Analysis of thermal stabilizing interactions in mesophilic and thermophilic adenylate kinases from the genus Methanococcus.

Adenylate kinases (ADKs) from four closely related methanogenic members of the Archaea (the mesophile Methanococcus voltae (MVO), the thermopile Methanococcus thermolithotrophicus (MTH), and the extreme thermopiles Methanococcus igneus (MIG) and Methanococcus jannaschii (MJA)) were characterized for their resistance to thermal denaturation. Despite possessing between 68 and 81% sequence identity, the methanococcal ADKs significantly differed in their stability against thermal denaturation, with melting points ranging from 69 to 103 degrees C. The high sequence identity between these organisms allowed regions of the MVO and MJA ADKs to be exchanged, producing chimeric ADKs with significantly altered thermal stability. Up to a 20 degrees C increase or decrease in stability was achieved for chimeric ADKs, whereas 88% of the original protein sequence was maintained. Based on our previous structural modeling studies, we conclude that cooperative interactions within the hydrophobic protein core play an integral role in determining the differences in structural stability observed between the methanococcal ADKs. From comparisons of the effects of temperature on protein unfolding and optimal enzymatic activity, we also conclude that thermostability and enzymatic temperature optima are influenced differently by molecular modifications and thus that the protein flexibility required for activity and stability, respectively, is not unconditionally linked within the methanococcal ADKs.

Thermal adaptation analyzed by comparison of protein sequences from mesophilic and extremely thermophilic Methanococcus species.

The genome sequence of the extremely thermophilic archaeon Methanococcus jannaschii provides a wealth of data on proteins from a thermophile. In this paper, sequences of 115 proteins from M. jannaschii are compared with their homologs from mesophilic Methanococcus species. Although the growth temperatures of the mesophiles are about 50 degrees C below that of M. jannaschii, their genomic G+C contents are nearly identical. The properties most correlated with the proteins of the thermophile include higher residue volume, higher residue hydrophobicity, more charged amino acids (especially Glu, Arg, and Lys), and fewer uncharged polar residues (Ser, Thr, Asn, and Gln). These are recurring themes, with all trends applying to 83-92% of the proteins for which complete sequences were available. Nearly all of the amino acid replacements most significantly correlated with the temperature change are the same relatively conservative changes observed in all proteins, but in the case of the mesophile/thermophile comparison there is a directional bias. We identify 26 specific pairs of amino acids with a statistically significant (P < 0.01) preferred direction of replacement.

Cysteinyl-tRNA formation: the last puzzle of aminoacyl-tRNA synthesis.

With the exception of the methanogenic archaea Methanococcus jannaschii and Methanobacterium thermoautotrophicum deltaH, all organisms surveyed contain orthologs of Escherichia coli cysteinyl-tRNA synthetase (CysRS). The characterization of CysRS-encoding (cysS) genes and the demonstration of their ability to complement an E. coli cysSts mutant reveal that Methanococcus maripaludis and Methanosarcina barkeri, two other methanogenic archaea, possess canonical CysRS proteins. A molecular phylogeny inferred from 40 CysRS sequences indicates that the CysRS of M. maripaludis and Methanosarcina spp. are specific relatives of the CysRS of Pyrococcus spp. and Chlamydia, respectively. This result suggests that the CysRS gene was acquired by lateral gene transfer in at least one euryarchaeotic lineage.

Anomalies of pulmonary veins: usefulness of spin-echo and gradient-echo MR images.

OBJECTIVE: We compared the value of spin-echo and gradient-echo MR images in the evaluation of anomalies of pulmonary veins. MATERIALS AND METHODS: Fourteen patients with a variety of developmental anomalies of pulmonary veins underwent MR imaging examination. Axial T1-weighted spin-echo and gradient-echo MR images were evaluated retrospectively on separate occasions during which visualization of normal and anomalous pulmonary veins was determined. RESULTS: Of 52 pulmonary veins, 46 (88%) were identified on T1-weighted spin-echo images and 50 (96%) on gradient-echo images. Two patients had atresia of both left pulmonary veins. Of 14 anomalous veins, 11 (79%) were revealed on spin-echo images and 13 (93%) on gradient-echo images. CONCLUSION: Both spin-echo and gradient-echo MR images were accurate in revealing anomalies of pulmonary veins. In our study, gradient-echo images were equal or superior to spin-echo images.

MR imaging of congenital anomalies of the thoracic veins.

Congenital anomalies of the thoracic veins are infrequent but important developmental abnormalities. Thoracic venous anomalies can be classified as systemic or pulmonary. Systemic venous anomalies are often incidental findings, whereas pulmonary venous anomalies are more likely to manifest with cyanosis and to be associated with congenital cardiac abnormalities, especially atrial septal defect. Magnetic resonance (MR) imaging provides excellent delineation of the abnormal vessels and associated cardiac defects. Conventional spin-echo (SE) techniques show blood flow as a signal void and are sufficient for demonstrating the aberrant venous anatomy in most cases. Gradient-echo images show flowing blood as high signal intensity and are useful for clarifying the course of anomalous veins when vessel walls are difficult to visualize on SE images. Phase-contrast images are valuable for ascertaining the direction of blood flow and thus provide a physiologic method of distinguishing the vertical vein of anomalous pulmonary venous return from a left superior vena cava. MR imaging is useful for delineating both the thoracic venous and accompanying intracardiac anomalies and is a valuable, complementary technique to echocardiography, angiography, and computed tomography in the evaluation of patients with these abnormalities.

The adenylate kinase genes of M. voltae, M. thermolithotrophicus, M. jannaschii, and M. igneus define a new family of adenylate kinases.

The adenylate kinase genes (adkA) were cloned from four closely related methanogenic members of the Archaea: the mesophile Methanococcus voltae (Mv), the thermophile M. thermolithotrophicus (Mt) and the hyperthermophiles M. jannaschii (Mj) and M. igneus (Mi). All four genes encode a protein of 192 amino acids (aa), and the four enzymes were closely related, with 68-81% aa identity in pairwise comparisons. It is anticipated that the enzyme set will provide the basis for studies that can establish the structural basis for ADK thermal stability. Mj and Mi contained a gene homologous to M. vannielii sec Y upstream of adkA, while Mv and Mt contained an unidentified, yet conserved, upstream open reading frame (ORF). Mt, Mj and Mi, but not Mv, contained an unidentified, yet highly conserved, ORF directly downstream of adkA. Based on their size, predicted secondary structure and phylogenetic relation to bacterial and eukaryotic adenylate kinases (ADK), it was concluded that the archaeal adkA genes encoded a unique class of ADK, and suggested that Euryarchaeotal and Crenarchaeotal branches of the Archaea contain separate subclasses of the enzyme.

Effect of computerized requisition of radiology examinations on the transmission of clinical information.

RATIONALE AND OBJECTIVES: The authors developed a method to evaluate the availability and accuracy of clinical data proffered by clinicians when ordering radiologic examinations with a computer order-entry system. METHODS: Two thousand consecutive clinical indications for a spectrum of pediatric imaging studies were scrutinized for accuracy by means of computerized chart review, verbal communication with clinical attending staff, and reference to surgical and laboratory results. The indications were classified as appropriate, incorrect, misleading, or incomplete. RESULTS: Of the 2,000 stated indications, 1,464 (73%) provided a reasonable, if minimal, amount of clinical information; however, in 376 (19%) cases the diagnosis or proximate indication was incorrect, in 108 (5%) cases the data were incomplete, and in 52 (3%) cases the information was misleading. CONCLUSION: Computer order-entry systems can improve the transmission of clinical information but they allow misinformation to be provided.

Thoracic disease in children with AIDS.

Knowledge of common and uncommon thoracic pathologic conditions in children with acquired immunodeficiency syndrome (AIDS) can expedite disease management. Chest radiography, computed tomography (CT), and magnetic resonance (MR) imaging are useful in cases involving possible complications of thoracic AIDS. Lymphocytic interstitial pneumonitis (LIP) is generally seen on plain radiographs and CT scans as a diffuse, symmetric, reticulonodular or nodular pattern, occasionally associated with mediastinal or hilar adenopathy. Chronic consolidations and bronchiectasis may be observed in pediatric AIDS patients with no evidence of previous LIP. Bacterial pneumonia, a frequent initial manifestation of AIDS, appears as lobar or segmental consolidations on radiographs. Radiographic findings of Pneumocystis carinii pneumonia, the most common infection, include rapidly progressive increased air-space opacity with air bronchograms. Lymphoma often appears as a mediastinal or hilar mass, often without involvement of the lung parenchyma. Thoracic smooth muscle tumors have also been observed in children with AIDS. Multilocular thymic cysts have low attenuation on CT scans and increased signal intensity on T2-weighted MR images. Most pediatric AIDS patients with cardiac disease have cardiomegaly, often associated with pulmonary edema, at chest radiography. An esophagogram may show ulceration, plaque formation, mucosal edema, and dysmotility in patients with candidal esophagitis.

Does growth hormone influence the severity of phosphopenic rickets?

The severity of bone disease in phosphopenic rickets is not correlated with serum phosphate levels. In order to determine whether growth hormone (GH) secretion may influence rachitic changes, we evaluated the 24 h integrated concentration of growth hormone (IC-GH) in five children with phosphopenic rickets. Two patients with marked clinical and roentgenographic rachitic abnormalities had normal IC-GH levels. In contrast, three patients with low IC-GH levels had mild rachitic changes. We suggest that the level of spontaneous GH secretion may be one factor which influences the severity of phosphopenic rickets.

Presternal soft tissue calcifications following mediastinal radiotherapy for Hodgkin's disease.

A patient is described in whom dense calcifications developed in the presternal soft tissues of the chest four years after mediastinal radiotherapy. This is believed to represent dystrophic calcification in previously normal but incidentally radiated tissues following standard dose radiotherapy to the mediastinum for stage IIA Hodgkin's disease.

Pneumopericardium as a complication of balloon atrial septostomy.

An infant with transposition of the great arteries and a coexistent pneumothorax, developed a pneumopericardium during balloon atrial septostomy.

Gray-scale (B-mode) sonography of the maxillary sinus.

Gray-scale sonographic examination of the maxillary sinuses of five normal volunteers and 12 patients with maxillary sinus disease was performed and correlated with other radiologic imaging modalities, clinical follow-up, and, in two cases, surgical findings. B-mode scanning is a rapid, potentially useful, nonionizing diagnostic modality for determining whether the maxillary sinuses contain fluid or are normally aerated. Sonography may also demonstrate mucosal thickening, focal soft tissue masses, and complex collections.

Ethiodized oil emulsion enhanced computerized tomography in the preoperative assessment of metastases to the liver from the colon and rectum.

Selective reticuloendothelial (RE) cell uptake of ethiodized oil emulsion 13 (EOE-13), an emulsion of Ethiodol (ethiodized oil) roentgenographic contrast material in a phosphate buffer, permits detection of small metastatic lesions of the liver and spleen through enhancement of roentgenographic density differences on computerized tomography (CT) between tissues containing and not containing RE cells. To determine the efficacy of this contrast material in the assessment of patients with metastatic disease of the liver, routine CT and emulsion enhanced tomography (EOE) were performed in a series of 15 patients prior to surgical exploration for treatment of carcinoma of the colon and rectum. All patients were suspected of harboring hepatic metastasis on the basis of clinical examination, liver function tests or radionuclide scans. EOE consistently demonstrated the nature and location of hepatic defects. Surgical exploration failed to locate one metastasis that was judged to be real because of progressive enlargement on EOE and CT over a period of two years. CT scans detected metastases in three patients subsequently shown to have normal livers and failed to detect disease in one patient subsequently shown to have metastases. EOE contrast material provides a more sensitive and accurate picture of metastatic liver involvement from carcinoma of the colon and rectum than is available on routine CT. The information provided by the results of this test can be useful in preoperative planning when treatment of disease of the liver is considerable feasible.

Imaging modalities of craniosynostosis with surgical and pathological correlation.

Premature fusion of the sutures of the skull has been extensively analyzed and several diagnostic imaging modalities have been proposed. Radiographic, scintigraphic and computed tomographic features of craniosynostosis have been reported. This study was initiated (a) to determine the value and accuracy of plain skull radiography, skull scintigraphy and cranial CT; and (b) to determine the optimal imaging modality for the evaluation of a clinically suspected craniosynostosis. The study is based on 36 patients with clinical suspicion of craniosynostosis who underwent craniectomy and cranioplasty. One hundred and three sutures were pathologically and/or surgically evaluated. The overall accuracy rate for skull radiography was 89%, skull scintigraphy, 66%, and cranial CT, 94%. Routine skull series are adequate in the majority of cases of craniosynostosis. Skull scintigraphy is less accurate, more costly, and has a limited role in the evaluation of craniosynostosis. Cranial CT should be reserved for those cases in which the findings in the routine skull series are not clearly positive or negative, or in cases of more complex craniofacial anomalies.

Radiographic findings in neonatal pneumonia.

The chest films of 30 infants with autopsy-proved pulmonary infections were reviewed to assess the radiographic changes in neonatal pneumonia. The most common abnormality identified was bilateral alveolar densities, noted in 77% of cases. One-third of patients had characteristically extensive, dense alveolar changes with numerous air bronchograms. A pattern of radiographic abnormalities consistent with transient tachypnea of the newborn was found in 17% of cases, and a second pattern resembling hyaline membrane disease was found in 13%. Recognition of the spectrum of expected radiographic changes can aid in the diagnosis of neonatal pneumonia, particularly if this information is correlated with the clinical features.

CT of benign cystic abdominal masses in children.

Computed tomography (CT) correctly portrayed the gross anatomic features of six mesenteric, omental, and ovarian cysts and diagnosed two pancreatic pseudocysts in children. Large, well defined, low-density masses were found, often containing septa and filling most of the abdomen and pelvis. CT displayed the size and extent of the mass and showed extrinsic compression or displacement of surrounding structures. Different pathologic entities may have similar CT appearances, particularly with very large cystic masses.