Biomedical subjects

J Frank

Publications and source records attributed to J Frank.

At least 127 records · Page 7Linked to original sources

PubMed1999

Structure and structural variations of the Escherichia coli 30 S ribosomal subunit as revealed by three-dimensional cryo-electron microscopy.

A three-dimensional reconstruction of the 30 S subunit of the Escherichia coli ribosome was obtained at 23 A resolution. Because of the improved resolution, many more structural details are seen as compared to those obtained in earlier studies. Thus, the new structure is more suitable for comparison with the 30 S subunit part of the 70 S ribosome, whose structure is already known at a better resolution. In addition, we observe relative and, to some extent, independent movements of three main structural domains of the 30 S subunit, namely head, platform and the main body, which lead to partial blurring of the reconstructed volume. An attempt to subdivide the data set into conformationally defined subsets reveals the existence of conformers in which these domains have different orientations with respect to one another. This result suggests the existence of dynamic properties of the 30 S subunit that might be required for facilitating its interactions with mRNA, tRNA and other ligands during protein biosynthesis.

Bacterial Proteins↗

PubMed1999

Thermally induced aggregation of human transferrin receptor studied by light-scattering techniques.

The thermal stability of transferrin receptor isolated from human placenta in detergent-free solution has been investigated by static light-scattering and photon correlation spectroscopy. In detergent-free solution at 293.2 K, human transferrin receptor (hTfR) forms stable associates with a hydrodynamic radius of 16 nm. With increasing temperature the particles get more compact, above 340 K a phase transition takes, place and spontaneous aggregation of the receptor occurs. Under these conditions large clusters are formed that lead to fractal aggregates, coexisting with dendritic crystalline structures. The experimental findings are compatible with a model, which involves a reaction limited cluster-cluster aggregation mechanism in conjunction with a nucleation process. The molar enthalpy change associated with the phase transition was determined to be (1860 +/- 150) kJ/mol(-1) at a transition temperature of (341.3 +/- 0.2) K.

Biophysical Phenomena↗

PubMed1999

Structural studies of the translational apparatus.

Significant progress is occurring at an accelerated rate in structural studies of ribosomes. A 3D cryoelectron microscopy map of the 70S ribosome from Escherichia coli is available at 15 A resolution and a combination of cryoelectron microscopy with X-ray crystallography has yielded a 9 A resolution map of the 50S subunit from Haloarcula marismortui, an archaebacterium. For eukaryotes, 3D cryomaps of the 80S ribosomes from yeast and from mammals have now been produced at resolutions in the range 20 to 30 A. The most ground-breaking results have been obtained from the 3D mapping of ligands in functional studies of prokaryotic ribosomes. These studies, which directly visualize the protein synthesis machine in action, have brought new excitement to a field that was relatively dormant during the past decade.

Animals↗

PubMed1999

Conformational variability in Escherichia coli 70S ribosome as revealed by 3D cryo-electron microscopy.

During protein biosynthesis, ribosomes are believed to go through a cycle of conformational transitions. We have identified some of the most variable regions of the E. coli 70S ribosome and its subunits, by means of cryo-electron microscopy and three-dimensional (3D) reconstruction. Conformational changes in the smaller 30S subunit are mainly associated with the functionally important domains of the subunit, such as the neck and the platform, as seen by comparison of heat-activated, non-activated and 50S-bound states. In the larger 50S subunit the most variable regions are the L7/L12 stalk, central protuberance and the L1-protein, as observed in various tRNA-70S ribosome complexes. Difference maps calculated between 3D maps of ribosomes help pinpoint the location of ribosomal regions that are most strongly affected by conformational transitions. These results throw direct light on the dynamic behavior of the ribosome and help in understanding the role of these flexible domains in the translation process.

Bacterial Proteins↗

PubMed1999

EF-G-dependent GTP hydrolysis induces translocation accompanied by large conformational changes in the 70S ribosome.

Cryo-electron microscopy has been used to visualize elongation factor G (EF-G) on the 70S ribosome in GDP and GTP states. GTP hydrolysis is required for binding of all the domains of EF-G to the pretranslocational complex and for the completion of translocation. In addition, large conformational changes have been identified in the ribosome. The head of the 30S subunit shifts toward the L1 protein side, and the L7/L12 stalk becomes bifurcated upon EF-G binding. Upon GTP hydrolysis, the bifurcation is reversed and an arc-like connection is formed between the base of the stalk and EF-G.

Cryoelectron Microscopy↗

PubMed1999

Mutations in the translation initiation codon of the protoporphyrinogen oxidase gene underlie variegate porphyria.

Variegate porphyria (VP), one of the acute hepatic porphyrias, is characterized by a reduced catalytic activity of protoporphyrinogen oxidase (PPO), the penultimate enzyme in the porphyrin-haem biosynthetic pathway. VP has been linked to the PPO gene on chromosome 1q22-23, and several mutations underlying this disorder have been described recently. In this study, we identified two different missense mutations in the translation initiation codon of the PPO gene in two unrelated patients with VP. Mutation analysis was carried out using PCR, heteroduplex analysis, automated sequencing, and restriction enzyme digestion. In the first patient, the results revealed an A-to-T transversion (ATG --> TTG), resulting in the substitution of methionine by leucine (M1L). The mutation detected in the second patient was a T-to-C transition (ATG --> ACG), leading to the conversion of methionine to threonine (M1T). These mutations abolish the initiation of translation at the normal site, and consequently, translation of an abnormal messenger RNA (mRNA) would result in the synthesis of a truncated PPO protein lacking the amino terminus.

Adenosine↗

PubMed1999

Proposal of a new electromechanical total artificial heart: the TAH Serpentina.

A new type of energy converter for an electro-mechanical total artificial heart (TAH) based on the principle of a unidirectional moving motor is described. Named the TAH Serpentina, the concept consists of 2 major parts, a pendulum shaped movable element fixed on one side using a joint bearing and a special shaped drum cam. Pusher plates are mounted flexibly to the crossbar of the pendulum. A motor drives the special shaped drum cam linked to the pendulum through a ball bearing. The circular motion of the unidirectional moving brushless DC motor is transferred into the linear motion of the pendulum to drive the pusher plates. Using a crossbar with a variable length, the stroke of the pendulum and therefore the displaced blood volume is alterable. To achieve a variable length, an electric driven screw thread or a hydraulic system is possible. Comparable to the natural heart, cardiac output would be determined by frequency and stroke volume.

Electronics, Medical↗

PubMed1999

An animal model to study microcirculatory changes associated with vascular delay.

Vascular delay is a surgical procedure that renders a flap partially ischaemic several days prior to its transfer in order to increase its viability after its transfer. Though much debate exists regarding the actual mechanism of vascular delay, most theories agree that changes in the microcirculation play a key role. In this paper, we describe four experiments that establish the ear of the homozygous (hr/hr) hairless mouse as an effective model for directly viewing and measuring delay-induced changes in microcirculation. In our first experiment, we compared mouse ears that were delayed (n = 18) with ones that were not (control) (n = 13) and showed that vascular delay significantly (P < 0.05) reduced ear flap necrosis. In a second experiment, we delayed mouse ears for 2 (n = 9), 4 (n = 14), 6 (n = 10), 8 (n = 10), 10 (n = 10), 20 (n = 18), 40 (n = 10) and 80 (n = 11) days and found that the reduction in necrosis becomes statistically significant (P < 0.05) over non-delayed controls (n = 12) after a minimum delay period of 6 days. In a third experiment, we delayed mouse ears by ligating only the vein (n = 14), only the artery (n = 11), only the nerve (sympathectomy) (n = 14), and vein, artery and nerve (n = 14) of the main neurovascular pedicle and found significant (P < 0.05) reductions in flap necrosis in all groups compared to nondelayed controls (n = 12). Finally, in a fourth experiment, we measured vessel directionality changes in mouse ears that were delayed for 6 (n = 4), 10 (n = 4), 20 (n = 4), 40 (n = 4) and 80 (n = 4) days, and found that directionality changes became significant (P < 0.05) at 6 days of delay and remained so for all the days studied when compared with non-delayed controls (n = 4).

Animals↗

PubMed1999

Biochemical but not clinical vitamin A deficiency results from mutations in the gene for retinol binding protein.

BACKGROUND: Two German sisters aged 14 and 17 y were admitted to the Tübingen eye hospital with a history of night blindness. In both siblings, plasma retinol binding protein (RBP) concentrations were below the limit of detection (<0.6 micromol/L) and plasma retinol concentrations were extremely low (0.19 micromol/L). Interestingly, intestinal absorption of retinyl esters was normal. In addition, other factors associated with low retinol concentrations (eg, low plasma transthyretin or zinc concentrations or mutations in the transthyretin gene) were not present. Neither sibling had a history of systemic disease. OBJECTIVE: Our aim was to investigate the cause of the retinol deficiency in these 2 siblings. DESIGN: The 2 siblings and their mother were examined clinically, including administration of the relative-dose-response test, DNA sequencing of the RBP gene, and routine laboratory testing. RESULTS: Genomic DNA sequence analysis revealed 2 point mutations in the RBP gene: a T-to-A substitution at nucleotide 1282 of exon 3 and a G-to-A substitution at nucleotide 1549 of exon 4. These mutations resulted in amino acid substitutions of asparagine for isoleucine at position 41 (Ile41-->Asn) and of aspartate for glycine at position 74 (Gly74-->Asp). Sequence analysis of cloned polymerase chain reaction products spanning exons 3 and 4 showed that these mutations were localized on different alleles. The genetic defect induced severe biochemical vitamin A deficiency but only mild clinical symptoms (night blindness and a modest retinal dystrophy without effects on growth). CONCLUSIONS: We conclude that the cellular supply of vitamin A to target tissues might be bypassed in these siblings via circulating retinyl esters, beta-carotene, or retinoic acid, thereby maintaining the health of peripheral tissues.

Adolescent↗

PubMed1999

Sensory organization for balance: specific deficits in Alzheimer's but not in Parkinson's disease.

BACKGROUND: The cause of frequent falling in patients with dementia of the Alzheimer type (AD) is not well understood. Distraction from incongruent visual stimuli may be an important factor as suggested by their poor performance in tests of shifting visual attention in other studies. The purpose of this study was to determine whether AD patients have difficulty maintaining upright balance under absent and/or incongruent visual and other sensory conditions compared to nondemented healthy elderly persons and individuals with Parkinson's disease (PD). METHODS: Seventeen healthy older adults, 15 medicated PD subjects, and 11 AD subjects underwent the Sensory Organization Test protocol. The incidence of loss of balance ("falls"), and the peak-to-peak amplitude of body center of mass sway during stance in the six sensory conditions were used to infer the ability to use visual, somatosensory, and vestibular signals when they provided useful information for balance, and to suppress them when they were incongruent as an orientation reference. Vestibular reflex tests were conducted to ensure normal vestibular function in the subjects. RESULTS: AD subjects had normal vestibular function but had trouble using it in condition 6, where they had to concurrently suppress both incongruent visual and somatosensory inputs. All 11 AD subjects fell in the first trial of this condition. With repeated trials, only three AD subjects were able to stay balanced. AD subjects were able to keep their balance when only somatosensory input was incongruent. In this condition, all AD subjects were able to maintain balance whereas some falls occurred in the other groups. In all conditions, when AD subjects did not fall, they were able to control as large a sway as the healthy controls, except when standing with eyes closed in condition 2: AD subjects did not increase their sway whereas the other groups did. In the PD group, the total fall incidence was similar to the AD group, but the distribution was generalized across more sensory conditions. PD subjects were also able to improve with repeated trials in condition 6. CONCLUSION: Patients with dementia of the Alzheimer type have decreased ability to suppress incongruent visual stimuli when trying to maintain balance. However, they did not seem to be dependent on vision for balance because they did not increase their sway when vision was absent. Parkinsonian patients have a more general balance control problem in the sensory organization test, possibly related to difficulty changing set.

Accidental Falls↗

PubMed1999

Comparison of dacryocystography and lacrimal scintigraphy in the diagnosis of functional nasolacrimal duct obstruction.

AIM: It appears from the literature that no standardised examination exists for patients with functional nasolacrimal duct obstruction. The role of dacryocystography and lacrimal scintigraphy was compared in the diagnosis and management of these patients. METHOD: Patients who were clinically diagnosed as having unilateral or bilateral functional nasolacrimal duct obstruction were prospectively entered into the study and data collected over 12 months in Moorfields Eye Hospital and Whipps Cross Hospital, London. All cases had, on separate occasions, a standardised dacryocystogram with delayed erect films and a lacrimal drainage scintigram. RESULTS: 45 lacrimal systems of 32 patients (mean age 62 years; 59% male) fulfilled the inclusion criteria. Abnormalities were detected with dacryocystography in 93% of systems and with lacrimal drainage scintigraphy in 95% of systems. Based on the results of previous quantitative studies, the positive scintigrams were subdivided into those demonstrating prelacrimal sac delay (13%), delay at the lacrimal sac/duct junction (35%), or delay within the duct (47%). Combining the two imaging techniques increased the sensitivity to 98%. CONCLUSIONS: Both investigations are very sensitive at detecting abnormalities in patients with a clinical diagnosis of functional nasolacrimal duct obstruction. Lacrimal drainage scintigraphy is a slightly more sensitive test, but missed an abnormality detected by dacryocystography in two (4%) systems. A combination of the two techniques gives the highest sensitivity with maximum anatomical and physiological information but, in clinical practice, it is reasonable to perform a dacryocystogram initially and proceed to scintigraphy only if contrast radiography is normal.

Adult↗

PubMed1999

Are risk factors for atherothrombotic disease associated with back pain sickness absence? The Whitehall II Study.

STUDY OBJECTIVE: To explore the previously stated hypothesis that risk factors for atherothrombotic disease are associated with back pain. DESIGN: Prospective (mean of four years of follow up) and retrospective analyses using two main outcome measures: (a) short (< or = 7 days) and long (> 7 days) spells of sickness absence because of back pain reported separately in men and women; (b) consistency of effect across the resulting four duration of spell and sex cells. SETTING: 14 civil service departments in London. PARTICIPANTS: 3506 male and 1380 female white office-based civil servants, aged 35-55 years at baseline. MAIN RESULTS: In age adjusted models, low apo AI was associated with back pain across all four duration-sex cells and smoking was associated across three cells. Six factors were associated with back pain in two cells: low exercise and high BMI, waist-hip ratio, triglycerides, insulin and Lp(a). On full adjustment (for age, BMI, employment grade and back pain at baseline), each of these factors retained a statistically significant effect in at least one duration-sex cell. Triglycerides were associated with short and long spells of sickness absence because of back pain in men in fully adjusted models with rate ratios (95% confidence intervals) of 1.53 (1.1, 2.1) and 1.75 (1.0, 3.2) respectively. There was little or no evidence of association in age adjusted models with: fibrinogen, glucose tolerance, total cholesterol, apoB, hypertension, factor VII, von Willebrand factor, electrocardiographic evidence of coronary heart disease and reported angina. CONCLUSIONS: In this population of office workers, only modest support was found for an atherothrombotic component to back pain sickness absence. However, the young age of participants at baseline and the lack of distinction between different types of back pain are likely to bias the findings toward null. Further research is required to ascertain whether a population sub-group of atherothrombotic back pain can be identified.

Absenteeism↗

PubMed1999

Comparison of four peak spinal loading exposure measurement methods and their association with low-back pain.

OBJECTIVES: This paper examines the performance of 4 different methods of estimating peak spinal loading and their relationship with the reporting of low-back pain. METHODS: The data used for this comparison was a subset of subjects from a case-referent study of low-back-pain reporting in the automotive industry, in which 130 random referents and 105 cases (or job-matched proxies) were studied. The peak load on the lumbar spine was determined using a biomechanical model with model inputs coming from a detailed self-report questionnaire, a task-based check list, a video digitization method, and a posture and load sampling technique. RESULTS: The methods were directly comparable through a common metric of newtons or newton meters of spinal loading in compression, shear, or moment modes. All the methods showed significant and substantial associations with low-back pain in all modes (odds ratios 1.6-2.3). The intraclass correlation coefficients (ICC) showed strong similarities between the checklist and video digitized techniques (ICC 0.84-0.91), moderate similarities between these techniques and the work sampling method (ICC 0.49-0.52), and poor correlations (ICC 0.16-0.40) between the self-report questionnaire and the observer recorded measures. CONCLUSIONS: While all the methods detected significant odds ratios, they cannot all be used interchangeably for risk assessment at the individual level. Peak spinal compression, moment, and shear are important risk factors for low-back pain reporting, no matter which measurement method is used. Questionnaires can be used for large-scale studies. At the individual level a task-based checklist provides biomechanical model inputs at lower cost and equal performance compared with the criterion video digitization system.

Biomechanical Phenomena↗

PubMed1999

Erythropoietic protoporphyria: identification of novel mutations in the ferrochelatase gene and comparison of biochemical markers versus molecular analysis as diagnostic strategies.

BACKGROUND: Erythropoietic protoporphyria (EPP) results from an inherited deficiency of the last enzyme of the heme biosynthetic pathway, ferrochelatase (FC). EPP is usually inherited in an autosomal dominant fashion, and the mutations in the FC gene on chromosome 18q21.3 detected in EPP patients are heterogeneous. METHODS: In this study, we screened the FC gene for mutations in 12 patients from 10 unrelated families with EPP and their family members using heteroduplex analysis, automated sequencing, and restriction enzyme digestion. RESULTS: We detected 8 different mutations in these patients, including 1 missense mutation, 5 frameshift mutations, and 2 splice site mutations, 6 of which are previously undescribed. CONCLUSIONS: We have established the molecular basis of EPP in 10 unrelated families, thereby providing further evidence for the heterogeneity in this disorder. Importantly, molecular diagnosis allowed revisions in the status of several clinically unaffected silent mutation carriers within the families. We compare the value of genetic research strategies with the combination of biochemical data and clinical phenotype as diagnostic tools to confirm a putative diagnosis in EPP.

Biomarkers↗

PubMed1999

[Value of MRI in diagnosis of post-traumatic wrist complaints].

The diagnostic value of MRI in acute and chronic posttraumatic wrist pain will be demonstrated in several clinical cases. The integration of MRI in a diagnostic algorithm is discussed. The indication of MRI is given for suspected complex ligamentous lesions, occult fractures and soft tissue pathologies, in particular with disconcordant clinical and radiological signs. Pathology orientated study protocols are presented. Preoperatively, MRI will be helpful in planning definitive surgical treatment.

Fractures, Bone↗

PubMed1999

[Diagnostic and therapeutic significance of arthroscopy in distal radius fracture].

Non-operative and minimal-invasive treatment of distal radius fractures have still a poor outcome. Although bony structures often heal acceptable, additional lesions of intraarticular ligamentous structures cause persistent pain and disability. Aim of the study was to present the diagnostic and therapeutic possibilities of arthroscopically assisted treatment of distal radius fractures. Diagnostic wrist arthroscopy found in 6 of 30 patients with distal radius fractures (23 AO type C fractures) a scapho-lunate ligament tear (20%) of which 3 had to be stabilized operatively. 18 patients (60%) presented with tears of the triangular fibrocartilage complex [Palmer classification: 1A (1); 1B (5); 1D (2); 1A, 1B (2); 1A, 1D (6); 1B, 1D (2)], which were repaired by arthroscopic shaving (n = 12), Kirschner wire stabilization of ulna head (n = 2) or arthroscopic suture (n = 3). Fractures were stabilized in most cases by combinations of canulated titan screws (3.0 mm) and Kirschner wires (n = 12). In 27 patients, the radial joint surface and the distal radio-ulnar joint could be reconstructed without any specific complications. Arthroscopic reduction of distal radius fractures allows minimal-invasive reconstruction of the joint surface, diagnoses relevant ligamentous tears and should applied with incongruencies of the joint surface greater than 2 mm and in widely dislocated fractures.

Adult↗

PubMed1999

Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.

PURPOSE: To describe the phenotype caused by a retinol deficiency in a family with compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP). METHODS: The two affected sisters, 17 (BR) and 13 (MR) years old, were examined clinically and with perimetry, color vision tests, dark adaptometry, rod- and cone-isolated electroretinograms (ERGs), multifocal ERGs, electrooculograms (EOGs), and laboratory tests. RESULTS: There were no complaints besides night vision problems and no history of systemic disease. Visual acuity was reduced to 20/40 (BR) and 20/25 (MR). Anterior segments were normal except for a discrete iris coloboma. Both patients showed a typical "fundus xerophthalmicus," featuring a progressed atrophy of the retinal pigment epithelium. Dark adaptation thresholds were elevated. In the scotopic ERG, only reduced mixed responses were recordable. The photopic ERG was reduced in BR and normal in MR; implicit times were highly (BR) to slightly (MR) elevated. There was no (BR) to little (MR) light reaction in the EOG. All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test. RBP was below detection threshold, and retinyl esters were normal. CONCLUSIONS: Both affected siblings had no detectable serum RBP, one sixth of normal retinol levels, and normal retinyl esters. The retinal pigment epithelium was severely affected, but besides acne there were no changes to other organs. This gives evidence for an alternative tissue source of vitamin A, presumably retinyl esters from chylomicron remnants. The normal retinol levels in the tear fluid explain the lack of xerophthalmia. However, considering the role of RBP in the tear fluid and, during development, in the yolk sac there is also evidence that there are organ-specific RBP forms not affected by the genetic defect.

Adolescent↗

PubMed1998

The ribosome-structure and functional ligand-binding experiments using cryo-electron microscopy.

Cryo-electron microscopy has greatly advanced our understanding of the basic steps of protein synthesis in the bacterial ribosome. This article gives an overview of what has been achieved so far. Through three-dimensional visualization of complexes that represent the ribosome in defined binding states, locations were derived for the tRNA in A, P, and E sites, as well as the elongation factors. In addition, the pathways of messenger RNA and the exiting polypeptide chain could be inferred.

Bacterial Proteins↗