Integral proteins of membrane

Fungal chitin synthases are found as integral proteins of the plasma membrane and in chitosomes a divalent cation, Mg(II), is necessary for enzyme activity but neither primers nor a hpid intermediate are required. The substrate and free GlcNAc activate the allosteric enzyme. UDP, the byproduct of the enzymatic activity, is strongly inhibitory to chitin synthase however, it may be metabohzed readily to UMP by a diphosphatase. 

The Major Integral Proteins of the Red Blood Cell Membrane Are the Anion Exchange Protein the Glycophorins... 

Figure 52-4. Diagrammatic representation of the interaction of cytoskeletal proteins with each other and with certain integral proteins of the membrane of the red blood cell. (Reproduced, with permission, from Beck WS, Tepper Rl Hemolytic anemias III membrane disorders. In Hematology, 5th ed. Beck WS [editor]. The MIT Press, 1991.)...

Singer, S. (1990). The structure and insertion of integral proteins in membranes. Annu. Rev. Cell Biol. 6, 247-296. 

Adenylyl cyclase (Fig. 12-13) is an integral protein of the plasma membrane, with its active site on the cytosolic face. It catalyzes the synthesis of cAMP from ATP ... 

The heme cofactors of a and b cytochromes are tightly, but not covalently, bound to their associated proteins the hemes of c-type cytochromes are covalently attached through Cys residues (Fig. 19-3). As with the flavoproteins, the standard reduction potential of the heme iron atom of a cytochrome depends on its interaction with protein side chains and is therefore different for each cytochrome. The cytochromes of type a and b and some of type c are integral proteins of the inner mitochondrial membrane. One striking exception is the cytochrome c of mitochondria, a soluble protein that associates through electrostatic interactions with the outer surface of the inner membrane. We encountered cytochrome c in earlier discussions of protein structure (see Fig. 4-18). 

One of the major integral proteins of the erythrocyte membrane is the anion channel, or band-3 protein, which moves Cl- and HC03 anions across the membrane. The anion transporter has two identical subunits with molecular weights of about 95,000, and each subunit probably has 10 or 11 transmembrane helices. The band-3 protein is attached to the spectrin cytoskeleton through a smaller protein, anky-rin. The cytosolic domain of the anion transporter also binds the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. 

The light-sensitive protein complex in the rods, rho-dopsin, consists of 1 l-c/s-retinal bound as a Schiff s base to a protein, opsin. Rhodopsin is an integral constituent of membranes that form a stack of disks at one end of the cell. Cone cells, which are responsible for the perception of color, contain similar complexes in infoldings of the plasma membrane. 

Johansson I, Larsson C, Ek B, Kjellbom P. 1996. The major integral proteins of spinach leaf plasma membranes are putative aquaporins and are phosphorylated in response to Ca2+ and apoplastic water potential. Plant Cell 8 1181-1191. 

Several BA biosynthetic enzymes also occur in subcellular locations other than the cytosol. Of the five non-cytosolic enzymes involved in the conversion of (5)-reticuline to dihydrosanguinarine, four - BBE, CFS, SPS, and MSH - were localized to a membrane fraction with a unique density (8 = 1.14 g mL 1),25 26,29 38 while one (PPH) was associated with a membrane fraction of the same density as the ER (8 = 1.11 g mL 1).155 STS, which is involved in morphine biosynthesis, was also localized to a microsomal fraction with a density (8 = 1.14 g mL 1) higher than expected for the ER.40 With the exception of BBE, all of these non-cytosolic enzymes are P450-dependent and, as such, must be integral proteins of the ER, or ER-derived compartments.110... 

Roosild TP, Greenwald J, Vega M, Castronovo S, Riek R, Choe S. NMR structure of Mistic, a membrane-integrating protein for membrane protein expression. Science 2005 307 1317-1321. Oxenoid K, Chou JJ. The structure of phospholamban pentamer reveals a channel-like architecture in membranes. Proc. Natl. Acad. Sci. U.S.A. 2005 102 10870-10875. 

This reaction is the only dehydrogenation reaction of the TCA cycle in which NAD+ does not mediate the transport of reducing equivalents. The FAD is covalently linked to a histidyl residue of the enzyme, which is an integral protein of the inner mitochondrial membrane and contains iron-sulfur centers that undergo redox changes Fe " "). Reducing equivalents from FADH2... 

FIGURE 5-11 Diagram of how various ciasses of proteins associate with the iipid biiayer. Integral (transmembrane) proteins span the bIlayer. LIpId-anchored proteins are tethered to one leaflet by a long covalently attached hydrocarbon chain. Peripheral proteins associate with the membrane primarily by specific noncovalent Interactions with Integral proteins or membrane lipids. 

Soluble proteins exhibit hundreds of distinct localized folded structures, or motifs (see Figure 3-6). In comparison, the repertoire of folded structures in Integral membrane proteins Is quite limited, with the hydrophobic a helix predominating. Integral proteins containing membrane-spanning ct-hellcal domains are embedded in membranes by hydrophobic Interactions with specific lipids and probably also by Ionic Interactions with the polar head groups of the phospholipids. 

Here, all the integral proteins of the erythrocyte membrane are solubilized by a nonionic detergent, such as octylglucoside. The glucose uniporter GLUT1 can be purified by chromatography on a column containing a specific monoclonal antibody and then incorporated into liposomes made of pure phospholipids. 

Knopfel M, Schulthess G, Funk F and Hausee H (2000) Characterization of an integral protein of the brush border membrane mediating the transport of divalent metal ions. Biophys J 79 874-884. 

Step 6. Formation of Fumarate—FAD-Linked Oxidation Succinate is oxidized to fumarate, a reaction that is catalyzed by the enzyme succinate dehydrogenase. This enzyme is an integral protein of the inner mitochondrial membrane. We shall have much more to say about the enzymes bound to the inner mitochondrial membrane in Ghapter 20. The other individual enzymes of the citric acid cycle are in the mitochondrial matrix. The electron acceptor, which is FAD rather than NADA is covalently bonded to the enzyme succinate dehydrogenase is also called a flavoprotein because of the presence of FAD with its flavin moiety. In the succinate dehydrogenase reaction, FAD is reduced to FADHo and succinate is oxidized to fumarate. 

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