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RIBOSE 5-PHOSPHATE FROM THE OXIDATIVE ARM OF H O THE PATHWAY C To generate ribose 5-phosphate from the oxidative pathway generic cialis super active 20mg visa, the ribulose 5-phos- H phate formed from the action of the two oxidative steps is isomerized to produce HO ribose 5-phosphate (a ketose-to-aldose conversion discount cialis super active 20mg with visa, similar to fructose 6-phos- phate being isomerized to glucose 6-phosphate 20mg cialis super active with visa; see section III purchase 20mg cialis super active with amex. The H C OH ribose 5-phosphate can then enter the pathway for nucleotide synthesis 20mg cialis super active, if needed, H or can be converted to glycolytic intermediates, as described below for the nonox- CH OPO2– 2 3 idative phase of the pentose phosphate pathway. The pathway through which the Glucose 6–phosphate ribose 5-phosphate travels is determined by the needs of the cell at the time of its synthesis. The Nonoxidative Phase of the Pentose dehydrogenase NADPH + H+ Phosphate Pathway The nonoxidative reactions of this pathway are reversible reactions that allow inter- O mediates of glycolysis (specifically glyceraldehyde-3-P and fructose-6-P) to be C converted to five-carbon sugars (such as ribose-5-P), and vice versa. The needs of H the cell will determine in which direction this pathway proceeds. If the cell has pro- O HO duced ribose-5-P, but does not need to synthesize nucleotides, then the ribose-5-P will be converted to glycolytic intermediates. If the cell still requires NADPH, the H C OH ribose-5-P will be converted back into glucose-6-P using nonoxidative reactions H C (see below). And finally, if the cell already has a high level of NADPH, but needs 2– CH2OPO3 to produce nucleotides, the oxidative reactions of the pentose phosphate pathway will be inhibited, and the glycolytic intermediates fructose-6-P and glyceraldehyde- 6–Phosphoglucono– δ–lactone 3-P will be used to produce the five carbon sugars using exclusively the nonoxida- tive phase of the pentose phosphate pathway. THE CONVERSION OF RIBOSE 5-PHOSPHATE TO H+ GLYCOLYTIC INTERMEDIATES The nonoxidative portion of the pentose phosphate pathway consists of a series O O– of rearrangement and transfer reactions that first convert ribulose 5-phosphate to C ribose 5-phosphate and xylulose 5-phosphate, and then the ribose 5-phosphate H and xyulose 5-phosphate are converted to intermediates of the glycolytic path- HO way. The enzymes involved are an epimerase, an isomerase, transketolase, and transaldolase. H C OH The epimerase and isomerase convert ribulose 5-phosphate to two other 5-carbon H C OH sugars (Fig. The isomerase converts ribulose 5-phosphate to ribose 5-phos- CH OPO2– 2 3 phate. The epimerase changes the stereochemical position of one hydroxyl group (at 6–Phosphogluconate carbon 3), converting ribulose 5-phosphate to xylulose 5-phosphate. Transketolase transfers 2-carbon fragments of keto sugars (sugars with a keto NADP+ group at C2) to other sugars. Transketolase picks up a 2-carbon fragment from xylu- 6–phosphogluconate + dehydrogenase NADPH + H lose 5-phosphate by cleaving the carbon–carbon bond between the keto group and CO2 the adjacent carbon, thereby releasing glyceraldehyde 3-phosphate (Fig. The 2-carbon fragment is covalently bound to thiamine pyrophosphate, which transfers CH2OH C Xyulose 5-phosphate has recently been identified as an activator of protein phos- H phatase 2A (PP2A). PP2A removes phosphates from PFK-2 and from a transcription H C OH factor that binds to carbohydrate response elements in promoters of genes such as CH OPO2– pyruvate kinase. The hydrolysis of the phosphates activates both proteins, such that xyulose 2 3 5-phosphate can regulate pathways relating to both carbohydrate and fat metabolism. Carbon 1 of glucose 6-phosphate is oxidized to an acid and then released as CO2 in an oxidative decarboxylation reaction. The red blood cell is dependent on this enzyme for a source of NADPH to maintain reduced levels of glutathione, one of its major defenses against oxidative stress (see Chapter 24). Glucose 6-phosphate dehydrogenase defi- ciency is the most common known enzymopathy, and affects approximately 7% of the world’s population and about 2% of the U. Most glucose 6-phosphate dehydrogenase–deficient individuals are asymptomatic but can undergo an episode of hemolytic anemia if exposed to certain drugs, to certain types of infections, or if they ingest fava beans. When questioned, Al Martini replied that he did not know what a fava bean was and had no idea whether he was sensitive to them. CH2OH C it to the aldehyde carbon of another sugar, forming a new ketose. The role of thiamine-pyrophosphate here is thus very similar to its role in the oxidative decar- HO boxylation of pyruvate and -ketoglutarate (see Chapter 20, section I. Two H C OH reactions in the pentose phosphate pathway use transketolase; in the first, the 2-car- CH OPO2– 2 3 bon keto fragment from xylulose 5-phosphate is transferred to ribose 5-phosphate Xylulose 5–phosphate to form sedoheptulose 7-phosphate, and in the other, a 2-carbon keto fragment (usu- + ally derived from xyulose 5-phosphate) is transferred to erythrose 4-phosphate to H O form fructose 6-phosphate. C H H C OH H O H C CH OPO2– 2 3 H Ribose 5–phosphate H C OH thiamine H pyrophosphate transketolase CH OPO2– 2 3 H O Ribose 5–phosphate C isomerase H CH OPO2– 2 3 CH2OH Glyceraldehyde 3–phosphate + H CH2OH H C OH C CH OPO2– 2 3 HO Ribulose 5–phosphate H epimerase H H CH2OH CH OPO2– 2 3 Sedoheptulose 7–phosphate HO H C OH Fig. Two-carbon unit transferred by trans- CH OPO2– ketolase. Transketolase cleaves the bond next to 2 3 the keto group and transfers the 2-carbon keto Xylulose 5–phosphate fragment to an aldehyde. Thiamine pyrophos- phate carries the 2-carbon fragment, forming a Fig. Ribulose 5-phosphate is epimerized (to xyulose 5-phosphate) and isomerized (to covalent bond with the carbon of the keto group. CHAPTER 29 / PATHWAYS OF SUGAR METABOLISM: PENTOSE PHOSPHATE PATHWAY, FRUCTOSE, AND GALACTOSE METABOLISM 535 Transaldolase transfers a 3-carbon keto fragment from sedoheptulose 7-phos- The transketolase activity of red phate to glyceraldehyde 3-phosphate to form erythrose 4-phosphate and fructose 6- blood cells is used to measure thi- phosphate (Fig. The aldol cleavage occurs between the two hydroxyl carbons amine nutritional status and diag- nose the presence of thiamine deficiency.

Neurologic Control of the Musculoskeletal System 147 64 buy cheap cialis super active 20mg line. Cerebellar stimulation for spastic cerebral palsy: preliminary report generic 20mg cialis super active fast delivery; on-going double blind study purchase 20mg cialis super active fast delivery. Experience with 509 plate electrodes implanted epidurally from C1 to L1 cialis super active 20 mg on-line. Hugenholtz H generic 20mg cialis super active amex, Humphreys P, McIntyre WM, Spasoff RA, Steel K. Cer- vical spinal cord stimulation for spasticity in cerebral palsy. Padovani R, Tognetti F, Pozzati E, Servadei F, Laghi D, Gaist G. The treatment of spasticity by means of dorsal longitudinal myelotomy and lozenge-shaped griseotomy. Role of nerve blocks in the foot and ankle in cerebral palsy: therapeutic and diagnostic. Traditional pharmaco- logical treatments for spasticity. Intramuscular alcohol as an aid in management of spastic cerebral palsy. Treatment of spasticity in injection of dilute alcohol at the motor point or by epidural route. Clin- ical extension of an experiment on the decerebrate cat. Intramuscular neurolysis for spasticity in children. General anesthesia use in phenol intramuscu- lar neurolysis in young children with spasticity. Insufficiency of the hip adductor after an- terior obturator neurectomy in 42 children with cerebral palsy. Hip adductor transfer compared with adductor teno- tomy in cerebral palsy. Intrapelvic ob- turator neurectomy in cerebral palsy. Management of in- trinsic spasticity in the hand with phenol injection or neurectomy of the motor branch of the ulnar nerve. Doute DA, Sponseller PD, Tolo VT, Atkins E, Silberstein CE. Soleus neurectomy for dynamic ankle equinus in children with cerebral palsy. Medical treatment for spasticity in children with cerebral palsy. Dantrolene sodium: a review of its pharmacological properties and therapeutic efficacy in spasticity. Dantrolene sodium suspension in treatment of spastic cerebral palsy. Botulinum toxin: historical perspective and poten- tial new indications. Botulinum toxin: chemistry, pharmacology, toxicity, and im- munology. Dosing, administration, and a treatment algorithm for use of botulinum toxin A for adult-onset spasticity. Histologic assessment of dose-related diffusion and muscle fiber response after therapeutic bot- ulinum A toxin injections. Analgesic effects of botulinum toxin A: a randomized, placebo-controlled clinical trial. Use of botulinum toxin type F injections to treat torticollis in patients with immunity to botulinum toxin type A. Koman LA, Mooney JF III, Smith B, Goodman A, Mulvaney T. Man- agement of cerebral palsy with botulinum-A toxin: preliminary inves- tigation. An evaluation of botulinum- A toxin injections to improve upper extremity function in children with hemiplegic cerebral palsy [see comments]. Recommendations for the use of botulinum toxin type A in the management of cerebral palsy.

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ACRP30/adiponectin: an adipokine regulating glucose and lipid metabolism proven cialis super active 20 mg. Trends in Endocrinology and Metabolism 2002 order cialis super active 20 mg with mastercard;13:84–89 discount cialis super active 20mg with visa. The response to long-term overfeeding in identical twins buy cheap cialis super active 20 mg line. Girard J generic 20 mg cialis super active with amex, Perderbeau D, Foufelle F, Prip-Buus C, Ferre P. Regulation of lipogenic enzyme gene expres- sion by nutrients and hormones. The effects of weight loss on the activity and expression of adi- pose-tissue lipoprotein lipase in very obese humans. The body-mass index of twins who have been reared apart. Which of the following is involved in the synthesis of triacylgycerols in adipose tissue? A molecule of palmitic acid, attached to carbon 1 of the glycerol moiety of a triacylglycerol, is ingested and digested. It passes into the blood, is stored in a fat cell, and ultimately is oxidized to carbon dioxide and water in a muscle cell. Choose the molec- ular complex in the blood in which the palmitate residue is carried from the lumen of the gut to the surface of the gut epithe- lial cell. A patient with hyperlipoproteinemia would be most likely to benefit from a low-carbohydrate diet if the lipoproteins that are elevated in blood are which of the following? Which of the following is a characteristic of sphingosine? Newly synthesized fatty acids are not immediately degraded because of which of the following? Cholesterol, which is transported in the blood in lipoproteins because of its absolute insolubility in water, serves as a stabilizing component of cell membranes and as a precursor of the bile salts and steroid hormones. Precursors of cholesterol are converted to ubiquinone, dolichol, and, in the skin, to cholecalciferol, the active form of vita- min D. As a major component of blood lipoproteins, cholesterol can appear in its free, unesterified form in the outer shell of these macromolecules and as cho- lesterol esters in the lipoprotein core. Cholesterol is obtained from the diet or synthesized by a pathway that occurs in most cells of the body, but to a greater extent in cells of the liver and intestine. The precursor for cholesterol synthesis is acetyl CoA, which can be produced from glucose, fatty acids, or amino acids. Two molecules of acetyl CoA form ace- toacetyl CoA, which condenses with another molecule of acetyl CoA to form hydroxymethylglutaryl CoA (HMG-CoA). This reaction, catalyzed by HMG-CoA reductase, is the major rate- limiting step of cholesterol synthesis. Mevalonate produces isoprene units that condense, eventually forming squalene. Cyclization of squalene produces the steroid ring system, and a number of subsequent reactions generate cholesterol. The adrenal cortex and the gonads also synthesize cholesterol in significant amounts and use it as a precursor for steroid hormone synthesis. Cholesterol is packaged in chylomicrons in the intestine and in very-low-den- sity lipoprotein (VLDL) in the liver. It is transported in the blood in these lipopro- tein particles, which also transport triacylglycerols. As the triacylglycerols of the blood lipoproteins are digested by lipoprotein lipase, chylomicrons are converted to chylomicron remnants, and VLDL is converted to intermediate-density lipoprotein (IDL) and subsequently to low-density lipoprotein (LDL). These prod- ucts return to the liver, where they bind to receptors in cell membranes and are taken up by endocytosis and digested by lysosomal enzymes. LDL is also endocy- tosed by nonhepatic (peripheral) tissues. Cholesterol and other products of lyso- somal digestion are released into the cellular pools. The liver uses this recycled cholesterol, and the cholesterol that is synthesized from acetyl CoA, to produce VLDL and to synthesize bile salts. Intracellular cholesterol obtained from blood lipoproteins decreases the synthesis of cholesterol within cells, stimulates the storage of cholesterol as cholesterol esters, and decreases the synthesis of LDL receptors.

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In the example of secondary structures cytoskeleton (see Chapter 10) purchase cialis super active 20mg fast delivery. This fold is a binding site for NAD or safe cialis super active 20 mg, in other proteins cialis super active 20 mg with amex, ing to the G-actin subunits promotes their molecules with a generally similar structure (e 20mg cialis super active free shipping. However order cialis super active 20 mg overnight delivery, many pro- addition to the growing ends of the F-actin polymers. Hydrolysis of bound ATP to ADP teins that bind NAD or NADP contain a very different fold from a separate fold family. These two different NAD binding folds arise from different ancestral lines by the G-actin subunit promotes dissocia- and have different structures, but have similar properties and function. The Solubility of Globular Proteins in an Aqueous Environment Most globular proteins are soluble in the cell. In general, the core of a globular domain has a high content of amino acids with nonpolar side chains (val, leu, ile, met, and phe), out of contact with the aqueous medium. This hydrophobic core is densely packed to maximize attractive van der Waals forces, which exert themselves over short distances. The charged polar amino acid side chains (arg, his, lys, asp, and glu) are generally located on the surface of the protein, where they form ion pairs (salt bridges) or are in contact with aqueous solvent. When charged amino acids are located on the interior, they are generally involved in forming specific binding sites. The polar uncharged amino acid side chains of ser, thr, asn, gln, tyr, and trp are also usually found on the surface of the protein, but may occur in the interior, hydrogen bonded to other side chains. Although cystine disulfide bonds (the bond formed by two cysteine sulfhydryl groups) are sometimes involved in the formation of tertiary structure, they are gen- erally not needed. Tertiary Structure of Transmembrane Proteins ( 2-adrenergic) receptor are typical of hormone receptors. Each extra- Transmembrane proteins, such as the 2-adrenergic receptor, contain mem- cellular loop is actually a structural domain, brane-spanning domains and intracellular and extracellular domains on either but several loops together form the binding side of the membrane (Fig. Many ion channel proteins, transport proteins, site for the hormone. The binding site is neurotransmitter receptors, and hormone receptors contain similar membrane- sometimes referred to as a binding domain spanning segments that are -helices with hydrophobic residues exposed to the (a functional domain), even though it is not lipid bilayer. These rigid helices are connected by loops containing hydrophilic formed from a continuous segment of the amino acid side chains that extend into the aqueous medium on both sides of the polypeptide chain. In the 2-adrenergic receptor, the helices clump together so that the (residues 1–34) extends out of the membrane extracellular loops form a surface that acts as a binding site for the hormone and has branched high mannose oligosac- charides linked through N-glycosidic bonds adrenaline (epinephrine), our fight or flight hormone. The binding site is some- to the amide of asparagine. It is anchored in times referred to as a binding domain (a functional domain), even though it is the lipid plasma membrane by a palmitoyl not formed from a continuous segment of the polypeptide chain. The COOH terminus, which extends site for another signaling protein, a heterotrimeric G protein (a guanosine into the cytoplasm, has a number of serine triphosphate [GTP]-binding protein composed of three different subunits). As discussed in Chapter 6, transmembrane proteins usually have a number of posttranslational modifications that provide additional chemical groups to fulfill requirements of the three-dimensional structure. The amino terminus (residues 1–34) extends out of the membrane and has branched high mannose oligosaccha- rides linked through N -glycosidic bonds to the amide of asparagine (see Fig. It is anchored in the lipid plasma membrane by a palmitoyl group that forms a thioester with the SH residue of a cysteine. The COOH terminus, which extends A B Carbohydrate Extracellular side NH2 Carbohydrate Hormone binding domain NH2 Ligand binding domain G-protein binding Regulatory domain phosphorylation sites COOH Phosphorylation sites Cytoplasm G-protein binding domain Fig. The receptor has seven -helix domains that span the membrane and is therefore a member of the heptaheli- cal class of receptors. The transmembrane domains are drawn in an extended form. The seven transmembrane helices (shown as tubes) form a cylindrical structure. Loops connecting helices form the hormone binding site on the external side of the plasma membrane, and a bind- ing site for a G-protein is on the intracellular side. The protein also contains oligosaccharide chains, palmityl groups, and phosphorylation sites (shown in blue; see Chapter 6). CHAPTER 7 / STRUCTURE–FUNCTION RELATIONSHIPS IN PROTEINS 101 into the cytoplasm, has a number of serine and threonine phosphorylation sites Creatine phosphokinase (CK), one (shown as blue circles) that regulate receptor activity. QUATERNARY STRUCTURE imers (two identical subunits of either the M The quaternary structure of a protein refers to the association of individual polypep- [muscle] isozyme or the B [brain] isozyme), tide chain subunits in a geometrically and stoichiometrically specific manner. Many or heterodimers (MB) The MB isozyme is produced only by the heart and readily proteins function in the cell as dimers, tetramers, or oligomers, proteins in which released from injured cardiomyocytes into two, four, or more subunits, respectively, have combined to make one functional the blood (see Chapter 6).

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