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Medication: Nanoparticles for Imaging and Drug Delivery
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
The tight epithelial barrier surrounding the central nervous system is highly lipophilic. Small lipophilic molecules can cross by dissolving through the lipid bilayer (for instance, alcohol, caffeine, nicotine, and antidepres-sants). Other molecules needed for the brain to function make use of specific natural transport mechanisms in the cell membranes. Small polar molecules, such as glucose and amino acids, and larger proteins, like insulin and the iron-transporting protein transferrin, are transported through the blood brain chemical traffic by “gatekeeping” processes. Each of the required small molecules has its own transporter protein that carries it through the cell membranes—this process is called carrier-mediated transport. For proteins, specific cell membrane receptors bind the large molecules and pull them across the barrier in a mechanism called receptor-mediated transcytosis. In addition, some ionic proteins (e.g., cationic albumin) bind to and penetrate the blood-brain barrier using electrostatic interactions, in a process called absorptive-mediated transcytosis [344-346].
Physiological basis and concepts of electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
The membrane proteins (cf. Figure 2.1) play a significant part in the exchange processes between the two compartments. At the functional level, a distinction can be made between two groups of proteins, transport proteins, and receptor proteins. Transport proteins allow substances to travel across the membrane from one compartment to the other. They are generally characterized by high specificity, i.e. each transport protein enables the transportation of only one or a small number of specific substances. Transport proteins are termed carrier molecules, membrane pumps, or membrane channels according to their particular characteristic. By contrast, receptor proteins combine specifically with certain molecules (e.g. hormones) and serve in the transfer of information across the membrane.
Physical properties of the body fluids and the cell membrane
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
The transport of essential water-soluble molecules across the cell membrane is achieved through the use of special transmembrane proteins that have a high specificity for a certain type or class of molecules. These membrane transport proteins come in two basic types: carrier proteins and channel proteins. The carrier proteins bind to the solute and then undergo a change in shape or conformation (ding to dong; see Figure 3.7), which allows the solute to traverse the cell membrane. The carrier protein, therefore, changes between two shapes, alternately presenting the solute-binding site to either side of the membrane. Channel proteins actually form water-filled pores that penetrate across the cell membrane. Solutes that cross the cell membrane by either carrier or channel proteins are said to be passively transported.
Structure and diversity of bacterial communities in the water column of three reservoirs in Yun-Gui Plateau, China
Published in Inland Waters, 2023
The gene functions in these reservoirs suggested that the bacterial community is involved in various biogeochemical processes, including carbohydrate, energy, and lipid metabolisms. The dominant abundance of the ‘environmental information processing’ category may indicate the presence of different types of compounds in the water, such as organic nutrients, heavy metals, or other pollutants. Some of these compounds would be uptaken by cells, which requires membrane transport (belongs to environmental information processing). Membrane transport proteins play an essential role in efficient metabolism and the translocation of solutes, such as nutrients, ions, drugs, and endogenous bioactive substances (Piepenbreier et al. 2017). Moreover, metabolism dominance proved the numerous activities bacteria involved in various pathways concerning metabolism. These results highlighted the gene diversity of bacteria and the multi-facet roles played by bacteria in such plateau reservoirs. To some extent, the increasing nutrient contents could increase the bacterial diversity, which implies the eutrophic status of these reservoirs.
Progress in spray-drying of protein pharmaceuticals: Literature analysis of trends in formulation and process attributes
Published in Drying Technology, 2021
Joana T. Pinto, Eva Faulhammer, Johanna Dieplinger, Michael Dekner, Christian Makert, Marco Nieder, Amrit Paudel
Transport proteins carry gases, sugars, amino acids, lipids, synthetic drugs, etc., through the vascular system and tissue. Two well-known families of transport proteins are globins and serum albumins.[95] Hemoglobin is the transporter of oxygen.[96] Our literature research found that oxyhemoglobin was one of the first proteins to be successfully spray-dried within a pharmaceutical context.[97] Also spray-drying studies of myoglobin are reported, given its ease of availability and low cost.[47,98] Serum albumins are the most abundant proteins in plasma and they maintain the osmotic pressure in blood, the acid-base balance in plasma, and transport various compounds.[95] Due to its low cost and availability, bovine serum albumin (BSA) has been extensively used as a model protein for spray-drying.[24,98–115] β-lactoglobulin, another protein form bovine source, has also been employed as model.[110]