Dark starvation and chloroplast function

Summary Mature spinach plants were held in the dark for several days. The photochemical activities and the activity of some enzymes related to NADP reduction were follwed in the chloroplasts isolated from leaves after dark starvation. Photosystem-II, measured by reduction of DPIP, remained stable during 6 days of darkening. The decrease of NADP reduction which appeared after 2 days of starvation was found to be due to protein autolysis rather than inactivation of the photosystems. The stability of photosystem-I was demonstrated by reactivation of NADP reduction after addition of purified ferredoxin and ferredoxin-NADP-reductase. After 4 days of starvation the restoration of the NADP reduction required in addition another, low-molecular-weight factor. From the isolation procedure and from its properties this factor is assumed to be identical with FRS. However, even in the presence of FRS only half of the total activity is restored after 7 days. The activity of the NADP-reducing system is restored in vivo when plants kept for 7 days in the dark are again illuminated.Abbreviations NADP nicotinamide-adenine-dinucleotide phosphate - DPIP 2,6-dichlorophenolindophenol - DCMU (3,4-dichlorophenyl)-1,1-dimethylurea - FRS ferredoxin-reducing-substance     

The product of the hypB gene, which is required for nickel incorporation into hydrogenases, is a novel guanine nucleotide-binding protein.

The products of the hyp operon genes are essential for the formation of catalytically active hydrogenases in Escherichia coli. At least one of these auxiliary proteins, HYPB, appears to be involved in nickel liganding to the hydrogenase apoprotein, since mutations in hypB can be phenotypically suppressed by high nickel concentrations in the medium (R. Waugh and D. H. Boxer, Biochimie 68:157-166, 1986). To approach the identification of the specific function of HYPB, we overexpressed the hypB gene and purified and characterized the gene product. HYPB is a homodimer of 31.6-kDa subunits, and it binds guanine nucleotides, with a Kd for GDP of 1.2 microM. The protein displays a low level of GTPase activity, with a kcat of 0.17 min-1. The apparent Km for GTP, as measured in the GTP hydrolysis reaction, was determined to be 4 microM. A chromatography system was established to measure nickel insertion into hydrogenase 3 from E. coli and to determine the effects of lesions in hypB. Nickel appears to be associated only with the processed large subunit of hydrogenase 3 in the wild type, and hypB mutants accumulate the precursor form of this subunit, which is devoid of nickel. The results are discussed in terms of a model in which HYPB is involved in nickel donation to the hydrogenase apoprotein and in which GTP hydrolysis is thought to reverse the interaction between either HYPB or another nickel-binding protein and the hydrogenase apoprotein after the nickel has been released.     

Mechanisms underlying induced autoresuscitation failure in BALB/c and SWR mice.

Mechanisms underlying failure of autoresuscitation from hypoxic apnea were investigated. Failure was induced by repeated exposure to hypoxia. The influence of maturation was studied in adults, weanlings, and 10- and 5-day-old mice. Mice successful at autoresuscitation (BALB/c) as well as those prone to autoresuscitation failure (SWR weanlings) were studied. Hypoxic apnea was induced with 97% N2-3% CO2, and 21% O2 was given at its onset; electrocardiogram and ventilation were recorded. Hypoxic exposure was repeated if autoresuscitation (recovery of eupnea) occurred. Autoresuscitation failure (death) was induced in all mice. Young BALB/c mice tolerated more trials than older mice. SWR weanlings frequently failed to autoresuscitate on the initial exposure and tolerated fewer repeat trials overall than age-matched BALB/c mice. Induced autoresuscitation failure in all mice appeared to be unrelated to gasping regulation, because both gasp number and amplitude were similar during the failed trial and the previous successful trial. In most mice, failure was associated with absent recovery of heart rate during gasping. In BALB/c mice in particular, this persistent bradycardia was usually due to heart block, which occurred in 95% of failed trials. In addition, heart block occurred with increasing frequency on later successful trials, but conversion to sinus rhythm always preceded successful autoresuscitation. Heart block was also frequent in SWR mice and had similar consequences. BALB/c mice exposed to continuous anoxia survived longer than SWR mice, indicating increased endurance of components of the autoresuscitation mechanism not directly related to the ventilatory function of gasping (e.g., cardiovascular components).(ABSTRACT TRUNCATED AT 250 WORDS)     

Das Lungenkrebsrisiko Durch Inhalation von Radon-222-Zerfallsprodukten

Zusammenfassung Es werden die Ergebnisse der in den USA und in der CSSR durchgeführten Erhebungen über die Lungenkrebshäufigkeit bei Uranbergarbeitern gegenübergestellt und verglichen. An Hand dieser Daten wird der Zusammenhang zwischen der beobachteten erhöhten Lungenkrebsmortalität und der durch Rn-Zerfallsprodukte verursachten Strahlenexposition bei diesen Arbeitern diskutiert und der Risikokoeffizient für strahleninduzierten Lungenkrebs abgeschätzt. Der relative Risikokoeffizient stimmt bei beiden Kollektiven von Uranbergarbeitern innerhalb der Vertrauensgrenzen überein und liegt im Bereich von 0,001 bis 0,005 WLM^–1. Demgegenüber besteht zwischen dem abgeleiteten absoluten Risikokoeffizienten von etwa 20±10 (USA-Kollektiv) bzw. 150±50 (CSSR-Kollektiv) zusätzliche Lungenkrebsfälle pro WLM und 10⁶ Personen ein signifikanter Unterschied. Der Einfluß synergistischer bzw. kocancerogener Effekte wird diskutiert. Die Zunahme der Lungenkrebsmortalität mit steigender Exposition ist signifikant verknüpft mit einer Zunahme des kleinzeiligen, undifferenzierten Krebszelltyps.

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The lung cancer risk by inhalation of Rn-222-decay products

Summary The results of surveys in the USA and the CSSR about the lung cancer mortality among uranium miners are compared. The relation between the observed excess lung cancer mortality and the cumulative exposure of these miners by inhaled Rn-daughters is discussed and the risk coefficients for radiation-induced lung cancer are estimated. The relative risk coefficients of both study groups of U-miners agree within the confidence limits and are in the range of 0,001 to 0,005 WLM^–1. The derived absolute risk coefficients of 20±10 (USA group) and 150±50 (CSSR group) additional lung cancer deaths per WLM and 10⁶ miners are, however, significantly different. The influence of synergistic or cocancerogenic actions is discussed. The increase of lung cancer mortality with Rn-exposure is significantly correlated with an increase of the small-cell, undifferentiated type of carcinoma.

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Herrn Prof. Dr. Dr. h. c. mult. B. Rajewsky zum 80. Geburtstag gewidmet.     

Feeding of Arapaima sp.: integrating stomach contents and local ecological knowledge

The giant arapaima (Arapaima sp.) has been described as a fish of change in Amazonia because of its important role in the conservation of floodplains, food security and income generation for rural communities. Nonetheless, despite the cultural, ecological and economic importance of arapaima, data on diet are scarce. Aiming to expand knowledge about arapaima diet in western Amazonia, scientific knowledge was integrated with the knowledge of local dwellers. During the low-water period (September 2018) and the falling-water period (June 2019), arapaima stomachs were collected from 11 floodplain lakes in the middle Juruá River. All fishes were measured [TL (total length)] and sexed. Food items from each stomach were categorized as fishes, invertebrates, plants and bone remains and weighed. Also, in the latter period, experienced local fishers were interviewed about arapaima feeding. This integrated approach revealed that young arapaima eat fish and invertebrates but adult arapaima eat fish of a wide range of species, which were mainly of low and intermediate trophic positions. This study reports the first case of cannibalism for arapaima and also shows that during the low-water period, many individuals had empty stomachs or only some small fish-bone remains and/or plant material. Arapaima sex and TL had no influence on the absence of prey in stomach contents. Overall, it can be concluded that local people had consistent ethnobiological knowledge of arapaima feeding ecology that could be useful within management projects in the region.     

Quantitation of heteroplasmy in mitochondrial DNA mutations by primer extension using Vent(R)(exo-) DNA polymerase and RFLP analysis

In this report we describe a simple and rapid protocol for reliable quantitation of mitochondrial DNA (mtDNA) mutations, which is basically a modification of the traditional polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) analysis technique. Up to now, the PCR/RFLP method has been of limited use for the accurate determination of ratios of mutant and wild type molecules, largely owing to the formation of heteroduplex molecules by PCR and incompleteness of restriction digestion. In order to overcome this problem, we have introduced a single-step primer extension reaction using Vent(R)(exo-) DNA polymerase and a fluorescence-labeled primer to the standard assay. The labeled homoduplex molecules are then digested with a restriction endonuclease, and the nucleic acids fractionated on an automated DNA sequencer equipped with GENESCAN analysis software. The amount of mutant mtDNA is readily estimated from fluorescence intensities of the wild-type and mutant mtDNA fragments corrected for incomplete digestion as monitored by a homologous control fragment. The accuracy of the improved protocol was determined by constructing standard curves obtained from defined mixtures of genomic DNA containing homoplasmic wild-type and mutant mtDNA. The expected values were obtained, with an observed correlation coefficient of 0.997 and a typical variability of +/-5% between repeated measurements. Further validation of the protocol is provided by the screening of five patients and unaffected subjects carrying the guanine to adenine transition at the nucleotide 3460 of the mitochondrial genome responsible for the mitochondrial disorder of Leber's hereditary optic neuropathy.