Hydration of an 18O epoxide by a cytosolic epoxide hydrolase from mouse liver

The mechanism of enzymatic epoxide hydration by a cytosolic or 100,000 g soluble mammalian liver enzyme (in contrast to the microsomal enzymes) was examined by monitoring ¹⁸O distribution following chemical and enzymatic hydrations of ¹⁶O or ¹⁸O epoxide labeled (±) 1-(4′-ethylphenoxy)-3, 7-dimethyl-6, 7-epoxyoctane. Acid catalyzed hydration of the ¹⁸O epoxide in ¹⁶O water, and hydration of the ¹⁶O epoxide in ¹⁸O water, indicated that attack by water was predominantly on the tertiary carbon (C-7). Enzymatic epoxide hydration led to attack predominantly on secondary carbon (C-6). These data are consistent with water attacking as a nucleophile in the enzymatic reaction.     

Plant tumor reversal associated with the loss of foreign DNA

Summary Transformation of plant tissues into crown gall tumors has been associated with the transfer of a portion of a tumor-inducing plasmid (Ti-plasmid) into plant DNA. Various laboratories have regenerated normal-appearing plants from a number of crown gall tumors. This study investigates the fate of the foreign DNA in a series of tissues derived from various parts of a plant regenerated from the tumor BT-37 by Braun and his coworkers. It was found that all the foreign DNA sequences were lost from tissues that had lost all their tumorous traits; whereas the plasmid DNA sequences were still present in tissues that appeared normal but still exhibited tumorous traits when returned to tissue culture media. From these studies it would appear that the presence of the Ti-plasmid sequences in the plant DNA is required for the maintenance of the transformed state. Presented in the Symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA 26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society.     

Synthesis of membrane glycoproteins in rat small-intestinal villus cells. Redistribution of l-[1,5,6-3H]-fucose-labelled membrane glycoproteins among Golgi, lateral basal and microvillus membranes in vivo

The biogenesis of plasmalemma glycoproteins of rat small-intestinal villus cells was studied by following the incorporation of l-[1,5,6-(3)H]fucose, given intraperitoneally with and without chase, into Golgi, lateral basal and microvillus membranes. Each membrane fraction showed distinct kinetics of incorporation of labelled fucose and was differently affected by the chase, which produced a much greater decrease in incorporation of label into Golgi and microvillus than into lateral basal membranes. The kinetic data suggest a redistribution of newly synthesized glycoproteins from the site of fucosylation, the Golgi complex, directly into both lateral basal and microvillus membranes. The observed biphasic pattern of label incorporation into the microvillus membrane fraction may be evidence for a second indirect route of incorporation. The selective effect of the chase suggests the presence of two different pools of radioactive fucose in the Golgi complex that differ in (1) their accessibility to dilution with non-radioactive fucose, and (2) their utilization for the biosynthesis of membrane glycoproteins subsequently destined for either the microvillus or the lateral basal parts of the plasmalemma. The radioactively labelled glycoproteins of the different membrane fractions were separated by sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis and identified by fluorography. The patterns of labelled glycoproteins in Golgi and lateral basal membranes were identical at all times. At least 14 bands could be identified shortly after radioactive-fucose injection. Most seemed to disappear at later times, although one of them, which was never observed in microvillus membranes, increased in relative intensity. All but two of the labelled glycoproteins present in the microvillus membrane corresponded to those observed in Golgi and lateral basal membranes shortly after fucose injection. The patterns of labelled glycoproteins in all membrane fractions were little affected by the chase. These data support a flow concept for the insertion of most surface-membrane glycoproteins of the intestinal villus cells.     

T cell induction of precursor B cells: Temporal separation of helper T cell functional activities

Summary The temporal relationships involved in T cell induction of immunoglobulin-secreting B cells have been studied by employing a pulse label technique, in vitro. It was shown that addition of rabbit thymocytes or splenic T cells to B cell-enriched splenocyte populations at the time of initiation of cultures resulted in a marked enhancement in induction of immunoglobulin-secreting cells. However, even a two-hour delay in the addition of thymus cells was sufficient to reduce substantially the extent of induction when measured 70 hours later. Besides this early requirement for thymocytes, a late requirement was also detectable. Thus, thymus cells and splenocyte populations upon being mixed, subsequent to being cultured separately for 72 hours, yielded a several-fold enhancement in [³H]-immunoglobulin secreted during the course of a 90-minute labeling period with [³H]-leucine. Moreover, both the early and late thymocyte effects were lost after treatment with anti-thymocyte serum and complement.The thymocyte-mediated enhancement of immunoglobulin secretion by splenocytes that occurs late in the induction process was detected with spleen cells cultured for two or three days but not with freshly-isolated splenocytes. Although the rate of appearance of extracellular immunoglobulins was markedly enhanced by fresh thymus cells, the rate of appearance of intracellular immunoglobulins in such spleen cells was unchanged. The secretion-stimulating (secretagogue) activity of thymocytes appeared to be specific in that thymus cells were without effect on the rate of secretion of serum albumin by liver cells.In regard to the induction of immunoglobulin-secreting cells, both B and T cell-enriched population's were sensitive to mitomycin C treatment performed before initiation of cell culture, indicating that not only B cells but also T cells undergo some form of differentiation or maturation prior to functioning in the induction of immunoglobulin-producing cells. It should be noted in this context that the late T cell requirement was unaffected by prior mitomycin C treatment of thymocytes. On the other hand, thymocytes heated at 60°C for 5 minutes did not enhance immunoglobulin secretion when added at any time and the late thymocyte requirement could not be replaced with medium in which thymocytes had been previously cultured.     

Einige endokrinologische Besonderheiten der V?gel

Zusammenfassung Anhand neuer embryologischer, morphologischer, physiologischer und biochemischer Befunde werden die vogelspezifischen Eigentümlichkeiten von drei endokrinen Systemen diskutiert: Pinealkomplex, hypothalamo-hypophysäres System und gastrointestinales Endokrinium.Trotz der allgemein besonders starken Beeinflußbarkeit der Vögel durch photoperiodische Veränderungen ist bei ihnen der Pinealkomplex zu einer intracranialen endokrinen Drüse reduziert. Diese Epiphyse (Pinealorgan) zeigt unter experimentellen Bedingungen eine außerordentliche Unabhängigkeit von photoperiodischer Steuerung. Das völlige Fehlen des Pinealkomplexes bei den relativ nahe verwandten Krokodilen deutet auf die Möglichkeit hin, daß dies wohl eher phylogenetisch als funktionell zu erklären ist.Das hypothalamo-hypophysäre System ist im wesentlichen reptilienartig, zeigt aber drei auffallende Spezialisierungen: 1. Eine hochentwickelte Eminentia mediana, welche aus zwei getrennten Regionen besteht. 2. Die Pars distalis ist mit der Eminentia so verbunden, daß ihre beiden Unterabteilungen (cephaler und caudaler Lappen) von beiden Regionen der Eminentia über getrennte Portalgefäße versorgt werden. 3. Den Vögeln als Gruppe fehlt die Pars intermedia.Die auffallendsten Besonderheiten des gastrointestinalen Endokriniums stehen mit dem Inselorgan in Verbindung: insulinproduzierende B-Zellen und glukagonbildende A-Zellen sind weitgehend in besondere Inseln getrennt. Im Gegensatz zu dem der anderen Tetrapoden ist das Fettgewebe der Vögel insulin-unempfindlich. Die endokrine Kontrolle des Fettgewebes erfolgt über eine indirekte anabole Route (durch prolaktinstimulierte Lipogenese in der Leber) sowie eine direkte katabole Route durch Pankreasglukagon.Bei einem Vergleich mit anderen Gnathostomengruppen zeigen Epiphyse, Adenohypophyse und Inselorgan einen besonders starken Trend zur Unabhängigkeit von direkter Innervation. In bezug auf Adenohypophyse und Inselorgan repräsentieren dabei die Vögel das entgegengesetzte Extrem zu den Knochenfischen (Teleostier), bei denen diese Drüsen besonders stark innerviert sind.Die Vögel und Teleostier werden kurz mit den Myxiniden verglichen, deren endokrines System besonders schwach entwickelt ist. Die Unterschiede zwischen den drei Gruppen werden durch drei verschiedene Wege der Anpassung an Umweltbedingungen gedeutet: 1. Aktive Anpassung durch ein hochentwickeltes neuro-endokrines Kontrollsystem (Teleostier). 2. Passive, osmokonforme Anpassung, welche ein stark entwickeltes Endokrinium überflüssig macht (Myxiniden). 3. Vermeidung ungünstiger Umweltbedingungen durch Flugvermögen; eine verfeinerte, sekretomotorische Kontrolle der endokrinen Drüsen des normalen Stoffwechsels ist unnötig (Vögel).

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Some endocrine specializations of the birds

Summary Against the background of recent embryological, morphological, physiological and biochemical studies, peculiarities of three different avian endocrine systems are discussed: pineal complex, hypothalamo-hypophysial system, and gastrointestinal endocrine system.Despite the marked photosensitivity of the birds in general, their pineal complex is reduced to an intracranial pineal gland, which shows a very high degree of functional autonomy when released from photoperiodic control. The complete absence of the pineal complex in the alligators suggests that this may be due to phylogenetic rather than adaptive reasons.The hypothalamo-hypophysial system is basically of reptilian type, but shows three marked specializations: (1) the highly developed median eminence consists of two distinct regions; (2) the Pars distalis is located so, that both of its subdivisions (cephalic and caudal lobe) appear to receive distinctly separate vascularisation from the median eminence; (3) the birds as a group lack a Pars intermedia.Within the gastrointestinal endocrine system of birds, the most obvious peculiarities identified so far are connected with the islet organ: insulin-producing B-cells and glucagonproducing A-cells are largely separated in different islets, and contrary to the situation in other tetrapodes, the avian adipose tissue is insulin-insensitive. The endocrine control of the adipose tissue involves an indirect anabolic route via prolactin-induced hepatic lipogenesis, and a direct catabolic route, via pancreatic glucagon.When compared with other groups of gnathostomes, the pineal gland, adenohypophysis and islet organ of the birds show a particularly strong trend towards independence from secretomotor innervation. With respect to the adenohypophysial and islet innervation, the birds represent the opposite extreme to the teleosts, whose adenohypophysis and islet organ are particularly well innervated.Birds and teleosts are compared with the Myxinidae, whose endocrine system is particularly poorly developed. It is hypothesized that the differences between the endocrine systems of these three groups reflect three different ways of adjustment to environmental conditions: (1) teleosts actively adjust to a continuous challenge from external osmolarity, whose control has to be integrated with the milieu interne and nutritional factors. They developed a highly sophisticated control system of their endocrines, which is capable of overriding humoral stimuli by nervous interference. (2) The Myxinidae passively conform with the osmotic environment, which makes a highly developed endocrine control system unnecessary. (3) The birds are shielded from environmental factors by a specialized body surface, and they can easily avoid unfavorable conditions by flight. This makes a sophisticated and fast acting (i.e. nervous) control of such endocrines unnecessary, which are involved in the maintenance of the normal milieu interne.Wir danken MissKathleen Matt für die Hilfe bei der Anfertigung der Zeichnungen.

     

Addition of Nitrogen Increases Variability of Vegetation Cover in an Arid System with Unpredictable Rainfall

Ecosystems - Addition of nitrogen (N) to rangeland that has been degraded through overgrazing or drought can hasten vegetation recovery. Additional N may influence temporal stability of vegetation...