Membranes gated pores

It functions by generating a gated pore in the membrane to permit passage of glucose the pore is conformationally dependent on the presence of glucose and can oscillate rapidly (about 900 times/s). 

Internalization The toxins diffuse laterally in the membrane, bind to protein receptors and are internalized by receptor-mediated endocyto-sis. After this stage is completed, the toxins are protected against antibody inactivation. The internalized HC forms aggregates and induces pores in endosomal membrane. The pores serve as gates through which the LC enters a cytoplasm (Ledoux et al., 1994). 

Anions of lipid-soluble phenols such as 2,4-dini-trophenol can serve as effective carriers of protons (Chapter 18). However, proteins usually serve as the natural carriers, both of protons and of other ions. A protein is sometimes pictured as rotating to present the solute-binding surface first to one side, then to the other side of a membrane. However, gated pores or channels are probable for most biological transport. 

Ion channels are transmembrane proteins that span the cell membrane and are formed from one or more protein subunits. The channels are shaped like tunnels, which form pores through the plasma membrane. The pores have gates that open and close to allow ions to diffuse down their chemical gradient and move in or out of a cell. Ion channels are specific for certain types (and combinations of types) of ions, such as chloride, sodium, potassium, and calcium. 

Fig. 4 Ion channel biosensor. The ion channels and their surrounding lipid bilayer are accommodated in a microstructured polymer membrane. Gating of the ion channel by an analyte results in an influx of ions into the pore. The concentration change is detected by surface plasmons, which are excited by light in the underlying metal layer...

Figure 4.4 Ion channels, proteins on the cell membrane, act as gates that allow ions, such as sodium and potassium, through the plasma membrane. The pores open and close to regulate the movement of ions and, thus, the communication between neurons.

On the other hand, in the m state, the exposure of some lysines change as would be expected for a gated pore carrier. Thus, lysine 42 switches from the cytosolic side to the matrix side. Lysines 91, 93 and 95 appear on the cytosoUc face, and 106 disappears. Lysine 146 is exposed only on the matrix side and 162 appears from the cytosolic side. A rather unsatisfactory aspect of the model is the necessity for the hydrophilic segment 230-259 to cross the membrane. This appears necessary if hydrophobic segment V spans the membrane, 198 and 205 are cytosolic, and 259, 262 and 267 are also cytosohc. Since these last lysines are very weakly reactive it is possible they are deep in a pocket, not shown in the model. 

Connexin protein is unique in forming a gated pore through two membranes. Two questions particular to this structure are (1) how is the junctional channel assembled (e.g., how do the two hemichannels find each other and interact to form a stable structure) and (2) what is the interaction between... 

The Na, K -ATPase spans the plasma membrane, much like a gated pore, with a binding site for 3 Na ions open to the intracellular side (Fig. 10.12). Energy from... 

Voltage-gated Ca2+ channels are Ca2+-selective pores in the plasma membrane of electrically excitable cells, such as neurons, muscle cells, (neuro) endocrine cells, and sensory cells. They open in response to membrane depolarization (e.g., an action potential) and permit the influx of Ca2+ along its electrochemical gradient into the cytoplasm. 

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