scholarly journals Energy-dependence of calcium accumulation during sporulation of Bacillus megaterium KM

1979 ◽  
Vol 178 (3) ◽  
pp. 627-632 ◽  
Author(s):  
C Hogarth ◽  
D J Ellar
Keyword(s):  
Cell Membrane ◽  
Active Transport ◽  
Bacillus Megaterium ◽  
Mother Cell ◽  
Adenosine Triphosphatase ◽  
Nadh Oxidase ◽  
Endogenous Respiration ◽  
Facilitated Diffusion ◽  
Carbonyl Cyanide ◽  
Active Transport Process

Ca2+ accumulation and endogenous respiration of sporulating Bacillus megaterium are inhibited to the same extent by electron-transport of inhibitors and the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone, suggesting that Ca2+ is accumulated by an active transport process. Forespores isolated in stage V of sporulation demonstrated Ca2+-specific carrier-mediated Ca2+ uptake, consistent with downhill transfer [Hogarth & Ellar (1978) Biochem. J. 176, 197-203]. In the present studies forespore Ca2+ uptake was unaffected by carbonyl cyanide p-trifluoromethoxyphenylhydrazone and by concentrations of respiratory inhibitor that inhibited forespore endogenous respiration by 85%. These data suggest that Ca2+ enters the isolated forespore by facilitated diffusion. Ca2+ uptake into sporulating protoplasts was completely inhibited by concentrations of respiratory inhibitors that had no effect on either Ca2+ uptake or respiration of stage-V forespores, but which resulted in inhibition of mother-cell membrane NADH oxidase. These results indicate that the mother-cell membrane is a site for active transport of Ca2+ into the sporulating cell. The effects of the adenosine triphosphatase inhibitor dicyclohexylcarbodi-imide on mother-cell membrane adenosine triphosphatase, NADH oxidase and protoplast Ca2+ uptake were examined.

scholarly journals Uptake of l-nicotine and of 6-hydroxy-l-nicotine by Arthrobacter nicotinovorans and by Escherichia coli is mediated by facilitated diffusion and not by passive diffusion or active transport

Microbiology ◽  
2009 ◽  
Vol 155 (6) ◽  
pp. 1866-1877 ◽  
Author(s):  
Petra Ganas ◽  
Roderich Brandsch
Keyword(s):  
Escherichia Coli ◽  
Cell Membrane ◽  
Active Transport ◽  
Passive Diffusion ◽  
Amino Acid Transporters ◽  
Facilitated Diffusion ◽  
Oxidase Gene ◽  
Nicotine Concentration ◽  
Nicotine Derivatives ◽  
Arthrobacter Nicotinovorans

The mechanism by which l-nicotine is taken up by bacteria that are able to grow on it is unknown. Nicotine degradation by Arthrobacter nicotinovorans, a Gram-positive soil bacterium, is linked to the presence of the catabolic megaplasmid pAO1. l-[14C]Nicotine uptake assays with A. nicotinovorans showed transport of nicotine across the cell membrane to be energy-independent and saturable with a K m of 6.2±0.1 μM and a V max of 0.70±0.08 μmol min−1 (mg protein)−1. This is in accord with a mechanism of facilitated diffusion, driven by the nicotine concentration gradient. Nicotine uptake was coupled to its intracellular degradation, and an A. nicotinovorans strain unable to degrade nicotine (pAO1−) showed no nicotine import. However, when the nicotine dehydrogenase genes were expressed in this strain, import of l-[14C]nicotine took place. A. nicotinovorans pAO1− and Escherichia coli were also unable to import 6-hydroxy-l-nicotine, but expression of the 6-hydroxy-l-nicotine oxidase gene allowed both bacteria to take up this compound. l-Nicotine uptake was inhibited by d-nicotine, 6-hydroxy-l-nicotine and 2-amino-l-nicotine, which may indicate transport of these nicotine derivatives by a common permease. Attempts to correlate nicotine uptake with pAO1 genes possessing similarity to amino acid transporters failed. In contrast to the situation at the blood–brain barrier, nicotine transport across the cell membrane by these bacteria was not by passive diffusion or active transport but by facilitated diffusion.

scholarly journals Morphofunctional characteristic of the unstirred water layer intestinal epithelium and its role in absorption/bioavailability of drugs (literature review)

2021 ◽  
pp. 29-37
Author(s):  
Mykola Golovenko
Keyword(s):  
Energy Consumption ◽  
Active Transport ◽  
Intestinal Epithelium ◽  
Molecular Mechanisms ◽  
Water Layer ◽  
Facilitated Diffusion ◽  
Enzymatic System ◽  
Membrane Diffusion ◽  
Unstirred Water Layer ◽  
Active Transport Process

The aim of the article – analysis of the main morphological and functional characteristics of intestine epithelium unstirred water layer (UWL) and its role in molecular mechanisms of absorption/bioavailability of orally administered drugs. The method of UWL thickness determination based on effective permeability (Peff) values under various speed of intestinal perfusion flow as well as this indicator importance for solutions absorption determination there was also discussed the process of drugs is discussed absorption in the gastrointestinal tract which is provided by such physical processes as passive diffusion, facilitated diffusion and active transport, involving the UWL, membranes and endothelial tight junctions. The diffusion of small molecules to the cytoplasm is a rather fast process, thus passive transcellular permeability is determined by only the intestinal apical membrane diffusion. The mechanisms of transcellular and paracellular drugs transport in the intestinal epithelium are described. The possible molecular mechanisms of drugs molecules permeability by facilitated diffusion without energy consumption with channel formers and transfer proteins are discussed. The attention was to the active transport process through the enterocyte membrane with the help of transporters against the concentration gradient which is fulfilled with energy consumption due to ATP or other energy supplies. The classification of such transporters is given based an the transport direction (inside the cell – influx, or out off the cell – efflux) and regarding the organic substance transferred. The role of enterocyte enzymatic system CYP3A4 in drugs metabolism processes regulation is mentioned, which can influence their bioavailability. Key words: drugs, absorption, intestine epithelium, unstirred water layer, entherocyte, transcellular transport, intercellular transport

A nuclear localization signal can enhance both the nuclear transport and expression of 1 kb DNA

1999 ◽  
Vol 112 (12) ◽  
pp. 2033-2041
Author(s):  
J.J. Ludtke ◽  
G. Zhang ◽  
M.G. Sebestyen ◽  
J.A. Wolff
Keyword(s):  
Active Transport ◽  
Nuclear Localization ◽  
Transport Process ◽  
Nuclear Transport ◽  
Passive Diffusion ◽  
Viral Gene ◽  
Nuclear Localization Signals ◽  
Size Limit ◽  
Cytosolic Extract ◽  
Active Transport Process

Although the entry of DNA into the nucleus is a crucial step of non-viral gene delivery, fundamental features of this transport process have remained unexplored. This study analyzed the effect of linear double stranded DNA size on its passive diffusion, its active transport and its NLS-assisted transport. The size limit for passive diffusion was found to be between 200 and 310 bp. DNA of 310–1500 bp entered the nuclei of digitonin treated cells in the absence of cytosolic extract by an active transport process. Both the size limit and the intensity of DNA nuclear transport could be increased by the attachment of strong nuclear localization signals. Conjugation of a 900 bp expression cassette to nuclear localization signals increased both its nuclear entry and expression in microinjected, living cells.

Goblet cell membrane differentiations in the midgut of a lepidopteran larva

1976 ◽  
Vol 20 (2) ◽  
pp. 357-375
Author(s):  
N.E. Flower ◽  
B.K. Filshie
Keyword(s):  
Plasma Membrane ◽  
Cell Membrane ◽  
Active Transport ◽  
Goblet Cell ◽  
Goblet Cells ◽  
Wide Channel ◽  
Lepidopteran Larvae ◽  
Lanthanum Tracer ◽  
Cell Cavity

So-called goblet cells are present in the midgut of lepidopteran larvae. They are thought to be involved in the active transport of potassium out of the haemolymph and into the gut lumen. A number of plasma membrane differentiations within the goblet cell cavity has been investigated using conventional staining, lanthanum tracer and freeze-etch techniques. Of particular interest are junction-like inter- and intra-membrane differentiations found on the villus-like cytoplasmic projections present at the apical tip of the goblet cell cavities. These cytoplasmic projections appear to act as a valve; in some cases they seem to close off the top of the goblet cell cavity, so isolating it from the gut lumen, while in other cases they are spread apart leaving a wide channel from the cavity into the lumen. The junction-like structures on these cytoplasmic projections are different in structure from the septate-type junctions which seal the midgut cells together at their apical borders, and the 2 types are present on the same plasma membrane, often within one micron of each other. The need for a different type of junction may possibly be related to the fact that it occurs between 2 areas of the same plasma membrane. The morphology of this unusual junction-like structure is discussed and 2 diagrams are presented to illustrate our interpretation of its structure.

Steps in p-aminohippurate transport by kidney slices

1958 ◽  
Vol 196 (1) ◽  
pp. 86-92 ◽  
Author(s):  
Ernest C. Foulkes ◽  
Benjamin F. Miller
Keyword(s):  
Cell Membrane ◽  
Transport System ◽  
Rate Constants ◽  
Extracellular Space ◽  
Concentration Ratio ◽  
Tissue Concentration ◽  
The Other ◽  
Facilitated Diffusion ◽  
Tubular Lumen ◽  
Cortical Slices

The existence of two intracellular fractions of PAH was demonstrated in renal cortical slices of the rabbit on incubation with C14-labeled PAH. One of these fractions is rapidly diffusible and rapidly equilibrates with extracellular PAH. The other fraction, in contrast, diffuses and equilibrates slowly; it is responsible for the high slice to medium concentration ratio of PAH. On the basis of these results a model of the PAH transport system in slices is proposed. This consists of step I, the diffusion of PAH from the medium into the extracellular space in the tissue; there follows step II, a facilitated diffusion step at the peritubular cell membrane; within the cell step III builds up a high tissue concentration of PAH; finally step IV transfers PAH across the luminal border of the cell into the tubular lumen from which it may diffuse back into the medium. Experiments were designed in which each of these steps could be measured individually and their rate constants determined. Alteration of the value of these rate constants by specific drugs localizes the action of such compounds at the peritubular cell membrane (Benemid, 9-alphafluorohydrocortisone) or at the level of both steps II and III in the case of DNP, octanoate and Diodrast. An explanation is also offered for the effect of cold on PAH influx and efflux. It can be calculated that the contribution of step IV to the turnover of PAH in slices is not quantitatively significant.

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