Elektron-Spin-Resonanz-Untersuchungen der Reaktionskinetik strahleninduzierter freier Radikale des Cholesterins

Zusammenfassung Die Reaktionskinetik strahleninduzierter freier Radikale des Cholesterins wurde in flüssiger Phase bei Raumtemperatur mittels ESR-Spektroskopie untersucht. Mit Hilfe eines geeigneten photochemischen Initiationssystems ließen sich in Cyclohexanlösung unter UV-Bestrahlung (235 nm265 nm) genau dieselben freien Radikale des Cholesterins darstellen, die schon früher [9, 7] in röntgenbestrahltem Cholesterinpulver beobachtet worden waren. Bei ausreichendem O₂-Partialdruck (3·10⁴Torr) über der Probenlösung trat das ESR-Spektrum eines Peroxyradikals auf, das mittels der Analyse seiner Reaktionsprodukte (7-Hydroxy-Cholesterin und 7-Keto-Cholesterin) mit dem Cholesteryl-7-peroxyradikal identifiziert wurde. Die Kinetik sowohl der Bildung als auch des Zerfalls des Radikals entsprachen einer Reaktion von 2. Ordnung. Die Geschwindigkeitskonstante für den bimolekularen Zerfall, eine Disproportionierung in Alkohol und Keton unter Abgabe eines Moleküls O₂, wurde bei Raumtemperatur zuk ₂=(1,8 _–0,6 ^+0,9 )·10⁶ sec^–1M^–1·l bestimmt. Ferner wurde gezeigt, daß das Cholesteryl-7-peroxyradikal aus dem freien Radikal Cholesteryl-7 durch Anlagerung eines Moleküls O₂ entsteht. Für die Geschwindigkeitskonstante dieser Reaktion ergab sich eine untere Schranke vonk ₁=0,40·10¹⁰ sec^–1M^–1·l.

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Electron spin resonance investigations on radiation-induced free radicals of cholesterol in liquid phase

Summary The reaction kinetics of radiation-induced free radicals of cholesterol was studied in liquid phase at room temperature by means of e.s.r. spectroscopy on a solution of cholesterol in cyclohexane. Using a convenient photochemical initiation system, just those free radicals of cholesterol could be generated by the filtered u.v. radiation from a Xe high pressure lamp (235 nm265 nm) as were observed already a decade ago by Gordy [9] and by Ehrenberg, Löfroth [7] in X-irradiated cholesterol powder. At sufficiently high O₂-pressures (3·10^–4 Torr) over the sample solution a peroxy radical e.s.r. spectrum arose during u.v. irradiation which was identified by product analysis (7-hydroxy-cholesterol and 7-keto-cholesterol) to be dueto a cholesteryl-7-peroxyradical. The radical'sgeneration and decay kinetics was governed by a second order reaction. The velocity constant for bimolecular decay of the cholesteryl-7-peroxyradical was found to be k₂=(1.8 _–0,6 ^+0,9 )·10⁶sec^–1M^–1·l at room temperature. Furthermore it could be shown that the cholesteryl-7-peroxyradical was built up by the addition of one molecule of O₂ to a cholesteryl-7 free radical. For this reaction a value ofk ₁=0.4·10¹⁰ sec^–1 M^–1·l was estimated as a lower limit of the velocity constant.

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Die Arbeit stellt einen Auszug aus einer Dissertation an der Technischen Hochschule München dar.     

CHROMOSOME NUMBERS IN COMPOSITAE V. ASTEREAE II.

Reports of 100 new chromosome counts are made for the tribe Astereae of Compositae, mostly based on determinations of meiotic material, including first counts for 9 genera and 53 species. Counts are now available for 58 of the approximately 100–120 genera and 431 of the approximately 2000 species in the tribe. Comparisons are made between chromosome number and habit and also between chromosome number and geographical distribution. Species and genera with a basic number of x = 9 are the most abundant. Within different phyletic lines x = 9 is also the most abundant number. On the other hand, many species with x = 4 and 5, belonging to a number of small, largely annual genera, are concentrated in southwestern North America. The low chromosome number in these plants is probably correlated with the dry habitat they occupy, and is most likely a specialized condition.     

Kurze Mitteilungen

Ohne Zusammenfassung     

Growth and reproduction as a function of temperature and salinity inClava multicornis (Cnidaria,Hydrozoa)

Summary 1. Rates of growth (length increase of stolons) and of asexual reproduction (increase in number of polyps) were determined in secondaryClava multicornis colonies of a clone exposed to 12 different combinations of water temperature and salinity (12°, 17°, 22° C; 16 , 24 , 32 , 40 S). Sexual reproduction (via gonophores) has been observed only at 12° and 17° C; temperature and salinity ranges are narrower for sexual than for asexual reproduction.2. The data obtained are insufficient for a detailed analysis; they provide, however, interesting insights into the variability of growth and reproduction ofC. multicornis caused by different intensities of temperature and salinity.3. It appears that temperature requirements for maximum colony increase are reduced as the colony grows older.4. One feeding period per 24 hours seems insufficient for maximum growth and reproduction at the higher temperature levels, especially at 22° C.5. The different degrees of environmental stress endured during the initial period of transfer into the test combinations of temperature and salinity have affected the resulting colony size at least up to an age of 39 days. More appropriate criteria for assessment of rates of growth and reproduction are therefore the doubling times (number of days within which stolon length and polyp numbers taken 20 days after initiation of experiments have doubled).6. On the basis of doubling time values, increase in stolon length is progressively reduced with increasing water temperature (12°, 17°, 22° C). At 12° and 17° C stolons grow fastest in 32 , followed by 24 , 16 and 40 S; at 22° C stolon growth rates are identical in 32 and 24 S.7. Doubling times of polyp numbers per colony show a less obvious trend. In 56-day-old colonies, however, stolon length and polyp number are modified to similar degrees by the various temperatures and salinities offered. The sequence of temperatures causing fastest increase in polyp number is 12°>17°>22° C; the respective sequence of salinities reads: 24 , 32 , 16 , 40 S.8. Stolon length and polyp number per colony increase exponentially; most curves obtained exhibit undulations indicating endogenous growth rhythms.9. During the initial period of transfer into the final test media, asexual reproduction via budding seems to have been stimulated by a reduction in salinity.10. The doubling times obtained forC. multicornis are considerably longer than those found forCordylophora caspia and indicate that our culture conditions may have been suboptimal.

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Wachstum und Reproduktion als Funktion von Temperatur und Salzgehalt beiClava multicornis (Cnidaria, Hydrozoa)

Kurzfassung Einzelpolypen eines Klons vonC. multicornis Forskål wurden schrittweise in 12 verschiedene Temperatur-Salzgehalts-Kombinationen überführt und — während sie zu neuen Kolonien heranwuchsen — das Längenwachstum ihrer Stolonen, die Geschwindigkeit ihrer asexuellen Vermehrung durch Knospung neuer Hydranthen sowie die Gonophorenausbildung (sexuelle Fortpflanzung) registriert. Die erhaltenen Daten sind unzureichend für eine detaillierte Analyse, gewähren jedoch interessante Einblicke in die Bedeutung der verschiedenen Temperatur- und Salzgehaltsbedingungen für Wachstum und Vermehrung. Die anfängliche, schrittweise Überführung in die Testmedien verursacht per se Leistungsunterschiede, deren Auswirkungen sich mindestens bis zu einem Alter von 39 Tagen verfolgen lassen. Doubling times stellen daher objektivere Kriterien dar als absolute Zuwachswerte. Die doubling times von Kolonien, welche länger als 20 Tage in den Testmedien gewachsen waren, zeigen eine Verringerung der Stolonenzuwachsrate mit steigender Temperatur (12°, 17°, 22° C). Die Reihenfolge der fördernden Wirkung der einzelnen Salzgehaltsstufen ergibt sich zu 32 , 24 , 16 , 40 S. Im Prinzip ähnliche Verhältnisse liegen hinsichtlich der asexuellen Vermehrungsrate vor. Bemessen an den getesteten Kriterien scheinen die Temperaturansprüche mit zunehmendem Koloniealter abzunehmen. Die errechneten doubling times sind wesentlich länger als beiCordylophora; möglicherweise deutet dieser Unterschied auf inadäquate Kulturbedingungen (Fütterung, Wasserbewegung) hin.

     

Carbon catabolite regulation of rebeccamycin production inSaccharothrix aerocolonigenes

Summary A new antitumor antibiotic named rebeccamycin was isolated from fermentations of an actinomycete,Saccharothrix aerocolonigenes. A defined medium was developed to study the regulation of synthesis of rebeccamycin byS. aerocolonigenes. In glucose medium formation of rebeccamycin was detected only after glucose was depleted. Examination of eleven different carbon sources revealed that carbon catabolite regulation is a major control mechanism for rebeccamycin production.     

Concerted generation of Ig isotype diversity in human fetal bone marrow

The human fetal bone marrow B cell compartment of 14- to 21-wk gestational age was examined phenotypically and with respect to Ig H chain commitment and diversity. A dramatic expansion of fetal marrow B cell pools at 16- to 18-wk gestational age characterizes a rapid and concerted chain of differentiation events. Transiently up to 1/4 of nucleated marrow cells are CD20+/CD21+ cells which begin to express surface Ig other than IgM. Limiting dilution analysis of EBV-infected marrow cells delineated a virtually exclusive commitment to IgM production until 15 wk and the absolute and relative number of these cells were small (approximately 5% of comparable adult values). In parallel to the rapid increase in total B cell pools size, cells committed and able to secrete any of the five Ig isotypes are generated by 16-wk gestational age and by 18 wk the frequencies of these cells rapidly reach levels typical for adult peripheral tissue such as blood or lymph node. Fetal L chain diversity always anticipated that observed in adult serum. In addition to rising pool sizes and diverse IgH expression, EBV transformability is a major variable during this period of B cell development with up to 2/3 of B lineage cells transformable, about half of which are pre-B cells. By 21-wk gestational age transformable pre-B cells have disappeared and (as in adult tissue) approximately 10 to 20% of CD20+ cells are transformable. The rapid, concerted expression of full H chain diversity during a narrow period in fetal development is unique to marrow and implies a lymphopoietic process in a privileged site rather than an immunologic differentiation event. During this event, the relative proportions between the different IgH classes expressed, resembled that found in adult tissue, perhaps suggesting that B cell inherent programming rather than only antigenic forces determine heavy chain choice. The staggered expression, early in postnatal life, of IgH regions 3' of the C mu locus may reflect regulatory functions rather than inherent immaturity of the B lineage.     

Responses and song pattern copying of Omega-type I-neurons in the cricket,Gryllus bimaculatus,at different prothoracic temperatures

Summary Omega-type I-neurons (ON/1) (Fig. 1A) were recorded intracellularly with the prothoracic ganglion kept at temperatures of either 8–9°, or 20–22° or 30–33 °C and the forelegs with the tympanal organs kept at ambient temperature (20–22 °C). The neurons were stimulated with synthetic calling songs (5 kHz carrier frequency) with syllable periods (SP in ms) varying between 20 and 100, presented at sound intensities between 40 and 80 dB SPL. The amplitude and duration of spikes as well as response latency decreased at higher temperatures (Figs. 1 B, 2, 6). At lower prothoracic temperatures (8–9 °C) the neuron's responses to songs with short SP (20 ms) failed to copy single syllables, or with moderate SP (40 ms) copied the syllable with low signal to noise ratio (Fig. 3). The auditory threshold of the ON/1 type neuron, when tested with the song model, was temperature-dependent. At 9° and 20 °C it was between 40 and 50 dB SPL and at 33 °C it was less than 40 dB SPL (Fig. 4). For each SP, the slope of the intensity-response function was positively correlated with temperature, however, at low prothoracic temperatures the slope was lower for songs with shorter SPs (Fig. 5). The poor copying of the syllabic structure of the songs with short SPs at low prothoracic temperatures finds a behavioral correlate because females when tested for phonotaxis on a walking compensator responded best to songs with longer SPs at a similar temperature.Abbreviations epsps excitatory postsynaptic potentials - ON/1 omega-type I-neuron - SP syllable period - SPL sound pressure level