Table transmembrane

Verapamil. Verapamil hydrochloride (see Table 1) is a synthetic papaverine [58-74-2] C2qH2 N04, derivative that was originally studied as a smooth muscle relaxant. It was later found to have properties of a new class of dmgs that inhibited transmembrane calcium movements. It is a (+),(—) racemic mixture. The (+)-isomer has local anesthetic properties and may exert effects on the fast sodium channel and slow phase 0 depolarization of the action potential. The (—)-isomer affects the slow calcium channel. Verapamil is an effective antiarrhythmic agent for supraventricular AV nodal reentrant arrhythmias (V1-2) and for controlling the ventricular response to atrial fibrillation (1,2,71—73). 

Verapamil (Table 1), the first slow channel calcium blocker synthesized to selectively inhibit the transmembrane influx of calcium ions into cells, lowers blood pressure in hypertensive patients having good organ perfusion particularly with increased renal blood flow. Sustained-release verapamil for once a day dosing is available for the treatment of hypertension. Constipation is a prominent side effect. Headache, dizziness, and edema are frequent and verapamil can sometimes cause AV conduction disturbances and AV block. Verapamil should not be used in combination with -adrenoceptor blockers because of the synergistic negative effects on heart rate and contractile force. 

Table 12.2 Amino acid sequences of the transmembrane helices of the photosynthetic reaction center in Rhodobacter sphaeroides...

Thus, Og and cytochrome c oxidase are the final destination for the electrons derived from the oxidation of food materials. In concert with this process, cytochrome c oxidase also drives transport of protons across the inner mitochondrial membrane. These important functions are carried out by a transmembrane protein complex consisting of more than 10 subunits (Table 21.2). 

ATP synthase actually consists of two principal complexes. The spheres observed in electron micrographs make up the Fj unit, which catalyzes ATP synthesis. These Fj spheres are attached to an integral membrane protein aggregate called the Fq unit. Fj consists of five polypeptide chains named a, j3, y, 8, and e, with a subunit stoichiometry ajjSaySe (Table 21.3). Fq consists of three hydrophobic subunits denoted by a, b, and c, with an apparent stoichiometry of ajbgCg.ig- Fq forms the transmembrane pore or channel through which protons move to drive ATP synthesis. The a, j3, y, 8, and e subunits of Fj contain 510, 482, 272, 146, and 50 amino acids, respectively, with a total molecular mass... 

The four mammalian ARs are members of the rhodopsin-like Class A family of GPCRs, which contain seven transmembrane helical domains ( TMs). Character istics of the four subtypes of the human ARs, length of their primary sequences, their chromosomal localization, and their signaling pathways are given in Table 1. The A2a receptor is considerably longer than the other three subtypes, due to its extended carboxy-terminal. 

It is possible to calculate whether a particular sequence of amino acids present in a protein is consistent with a transmembrane location. This can be done by consulting a table that hsts the hydrophobicities of each of the 20 common amino acids and the free energy val-... 

There is good agreement that the two high-affinity Ca sites are within = 10 A of each other (Table II) [132,390,404-409], Their localization within the bilayer is supported by the observation [130,131] that site-specific mutagenesis of several amino acids within the putative transmembrane helices interferes with Ca binding and with the Ca -dependent phosphorylation of the enzyme by ATP, but has no effect on the Ca -independent phosphorylation by inorganic phosphate. 

Fromm and Spanswick [79] found that electrical stimulation of a plant is followed by ion shifts which are most striking in the phloem cells. While their content of potassium and chloride was diminished after stimulation, the amount of cytoplasmic calcium increased slightly (Table 1). These displacements lead to the conclusion that Ca + influx as well as and CP efflux are involved in the propagation of action potentials. The main difference between propagation of action potentials in animals and plants is that in an axon there is the K /Na transmembrane transport but in phloem cells the K /Ca channels are involved in this process [Fig. 22(b)]. 

The 4TM receptors are pentameric complexes composed of subunits of 420 to 550 amino acids. The subunits exhibit sequence identities from 25 to 75%, with a similar distribution of hydrophobic and hydrophilic domains (Table 3.1). The hydrophilic 210 to 230 amino-acid N-terminal domain is followed by three closely spaced hydrophobic and putative transmembrane domains, then a variable-length intracellular loop, and finally a fourth putative transmembrane region shortly before the C-terminus (Figure 3.1). Of the four candidate transmembrane regions, evidence suggests that TM2 forms an a-helix, while the other hydrophobic regions more likely are folded as (3-sheets. 

Extracellular ATP has been demonstrated to activate a depolarizing current in different neuronal and non-neuronal cell types. These receptors are also referred to as P2 receptors. The receptors can further be divided into the G-protein-coupled P2Y receptors and the ligand-gated ion channels P2X. Currently, seven P2X receptors (P2XJ-P2X- ) have been cloned (Table 3.3). The receptors exhibit between 26 and 50% overall amino-acid identities, with the highest level of conservation in the extracellular and transmembrane regions. P2X7 (also called P2Z) is the most distant member of the family. 

The 5-HTy receptor is part of the G-protein superfamily of receptors, which contains seven transmembrane regions, and its stimulation leads to an increase in cAMP production (Thomas Hagan, 2004). The 5-HT7 receptor is expressed in a number of telencephalic, diencephalic, mesencephalic, and rhombencephalic areas (Table 9.8). 

TABLE 2 Estimated fluctuation changes in the transmembrane and cytoplasmic a-helices for a variety of membrane proteins and their complexes (Hz)°... 

The IFN-y receptor (the type II receptor) displays a more limited cellular distribution than that of the type I receptors (Table 8.5). This receptor is a transmembrane glycoprotein of molecular mass 50 kDa, which appears to function as a homodimer. The extracellular IFN-y binding region consists of approximately 200 amino acid residues folded into two homologous domains. Initiation of signal transduction also requires the presence of a second transmembrane glycoprotein known as AF-1 (accessory factor 1), which associates with the extracellular region of the receptor. 

Two allelic trembler mutations, which affect only the PNS, result from different point mutations in transmembrane domains of peripheral myelin protein-22 (PMP-22) [1,45] (Table 4-2). The trembler phenotypes are characterized by hypomyelination, continued Schwann cell proliferation and partial paralysis of the limbs. These murine mutants are animal models for some of the inherited human neuropathies caused by abnormalities of the... 

---