Structural studies of hydroxycitrates and their relevance to certain enzymatic mechanisms.

The crystal structures of the ethylenediamine salts of two diastereoisomeric hydroxycitratesy are described, and their conformations in the solid state are analyzed. In both structures, the HOCCOH torsion angle is approximately 60 ° as found for many tartrates and mesotartrates. The presence of three carboxyl groups and two hydroxyl groups in hydroxycitrates leads to 10 possible types of tridentate metal chelates. Since bacterial citrate lyase and ATP citrate lyase require metal ions, the possible geometries of hydroxycitrate chelation have been compared with those of citrate, and as a result, some information on the geometry of each enzymic active site has been obtained. If the hydroxycitrate binds in the same manner as citrate, the C(3)&;z.sbnd;C(4) bond will be in the correct position to be cleaved. Other modes of binding of hydroxycitrate, if they can be accommodated in the active site of the enzyme, are nonproductive and compete with the citrate-like mode causing inhibition. It is possible, in these alternate modes of binding of hydroxycitrates, for additional binding to side chains in the active site of the enzyme to occur, resulting in extremely potent inhibition.     

Urethral plugs and urine retention in male mice

Because MM male mice suffer from a high incidence of urinary tract infection, an assessment was made as to whether the urethral plugs, which occur in male rodents, might be involved in its aetiology. When killed, males more commonly retained urine in their bladders than females but there was no significant difference between strains or method of killing. Males also voided urine more often during stressful handling followed by abdominal pressure, but also retained some urine more often than females. The study of sexually immature mice demonstrated no sex differences and no urine was retained in any bladder. It was concluded that the high frequency of urine retention in mature males is attributable to the presence of urethral plugs but these could not be implicated in the cause of MM urinary tract infection because of comparable findings in the controls. However, the possibility was considered that the plugs might facilitate infection of the kidneys once a bladder infection had become established.     

Free radicals: basic concepts concerning their chemistry, pathophysiology, and relevance to plastic surgery

This paper is an attempt to present important concerns in the rapidly expanding field of free radicals to a plastic surgical audience. Mechanisms and a systematic approach to free-radical pathology are presented, with several illustrative areas discussed more deeply.     

New actions of melatonin and their relevance to biometeorology

 Melatonin is not only produced by the pineal gland, retina and parietal but also by various other tissues and cells from vertebrates, invertebrates, fungi, plants, multicellular algae and by unicells. In plants, many invertebrates and unicells, its concentration often exceeds that found in vertebrate blood by several orders of magnitude. The action of melatonin is highly pleiotropic. It involves firstly, direct effects, via specific binding sites in various peripheral tissues and cells of vertebrates, including immunomodulation; secondly, systemic influences on the cytoskeleton and nitric oxide formation, mediated by calmodulin; and thirdly, antioxidative protection, perhaps also in the context of photoprotection in plants and unicells. In some dinoflagellates, melatonin conveys temperature signals. On the basis of these comparisons, melatonin appears to mediate and modulate influences from several major environmental factors, such as the photoperiod, radiation intensity and temperature. Received: 18 March 1997 / Accepted: 16 July 1997     

Host factors and their relevance to virus infection in plants

Virus infection is established when viral proteins can interact with host factors to execute replication and/or cell-to-cell movement. Even after the virus infection has started, host resistance reactions, if trigged, would suppress further virus propagation. We would like to introduce what we understand about host factors as determinants of infection establishment and as key resistance molecules. Genome-wide information of Arabidopsis is providing us much information about such host factors involved in virus infection.     

Substratum-induced morphological changes in a marine bacterium and their relevance to biofilm structure.

The effects of surfaces on the physiology of bacteria adhering to surfaces or immobilized within biofilms are receiving more interest. A study of the effects of hydrophobic and hydrophilic substrata on the colonization behavior of a marine bacterium, SW5, revealed major differences in the morphology of SW5 on these surfaces. Using epifluorescence, scanning confocal laser, and on-line visualization (time-lapse video) microscopy, the organisms at hydrophobic surfaces were characterized by the formation of tightly packed biofilms, consisting of single and paired cells, whereas those at hydrophilic surfaces exhibited sparse colonization and the formation of chains more than 100 microns long, anchored at the surface by the terminal (colonizing) cell. The results are discussed in terms of the possible factors inducing the observed morphological differences and the significance of these differences in terms of biofilm structure and plasmid transfer when SW5 is the recipient organism.     

Plasma ferritin concentrations: their clinical significance and relevance to patient care.

In healthy persons the plasma ferritin concentration is a sensitive index of the size of body iron stores. It has been successfully applied to large-scale surveys of the iron status of populations. It has also proved useful in the assessment of clinical disorders of iron metabolism. A low plasma ferritin level has a high predictive value for the diagnosis of uncomplicated iron deficiency anemia. It is of less value, however, in anemia associated with infection, chronic inflammatory disorders, liver disease and malignant hematologic diseases, for which a low level indicates iron deficiency and a high level excludes it, but intermediate levels are not diagnostic. Measuring the plasma ferritin concentration is also useful for the detection of excess body iron, particularly in idiopathic hemochromatosis, but again it lacks specificity in the presence of active hepatocellular disease. If iron overload is suspected in these circumstances determination of the iron content of a percutaneous liver biopsy specimen is required. In families with idiopathic hemochromatosis the combined determination of the plasma ferritin concentration and the transferrin saturation is a sufficient screen to identify affected relatives; however, estimation of the hepatic iron concentration is required to establish the diagnosis.     

Several cranial indices and their relevance to fossil man

An evaluation of three cranial indices proposed by Le Gros Clark ('50) is presented in light of hominid fossil material not previously considered. The data analysis suggests that the supra-orbital height index is an important contribution to cranial analysis and elaborations of it may prove valuable. From the results, the authors suggest that the two australopithecine types be separated on the genus level, i.e., Australopithecus africanus and Paranthropus robustus. It is also proposed that Skhūl V be considered Homo sapiens sapiens. The authors generally conclude that a more dynamic approach in primate cranial analysis is needed. This approach should incorporate non-morphological variables.     

牙斑幽门螺杆菌与慢性胃炎之间的关系

目的研究牙斑幽门螺杆菌与慢性胃炎之间的关系。方法对胃炎组、胃炎治疗组分别进行牙斑和胃黏膜幽门螺杆菌培养和比较。结果牙斑细菌培养：胃炎组阳性14例,阳性率为12．8％;治疗组阳性11例,阳性率为10．1％。胃黏膜细菌培养：胃炎组阳性47例,阳性率为43．1％;治疗组阳性19例,阳性率为17．4％。治疗前后比较牙斑标本差异无显著性（P〉0．05）,胃黏膜标本差异有非常显著性（P〈0．001）。结论牙斑中确实存在着幽门螺杆菌,而且是胃内反复感染的源泉,以致慢性胃病反复发作,难以治愈。     

Biosynthesis and inactivation of endocannabinoids: relevance to their proposed role as neuromodulators.

The two putative endogenous ligands of cannabinoid receptors, anandamide and 2-arachidonoylglycerol, are synthesized by and released from neurons in a Ca2+-dependent fashion, and re-uptaken and catabolized by both neurons and astrocytes. These biochemical features of the endocannabinoids, as well as some of their pharmacological effects in both central and peripheral nervous systems, suggest a role as neuromodulators for these metabolites. This neuromodulatory role is supported by the brain regional distribution of anandamide, its biosynthetic precursor and its major inactivating enzyme, and by the existence of possible regulatory mechanisms for the biosynthesis and inactivation of endocannabinoids, which are reviewed in this article.     

Cellular mechanisms of brain energy metabolism and their relevance to functional brain imaging.

Despite striking advances in functional brain imaging, the cellular and molecular mechanisms that underlie the signals detected by these techniques are still largely unknown. The basic physiological principle of functional imaging is represented by the tight coupling existing between neuronal activity and the associated local increase in both blood flow and energy metabolism. Positron emission tomography (PET) signals detect blood flow, oxygen consumption and glucose use associated with neuronal activity; the degree of blood oxygenation is currently thought to contribute to the signal detected with functional magnetic resonance imaging, while magnetic resonance spectroscopy (MRS) identifies the spatio-temporal pattern of the activity-dependent appearance of certain metabolic intermediates such as glucose or lactate. Recent studies, including those of neurotransmitter-regulated metabolic fluxes in purified preparations and analyses of the cellular localization of enzymes and transporters involved in energy metabolism, as well as in vivo microdialysis and MRS approaches have identified the neurotransmitter glutamate and astrocytes, a specific type of glial cell, as pivotal elements in the coupling of synaptic activity with energy metabolism. Astrocytes are ideally positioned to sense increases in synaptic activity and to couple them with energy metabolism. Indeed they possess specialized processes that cover the surface of intraparenchymal capillaries, suggesting that astrocytes may be a likely site of prevalent glucose uptake. Other astrocyte processes are wrapped around synaptic contacts which possess receptors and reuptake sites for neurotransmitters. Glutamate stimulates glucose uptake into astrocytes. This effect is mediated by specific glutamate transporters present on these cells. The activity of these transporters, which is tightly coupled to the synaptic release of glutamate and operates the clearance of glutamate from the extracellular space, is driven by the electrochemical gradient of Na+. This Na(+)-dependent uptake of glutamate into astrocytes triggers a cascade of molecular events involving the Na+/K(+)-ATPase leading to the glycolytic processing of glucose and the release of lactate by astrocytes. The stoichiometry of this process is such that for one glutamate molecule taken up with three Na+ ions, one glucose molecule enters an astrocyte, two ATP molecules are produced through aerobic glycolysis and two lactate molecules are released. Within the astrocyte, one ATP molecule fuels one 'turn of the pump' while the other provides the energy needed to convert glutamate to glutamine by glutamine synthase. Evidence has been accumulated from structural as well as functional studies indicating that, under aerobic conditions, lactate may be the preferred energy substrate of activated neurons. Indeed, in the presence of oxygen, lactate is converted to pyruvate, which can be processed through the tricarboxylic acid cycle and the associated oxidative phosphorylation, to yield 17 ATP molecules per lactate molecule. These data suggest that during activation the brain may transiently resort to aerobic glycolysis occurring in astrocytes, followed by the oxidation of lactate by neurons. The proposed model provides a direct mechanism to couple synaptic activity with glucose use and is consistent with the notion that the signals detected during physiological activation with 18F-deoxyglucose (DG)-PET may reflect predominantly uptake of the tracer into astrocytes. This conclusion does not question the validity of the 2-DG-based techniques, rather it provides a cellular and molecular basis for these functional brain imaging techniques.     

Properties of DNA rosettes and their relevance to chromosome structure

We have studied the spreading conditions that lead to the formation of rosettes in DNA and chromatin preparations from the amphibians Bufo marinus and Bolitoglossa subpalmata and the bacterium Shigella. Both nuclear preparations and extensively deproteinized DNA produced rosettes. The longest fibers and the most symmetric rosettes were observed in amphibian nuclear spreadings. In this procedure purified nuclei were submitted immediately to Kleinschmidt spreading over various types of hypophase. Distilled-water hypophases were most conducive for rosette production or stability. Rosettes were observed with cytochrome C as the basic protein, but not with ribonuclease A and bovine serum albumin. We cannot prove that all rosettes are artifacts of the spreading procedure, but we believe that at least some result from the expansion of compact DNA doughnuts and other structures that are apparently formed in the presence of basic proteins in salt concentrations over 40 mM (Olins and Olins 1971; Manning 1979). The dilute hypophase requirement is explainable by the assumption that dilution and spreading effects unfold a compact precursor. Occasionally we have detected structures that appear to be intermediates in the process of doughnut unfolding and that illustrate a procedure that may give rise to rosettes.