Photosynthesis and nitrogen utilization in exponentially growing nitrogen-limited cultures of Lemna gibba

The photosynthetic performance and nitrogen utilization of Lemna gibba L. G3 adapted to limited nitrogen supply was studied. The plants were adapted to two levels of nitrogen limitation where the nitrogen addition rates were calculated to sustain relative growth rates (RGR) of 0.15 day^?1 and 0.25 day^?1, respectively. The photosynthetic performance of these cultures was compared to nitrogen-sufficient cultures with an average RGR of 0.32 day^?1. Plants transferred from nitrogen-sufficient conditions attained RGR values corresponding to the nitrogen addition rates after 6 to 10 days. Light-saturated net photosynthesis declined during adaptation according to the drop in growth rate, and a concomitant decrease in the respiration rate was recorded. The efficiency of net photosynthesis on a dry weight basis increased with increased nitrogen supply, whereas it was the same in all cultures when expressed on a chlorophyll basis. The light compensation point was unaffected by the nitrogen regime. Limited nitrogen supply resulted in an increased proportion of dry matter in the roots, which led to decreased leaf area ratios. The net assimilation rates also decreased, but not to the same extent as the leaf area ratios. Growth-limiting amounts of nitrogen were added to the cultures once daily, and the net influx of N was higher than the requirement for N, also in adapted cultures with a steady growth rate. This resulted in transient, periodic fluctuations in the NO₃^?, NH₄⁺ and amino acid pools. Also the rates of NO₃^? reduction and NH₄⁺ assimilation fluctuated as did the amino acid assimilation which paralleled NH₄⁺ assimilation. The role of flux rates over the plasmalemma and tonoplast for control of nitrogen assimilation rates are discussed.     

Suproxide dismutase in human testis preparations

A protein fraction from human testis was structurally investigated. The main component of the fraction reported to contain inhibin-like activity was purified and analyzed by tryptic digestion. The peptides obtained identified the protein as an enzyme, superoxide dismutase, previously known to be present in seminal plasma. The results show that superoxide dismutase is a major enzyme, also of testicular material. They further demonstrate the importance of using pure fractions, and controls such as checks with structural analysis or synthetic peptides, in the work of elucidating the nature of inhibin and other hormonal peptides.     

Synthesis of mannose oligosaccharides via reversal of the α-mannosidase reaction

Summary Three naturally occurring isomers of the disaccharideO--d-mannosyl-d-mannoside were synthesized by reversing the hydrolytic activity of jack bean -mannosidase at 75°C in a very high concentration of mannose. Higher oligosaccharides were also obtained at the later stages of the reaction. The maximum total yield of disaccharides was 37% (w/w) based on the total amount of saccharides.     

Evidence for PHI-immunoreactive nerve fibres in the human skin: coexistence with VIP?

Using indirect immunofluorescence methodology, PHI-like immunoreactivity was found in a certain subpopulation of nerve fibres and terminals of the human skin. The immunoreactive fibres were mainly seen close to and around blood vessels and sweat glands, and they were of a fine-calibre type with smooth preterminal axons and a sparse plexus of varicosities at their terminal field. Furthermore, they were also observed around hair follicles, though more rarely around sebaceous glands. Finally, single PHI immunoreactive fibres could be seen in the close vicinity of the erector pili muscles. These fibres in all probability represent peripheral branches of the autonomic nervous system. Single (somatic?) immunoreactive fibers were, however, also found in the apical parts of the dermis, close to the epidermal-dermal junctional zone. The occurrence of VIP was also analysed and found to be similar to that of PHI. Thus, the present data point to a probable coexistence of PHI and VIP, a possibility that should be taken into account when discussing functional effects of VIP in human skin.     

Recovery of proteins on a milligram scale from polyacrylamide electrophoresis gels,exemplified by purification of a retinol-binding protein

An apparatus suitable for the recovery of proteins from polyacrylamide gels on a milligram scale by displacement electrophoresis (isotachophoresis) is described along with a buffer system that is suitable for this purpose with most proteins. The technique is illustrated by the recovery of a protein from a 15% polyacrylamide gel. The recovery was almost quantitative and the eluted protein showed little contamination upon quantitative amino acid analysis and automatic Edman degradation.     

Control of Adenovirus Gene Expression: Cellular Gene Products Restrict Expression of Adenovirus Host Range Mutants in Nonpermissive Cells

Adenovirus type 5 (Ad5) host range mutants dl312 and hr-1, with lesions in region E1A (0 to 4.5 map units) of the viral genome, fail to accumulate virus-specific early RNA during infection in HeLa cells. In a recent report, we showed that the addition of anisomycin, a stringent inhibitor of protein synthesis, at 1 h after infection of HeLa cells with hr-1 virus resulted in the accumulation of properly spliced and translatable mRNA from all early regions (M. G. Katze, H. Persson, and L. Philipson, Mol. Cell. Biol. 1:807-813, 1981). Based on these results we proposed a model in which expression of early mutant RNA was achieved through inactivation of a cellular protein normally causing a reduction in the amount of viral RNA. These studies have been extended in the present report, which shows that early viral proteins can be detected in Ad5 dl312- and Ad5 hr-1-infected HeLa cells which have been treated for several hours with anisomycin either shortly after infection or before infection. A pulse of drug treatment also resulted in expression of substantial amounts of adenovirus structural proteins after infection with both Ad5 hr-1 and Ad5 dl312, whereas in drug-free controls no late proteins were detected. The Ad5 hr-1 virus previously reported to be DNA replication negative in nonpermissive HeLa cells was found to replicate its DNA, albeit at low levels, when anisomycin was present either from 1 to 5 h postinfection or for 5 h before infection. When infectious virus production was examined in mutant-infected cells the titer of Ad5 dl312 virus was found to increase at least 500-fold in anisomycin-treated HeLa cells. Taken together, these and our previous results suggest that the block in gene expression characteristic for complementation group I Ad5 host range mutants in HeLa cells can be overcome by inactivating cellular gene products serving as negative regulators of viral gene expression.     

The incorporation of selenium and alterations of macro- and trace element levels in individual blood cells following supplementation with sodium selenite and vitamin E

Significant alterations in the selenium content of erythrocytes, thrombocytes, and neutrophil granulocytes were observed following a daily supplementation of 200 μg Se + 100 mg vitamin E during a period of 2 months. The neutrophil granulocytes incorporated more selenium than the thrombocytes. The iron content of the thrombocytes decreased on selenium supplementation, while the opposite was noted for the neutrophil granulocytes. The glutathione peroxidase activity was not significantly changed during the period of observation.