscopy techniques provided evidence for the selective accumulation of C-SWNTs over P-SWNTs in macrophages. P-SWNTs were not significantly toxic to RAW 264.7 cells, although proliferation was mildly reduced by C-SWNTs at 200 µg/mL, the highest concentration tested (Figure S3(B)). We previously noted that the toxicity of this preparation of C-SWNTs correlates with the presence of oxidative debris fragments, not with the intact C-SWNTs themselves (Wang et al. 2011). Thus, the differential toxicity of P-SWNTs is not likely a factor in its low accumulation compared to C-SWNTs.
Lung deposition patterns of MWCNT vary with degree of carboxylation
Published in Nanotoxicology, 2019
Andrij Holian, Raymond F. Hamilton, Zhequion Wu, Sanghamitra Deb, Kevin L. Trout, Zhiqian Wang, Rohit Bhargava, Somenath Mitra
Based on our prior experience and that from a number of other laboratories (Hamilton et al. 2013a, 2013b, 2018; Li et al. 2013; Sweeney et al. 2016), we proposed that carboxylation would decrease toxicity and in vivo inflammation. Since suspension of carboxylated MWCNT results in smaller agglomerates than unmodified MWCNT, we anticipated that there would be better dispersion following instillation. What was less clear was whether there would differences in the cell types that the carboxylated MWCNT would be interacting with and how that might affect clearance of carboxylated MWCNT compared to unmodified MWCNT. In order to have more confidence in detecting the presence of smaller agglomerates in the lungs, two approaches were used. Both CytoViva (SFF method) and Raman (SRS) imaging gave similar results and detected MWCNT with few false positives. There was a quite high signal-to-noise ratio when comparing the minimal background in control tissues versus the high signal in particle-exposed tissues, which indicates a high specificity of these methods for detection of MWCNT. SFF provided better images of tissues to observe in which cell the particles were present, while SRS provided higher resolution of each individual particle and captured a larger area of the lung section. Therefore, both methods were complementary for general observation of tissue localization and particle resolution for quantification.
Inhibition of α-, β-, γ-, δ-, ζ- and η-class carbonic anhydrases from bacteria, fungi, algae, diatoms and protozoans with famotidine
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Andrea Angeli, Mariana Pinteala, Stelian S. Maier, Sonia Del Prete, Clemente Capasso, Bogdan C. Simionescu, Claudiu T. Supuran
Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous metalloenzymes all over the phylogenetic tree, with seven distinct genetic families described so far, the α-, β-, γ-, δ-, ζ-, η- and Θ-CAs1–13, and the probability to discover other such families is quite high. This is mainly due to the fact that these enzymes catalyse a simple but essential chemical reaction, the interconversion of carbon dioxide and water, with formation of bicarbonate and protons: CO2+H2O ⇌ HCO3–+H+1,14–18. In tissues/organisms where CAs are present, they are involved in pH regulation (a tightly controlled process in all living organisms) and metabolic processes connected to carboxylation/decarboxylation reactions1–13. In plants and some bacteria (e.g. cyanobacteria), CAs also play a function in photosynthesis, for example assuring a carbon concentrating mechanism (CCM) which enhances the concentration of CO2 available for 1,5-bisphosphate carboxylase/oxygenase (RUBISCO)19–22. Diatoms are also encoding for several classes of CAs. In fact, the δ- and ζ-CAs were discovered in these organisms4,6, in which they probably play essential functions, poorly understood at this moment21.
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