By J. Ugolf. National American University.
TERTIARY STRUCTURE tant features of protein structure buy 25mg clomiphene amex. Although every portion of every The tertiary structure of a protein is the folding pattern of the secondary structural amino acid in a protein is engaged in bond- elements into a three-dimensional conformation cheap 50 mg clomiphene with amex, as shown for the LDH domain in ing to the rest of the protein, to water, or to Figure 7. As illustrated with examples below, this three-dimensional structure is a ligand, proteins do not have rigid struc- designed to serve all aspects of the protein’s function. The three-dimensional structure is ble binding sites for ligands (the compound that binds), illustrated with actin and flexible and dynamic, with rapidly fluctuat- myoglobin. The tertiary structure also maintains residues on the surface appropriate ing movement in the exact position of amino for the protein’s cellular location, polar residues for cytosolic proteins, and acid side chains and domains. These fluctu- hydrophobic residues for transmembrane proteins (illustrated with the 2-adrenergic ations are like wiggling or shaking that can receptor). They allow ions and water to diffuse through the structure and provide alternate conformations for A. The tertiary structure of large complex proteins is often described in terms of physically independent regions called structural domains. You can usually iden- tify domains from visual examination of a three-dimensional figure of a protein, such as the three-dimensional figure of G-actin shown in Fig. Each domain is formed from a continuous sequence of amino acids in the polypeptide chain that are folded into a three-dimensional structure independently of the rest of the protein, and two domains are connected through a simpler structure like a loop (e. The structural features of each domain can be discussed independently of another domain in the same protein, and the struc- tural features of one domain may not match that of other domains in the same protein. Subdomain 4 (IIb) Subdomain 2 (Ib) C Hinge N region Subdomain 3 (IIa) Subdomain 1 (Ia) Fig. The two domains that form the cleft are further subdivided into subdomains 1–4. The overall structure is found in many ATP- binding proteins and is called the actin fold. The conformations of the regions shown in blue are nearly superimposable among the proteins that contain the actin fold. Folds in Globular Proteins More than 1000 folds have now been recognized, and it is pre- Folds are relatively large patterns of three-dimensional structure that have been rec- dicted that there are only a few ognized in many proteins, including proteins from different branches of the phylo- thousand different folds for all the proteins genetic tree. A characteristic activity is associated with each fold, such as ATP bind- that have ever existed. One of the values of ing and hydrolysis (the actin fold) or NAD binding (the nucleotide-binding fold). THE ACTIN FOLD many proteins involved in inherited diseases In the three-dimensional drawing of G-actin shown in Figure 7. However, the function of a domain in a pro- mains contribute to a folding pattern called the actin fold, named for the first pro- tein can be predicted if its amino acid tein in which it was described. ATP is bound into the middle of the cleft of the actin sequence can be matched to that of other fold by amino acid residues contributed by domains on both sides; thus, ATP bind- proteins in a fold family with a known func- ing promotes a conformational change that closes the cleft. Classifying proteins into fold families cleaved to ADP and phosphate. The The actin fold is found in proteins as diverse as actin, which polymerizes to form structure of a bacterial protein targeted by a the cytoskeleton, heat shock protein 70 (hsp70), which uses ATP energy in chang- drug can be compared with that of human ing the conformation of other proteins and hexokinase, which catalyzes phosphory- proteins in the same fold family so that an lation of glucose (see Chapter 8 for further discussion of hexokinase. The amount of sequence identity they do have is consistent with their membership in the same fold family and establishes that they are all homologs of the same ancestral protein. In all of these proteins, ATP binding results in large conformational changes that contribute to the function of the protein. THE NUCLEOTIDE BINDING FOLD G-actin subunits polymerize to form F-actin, which forms the A fold also can be formed by one domain. In the example of secondary structures cytoskeleton (see Chapter 10). This fold is a binding site for NAD or, in other proteins, ing to the G-actin subunits promotes their molecules with a generally similar structure (e.
The rigidity of the peptide backbone the quarternary structure of hemoglobin and determines the types of secondary structure that can occur buy cheap clomiphene 25 mg on-line. The tertiary structure its solubility generic clomiphene 25mg online, and not its ability to bind oxy- involves folding of the secondary structural elements into an overall three-dimen- gen. In globular proteins such as myoglobin, the tertiary struc- ture generally forms a densely packed hydrophobic core with polar amino acid side chains on the outside. Some proteins exhibit quaternary structure, the combi- nation of two or more subunits, each composed of a polypeptide chain. The tertiary structure of a globular protein is made up of structural domains, regions of structure that are recognized as separate and linked to other domains in a simple way. Within a domain, a combination of secondary Alanine Glycine Serine Valine Leucine Lysine Glycine Valine Primary Secondary Tertiary Quaternary Fig. Folds are defined by their similarity in a number of different proteins. Assembly of globular polypeptide subunits into a multi- subunit complex can provide the opportunity for cooperative binding of ligands (e. The polypeptide chains of fibrous proteins such as collagen are aligned along an axis, have repeating elements, and are extensively linked to each other through hydrogen bonds. Proteins form binding sites for a specific molecule, called a ligand (e. The affinity of a binding site for its ligand is quantitatively characterized by an association or affinity constant, Ka, (or its dissociation constant, Kd). The primary structure of a protein dictates the way that it folds into its tertiary structure, which is a stable conformation that is identical to the shape of other molecules of the same protein (that is, its native conformation. Prion proteins cause neurodegenerative diseases by acting as a tem- plate for misfolding. Heat, acid, and other agents cause proteins to denature, that is, to unfold or refold and lose their native three-dimensional conformation. THE WAITING ROOM Will Sichel, who has sickle cell anemia, was readmitted to the hospital with symptoms indicating that he was experiencing another sickle cell cri- sis (see Chapter 6). Anne Jeina is a 54-year-old woman who arrived in the hospital 4 days ago, approximately 5 hours after she began to feel chest pain (see Chapter 6). In the emergency room, the physician had drawn blood for the measure- ment of myoglobin, CK-MB (creatine kinase, muscle-brain fraction) and cTN-T (cardiac troponin T subunit). The results from these tests had supported the diagno- sis of an acute MI (myocardial infarction), and Mrs. Amy Lloyd is a 62-year-old woman who presents with weakness, fatigue, an Amyloidosis is a term encompass- enlarged tongue (macroglossia), and edema. She has signs and symptoms of ing many diseases that share a common feature—the extracellular cardiac failure, including electrocardiographic abnormalities. Initial labora- deposition of pathologic insoluble fibrillar tory studies showed a serum creatinine of 1. A urinalysis indicated the presence of a moder- sues. In Amy Lloyd‘s disease, amyloido- ate proteinuria and numerous white blood cells in the urinary sediment. She was sub- sis/AL, the amyloid is derived from sequently diagnosed with amyloidosis/AL secondary to a plasma cell dyscrasia. Di Abietes returned to her physician’s office for a routine visit to monitor her treatment (see Chapters 4, 5, and 6. GENERAL CHARACTERISTICS OF THREE-DIMENSIONAL STRUCTURE The overall conformation of a protein, the particular position of the amino acid side chains in three-dimensional space, gives a protein its function. Descriptions of Protein Structure Proteins are generally grouped into major structural classifications: globular proteins, fibrous proteins, transmembrane proteins, and DNA-binding proteins (Fig. Globular proteins are usually soluble in aqueous medium and resemble irregular balls. The fibrous proteins are geometrically linear, arranged around a single axis, and have Globular a repeating unit structure. Another general classification, transmembrane proteins, consists of proteins that have one or more regions aligned to cross the lipid membrane.
Oral and genital pain syndromes in Parkinson’s disease cheap clomiphene 100 mg free shipping. Cognitive and behavioral aspects of basal ganglia disorders buy clomiphene 100 mg with mastercard. Philadelphia: Lippincott Williams and Wilkins, 2002. Hemiparkinsonism-hetniatrophy syndrome: clinical and neuroradiologic features. Bulpitt CJ, Shaw K, Clifton P, Stenn G, Davies JB, Reid IL. The symptoms of patients treated for Parkinson’s disease. Symptoms and duration of the prodromal phase in Parkinson’s disease. The evolution of diagnosis in early Parkinson disease. The accuracy of diagnosis of parkinsonian syndromes in a specialist movement disorder service. Variable expression of Parkinson’s disease: a base-line analysis of the DATATOP cohort. Motor function in the normal aging population: treatment with levodopa. Jankovic J, Ben-Arie L, Schwartz K, Chen K, Kahn K, Lai EC, Krauss JK, Grossman R. Movement and reaction times and ﬁne coordination tasks following pallidotomy. Bagheri H, Damase-Michel C, Lapeyre-Mestre M, et al. A study of salivary secretion in Parkinson’s disease. Teulings H-L, Contreras-Vidal JL, Stelmach GE, Adler CH. Adaptation of handwriting size under distorted visual feedback in patients with Parkinson’s disease and elderly and young controls. Cognition and the basal ganglia: separating mental and motor components of performance in Parkinson’s disease. Quantitative assessment of parkinsonian and essential tremor: clinical application of triaxial accelerometry. Baroni A, Benvenuti F, Fantini L, Pantaleo T, Urbani F. Human ballistic arm abduction movements: effects of L-dopa treatment in Parkinson’s disease. Regional brain dopamine metabolism: a marker for the speed, direction, and posture of moving animals. Which clinical sign of Parkinson’s disease best reﬂects the nigrostriatal lesion? Reversal of experimental parkinson- ism by lesions of the subthalamic nucleus. The globus pallidus, deep brain stimulation and Parkinson’s disease. Levy R, Ashby P, Hutchison WD, Lang AE, Lozano AM, Dostrovsky JO. Dependence of subthalamic nucleus oscillations on movement and dopamine in Parkinson’s disease. Recent physiological and pathophysiological aspects of parkinso- nian movement disorders. The Bereitschaftpotential is abnormal in Parkinson’s disease. Tatton WG, Eastovan MJ, Bedingham W, Verrier MC, Bruce IC. Defective utilization of sensory input as the basis for bradykinesia, rigidity and Copyright 2003 by Marcel Dekker, Inc. Perceptual motor dysfunction in Parkinson’s disease: a deﬁcit in sequential and predictive voluntary movement.
These studies used the terminology ‘‘ventrolateral’’ thalamotomy discount 100mg clomiphene free shipping. More recently buy clomiphene 100 mg lowest price, the records of 42 patients with PD who underwent thalamotomy were reviewed, and 86% had cessation of or moderate-to- marked improvement in their contralateral tremor, with a concomitant improvement in function which persisted for as long as 13 years. The mean daily dose of levodopa was reduced by 156 mg and lesion location was in the Vim (102). Postoperatively, rigidity improved by 30%, ipsilateral tremor worsened, and there was no signiﬁcant change in other features of parkinsonism. The complication rates of unilateral thalamotomy range from 10% transient confusion and 8% facial weakness or numbness (33), to 58% transient and 23% persistent complications of contralateral weakness, Copyright 2003 by Marcel Dekker, Inc. Twenty-two of the 36 (61%) in the series of Fox et al. Half of these cleared by 7 days and only 6% were permanent or bothersome, including dysarthria, dyspraxia, or cognitive dysfunction (100). Deﬁcits of verbal memory are more common after left thalamotomy compared with right thalamotomy (103). One study compared the short-term safety and efﬁcacy of Vim thalamotomy with Vim stimulation (104). Cessation or improved tremor resolution was detected in 79% of the lesioned group compared with 90% in the stimulated group. These results were not statistically different, but only 18% of the lesioned group had an improved functional status compared with 55% of the stimulated group. Additionally, the complication rate for the stimulated group was 16% compared with 47% in the lesioned group, but there was one death in the stimulated group. These positive and negative effects of thalamotomy and thalamic DBS are very similar to a retrospective report comparing the two treatments (105), in which it was additionally shown that tremor recurrence occurred in 15% of patients with thalamot- omy, but only in 5% of patients with DBS. Consequently, 15% of patients with thalamotomy required reoperation. These studies show the expected improved morbidity of DBS compared with irreversible lesioning. However, long-term follow-up (up to 40 months) has highlighted the potential hardware complications of DBS, which include lead fracture, erosion or migration, infection, cerebral spinal ﬂuid (CSF) leak, short or open circuits, or other system malfunctions (106). In one study the mean time to the ﬁrst complication was 10 months (107). From these studies it is estimated that 25–40% of patients with deep brain stimulators may require further surgery to maintain good clinical outcome (106–108). Further long-term compara- tive studies are necessary to deﬁne whether the potential short-term reduction of side effects of DBS outweighs the higher long-term need for re-operation as a result of hardware failure. The Vim nucleus is proposed to be the cerebellar recipient nucleus of the thalamus, and so the effect on tremor may have a different physiological basis from the improvement of bradykinesia and dyskinesia that accompany internal pallidotomy. It is proposed that internal pallidotomy affects the thalamic nuclei that receive inputs from the basal ganglia (Voa and Vop). One factor that therefore continues to confound our understanding of thalamotomy is the variability of lesion locations across series. This is more problematic than with pallidotomy since the boundaries of the thalamic nuclei are not as well demarcated anatomically as in the pallidal complex and the nomenclature of the thalamic nuclei varies across series and also from human to primate (Figs. The above studies support a role for Vim thalamotomy in patients whose predominant symptom is medically intractable asymmetrical tremor Copyright 2003 by Marcel Dekker, Inc. FIGURE 4 Stereotactic trajectory targeting the subthalamic nucleus (STN) and showing the relative positions of the thalamic nuclei Voa, Vop and Vim, the Zona incerta (ZI), the substantia nigra (SNr) and the commissural plane. AC ¼ anterior commissure, PC ¼ posterior commissure, mcp ¼ mid commissural point, Hpth ¼ hypothalamus, IC ¼ internal capsule. The majority of patients with PD are, however, likely to have progressive bradykinesia, even if this is not present at the time of presentation for surgery. This symptom is not modiﬁed by Vim thalamotomy, and so thalamotomy (and Vim DBS) in the treatment of PD has largely been replaced by alternative therapies. Thalamic Targets Other Than Vim It would not be predicted from the known anatomical circuits that Vim thalamotomy would improve dyskinesia, and yet there are reports of this. The location of these antidyskinetic lesions may not have been conﬁned to Vim Copyright 2003 by Marcel Dekker, Inc. The antidyskinetic ﬁndings have also been replicated in experimental monkeys in which thalamotomy was stereotaxically tailored to the thalamic nuclei that receive afferents from the internal pallidum (109) and shown to abolish contralateral chorea but not dystonia.
To do this cheap clomiphene 100mg amex, a Other measurements used to clas- sufficient concentration of hemoglobin in the red blood cells is necessary for effi- sify the type of anemia present cient oxygen delivery to occur 50mg clomiphene amex. When the hemoglobin concentration falls below nor- include the mean corpuscular vol- mal values (Table 44. Anemias can be catego- ume (MCV) and the mean corpuscular hemoglobin concentration (MCHC). The rized based on red cell size and hemoglobin concentration. Red cells can be of MCV is the average volume of the red blood normal size (normocytic), small (microcytic), or large (macrocytic). Cells contain- cell, expressed in femto (10 15) liters. Nor- ing a normal hemoglobin concentration are termed normochromic; those with mal MCV range from 80 to 100 fL. This classification system provides is the average concentration of hemoglobin important diagnostic tools (Table 44. The normal range is 32 to 37; a value of less than 32 would indicate hypochromic cells. ERYTHROCYTE METABOLISM blood cells have an MCV of less than 80 and an MCHC of less than 32. The Mature Erythrocyte mochromic cells have an MCV of greater To best understand how the erythrocyte can carry out its major function, a discus- than 100, with an MCHC between 32 and 37. Mature erythrocytes contain no intra- cellular organelles, so the metabolic enzymes of the red blood cell are limited to The trace amounts of 2,3 BPG those found in the cytoplasm. In addition to hemoglobin, the cytosol of the red found in cells other than erythro- blood cell contains enzymes necessary for the prevention and repair of damage done cytes is required for the phospho- by reactive oxygen species (see Chapter 24) and the generation of energy glycerate mutase reaction of glycolysis, in which 3-phosphoglycerate is isomerized to (Fig. Erythrocytes can only generate adenosine triphosphate (ATP) by gly- 2-phosphoglycerate. The ATP is used for ion transport across the cell membrane (primarily Na ,K , and Ca 2), the phosphorylation of membrane proteins, and the regenerated during each reaction cycle, it is only required in catalytic amounts. Erythrocyte glycolysis also uses the Rapaport-Lue- bering shunt to generate 2,3-bisphosphoglycerate (2,3-BPG). Red cells contain 4 to 5 mM 2,3-BPG, compared with trace amounts in other cells. As discussed in more detail in Section IV, 2,3-BPG is a modulator of oxygen binding to hemoglobin that stabilizes the deoxy form of hemoglobin, thereby facilitating the release of oxygen to the tissues. To bind oxygen, the iron of hemoglobin must be in the ferrous ( 2) state. Reactive oxygen species can oxidize the iron to the ferric ( 3) state, producing Table 44. Classification of the Anemias on the Basis of Red Cell Morphology Red Cell Morphology Functional Deficit Possible Causes Microcytic, hypochromic Impaired hemoglobin Iron deficiency, thalassemia synthesis mutation, lead poisoning Macrocytic, normochromic Impaired DNA synthesis B12 or folic acid deficiency, erythroleukemia Normocytic, normochromic Red cell loss Acute bleeding, sickle cell disease, red cell metabolic defects, red cell membrane defects CHAPTER44 / THE BIOCHEMISTRY OF THE ERYTHROCYTE AND OTHER BLOOD CELLS 809 Oxidizing Destroyed agent oxidizing agent Reduced Oxidized glutathione glutathione Glucose ADP NADP+ NADPH ATP Glucose-6-P 5-carbon sugars HMP shunt Fructose-6-P ADP ATP Fructose 1,6 BP DHAP Reduced Glyceraldehyde-3-P 3+ cytochrome b5 + Fe -hemoglobin NAD Fe2+-hemoglobin Oxidized NADH mutase cytochrome b5 1,3 bisphosphoglycerate 2,3 BPG cytochrome b5 ADP reductase Rapoport- ATP Luberin shunt 3-phosphoglycerate phosphatase 2-phosphoglycerate PEP ADP ATP Pyruvate NADH NAD+ Lactate Fig. Glycolysis is the major pathway, with branches for the hexose monophosphate shunt (for pro- tection against oxidizing agents) and the Rapoport-Luebering shunt (which generates 2,3 bisphosphoglycerate, which moderates oxygen bind- ing to hemoglobin). The NADH generated from glycolysis can be used to reduce methemoglobin (Fe 3) to normal hemoglobin (Fe 2), or to con- vert pyruvate to lactate, such that NAD can be regenerated and used for glycolysis. Pathways unique to the erythrocyte are indicated in blue. Some of the NADH produced by glycolysis is used to regenerate hemoglobin from methemoglobin by the NADH-cytochrome b5 methemoglobin reductase system. The oxi- 5 dized cytochrome b5 is then reduced by a flavin-containing enzyme, cytochrome b5 reductase (also called methemoglobin reductase), using NADH as the reducing agent. An inherited deficiency in pyruvate kinase leads to hemolytic anemia (an anemia caused by the destruction of red blood cells; hemo- globin values typically drop to 4 to 10 g/dL in this condition). Because the amount of ATP formed from glycolysis is decreased by 50%, red blood cell ion transporters cannot function effectively. The red blood cells tend to gain Ca2 and lose K and water. The water loss increases the intracellular hemoglobin concentration.
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