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Cell Biology for Bioprocessing
Published in Wei-Shou Hu, Cell Culture Bioprocess Engineering, 2020
Uniporters transfer a single solute from a high concentration side to a low concentration side, e.g., the GLUT1 transporter for glucose and the GLUT5 transporter for fructose. Symporters and antiporters transfer two solutes simultaneously. A transporter that delivers the two solutes in the same direction is called symporter. Conversely, an antiporter transfers two solutes in opposite directions.
The Cell Membrane in the Steady State
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
A cotransporter is a transmembrane protein that couples the transport of substances, against electrochemical potential gradients, to the transport of other substances down electrochemical potential gradients, again without directly involving ATP hydrolysis. If the substances are moved in the same direction, the cotransporter is a symporter. If the substances are moved in opposite directions, the cotransporter is an antiporter. If the substances moved by an antiporter are ions, the antiporter is an ion exchanger. An example of a symporter is the K+-Cl– symporter that moves one K+ and one Cl– outward. K+ are moved down their electrochemical potential gradient, which provides the energy for driving Cl– outward and establishing an electrochemical potential gradient for Cl– that can drive them passively inward. This electrochemical potential gradient is essential for the action of some inhibitory synapses (Section 6.2.2). Note that the driving electrochemical potential of K+ is established in the first place by active transport that utilizes ATP hydrolysis. The K+-Cl– symporter is also known as a KCC2 (potassium chloride cotransporter 2). In some cases, a Na+-K+-2Cl– symporter (also known as NKCC) transports Cl– ions inward from the extracellular medium and establishes an electrochemical potential gradient for Cl– that can drive them passively outward, as in presynaptic inhibition (Section 6.4). The energy for driving the NKCC symporter is the electrochemical potential for Na+, which again is established by active transport that utilizes ATP hydrolysis. Because of this, the action of cotransporters is often referred to as secondary active transport. Both the K+-Cl– and the Na+-K+-2Cl– symporters are electrically neutral, as no net transfer of charge occurs, because equal quantities of positive charge and negative charge are moved in the same direction.
X-Nuclei MRI and Energy Metabolism
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Active transport. Active transport is defined as the movement of a solute across a membrane from the side of low electrochemical potential to the side with high electrochemical potential. The solute moves against its electrochemical gradient, which requires an outside source of energy. Active transport can be classified in two main categories: Primary active transport: This kind of transport needs ATP hydrolysis as a source of energy to transport ions or other solutes against their electrochemical gradient. Different types of proteins or enzymes (called ATPases) are responsible for primary active transport: P-type ATPase: Na+/K+-ATPase (sodium potassium pump), Ca2+-ATPase (calcium pump), H+-ATP (proton pump)F-ATPase: Mitochondrial ATPase, chloroplast ATPaseV-ATPase: Vacuolar ATPaseABC (ATP binding cassette) transporter: MDR, CFTR, etc.Secondary active transport: The electrochemical gradients set up by primary active transport store energy, which can be released as some ions move back down their gradients by facilitated diffusion. Secondary active transport uses this energy stored in these gradients to move other substances against their own gradients. The movement of some solutes down their electrochemical gradient across the membrane by facilitated diffusion is thus coupled with the active transport of other solutes against their electrochemical gradient. Two types of integral membrane proteins called cotransporters are responsible for secondary active transport: Symporters: A symporter allows two or more different kinds of solutes to cross the membrane in the same direction. Examples of symporters are: Na+/K+/2Cl–- symporter (NKCC), which uses the Na+ electrochemical gradient to import one K+ and 2 Cl– inside the cell; Na+/glucose cotransporter (SGLT); Cl–/K+ symporter; Na+/HCO3 cotransporter.Antiporters, or exchangers: An antiport or exchanger allows two or more different kinds of solutes to cross the membrane in one direction while others go in the other direction. Examples of exchangers are Na+/Ca2+ exchanger (which is reversible); Na+/H+ antiporter; Cl-/HCO-3 exchanger.
Treatment and high value utilization of glutamic acid wastewater
Published in Preparative Biochemistry & Biotechnology, 2022
Fupeng Yu, Chen Zhao, Le Su, Song Zhang, Xin Sun, Kunlun Li, Qiulin Yue, Lin Zhao
The whole genome of Bacillus licheniformis M 2020051 was sequenced. The whole-genome size was 4,311,767 bp, the GC content percentage was 45.87%, and there were 4480 coding genes, including three kinds of rRNA (5S rRNA, 16S rRNA, 23S rRNA) and 66 tRNA genes. The nhaC gene and the mrp gene were detected from whole-genome sequencing, both of which encode the Na+/H+ antiporter. Na+/H+ antiporter, also known as Na+/H+ pump, is a type of transmembrane protein responsible for ion exchange, and plays a key role in maintaining the normal salt concentration and pH steady state of cells. Among them, mrp is a common gene encoding an antiporter, which is a hetero-oligomeric complex composed of seven subunits. Each subunit is indispensable for the activity of the protein. It exists in high concentrations of Na+ and K+ under the circumstances, the mrp system is essential to maintain the bacterial ion balance and acid-base homeostasis. At the same time, the proH gene was detected, which was related to the synthesis of proline. Proline is a kind of osmotic pressure protection substance, which can relieve the pressure of high salt. This explained why Bacillus licheniformis was resistant to high salt and hypertonicity. At the same time, it was detected that the bacterium contained four genes such as capA, capB, capC, capE and glt gene cluster, which are necessary for the synthesis of polyglutamic acid. It was proved that the polyglutamic acid synthesized by this bacterium is bound to the cell wall and belongs to the binding type.[3,24]