Effect of methionine sulfoximine on asparaginase activity and ammonium levels in pea leaves

In developing leaves of Pisum sativum the levels of ammonium did not change during the light-dark photoperiod even though asparaginase (EC 3.5.1.1) did; asparaginase activity in detached leaves doubled during the first 2.5 hours in the light. When these leaves were supplied with 1 millimolar methionine sulfoximine (MSX, an inhibitor of glutamine synthetase, GS, activity) at the beginning of the photoperiod, levels of ammonium increased 8-to 10-fold, GS activity was inhibited 95%, and the light-stimulated increase in asparaginase activity was completely prevented, and declined to less than initial levels. When high concentrations of ammonium were supplied to leaves, the light-stimulated increase of asparaginase was partially prevented. However, it was also possible to prevent asparaginase increase, in the absence of ammonium accumulation, by the addition of MSX together with aminooxyacetate (AOA, which inhibits transamination and some other reactions of photorespiratory nitrogen cycling). AOA alone did not prevent light-stimulated asparaginase increase; neither MSX, AOA, or elevated ammonium levels inhibited the activity of asparaginase in vitro. These results suggest that the effect of MSX on asparaginase increase is not due solely to interference with photorespiratory cycling (since AOA also prevents cycling, but has no effect alone), nor to the production of high ammonium concentration or its subsequent effect on photosynthetic mechanisms. MSX must have further inhibitory effects on metabolism. It is concluded that accumulation of ammonium in the presence of MSX may underestimate rates of ammonium turnover, since liberation of ammonium from systems such as asparaginase is reduced by the effects of MSX.     

Moral medicine: Symbolic content in 19th century Shaker therapeutics

This paper presents an analysis of the symbolic meanings implicit in an ostensibly empirical therapeutic system. The Shakers, a celibate communal religious order founded in New York State in the mid 1770s, were practitioners of botanic medicine, as were many other Americans in the nineteenth century. This study analyzes the therapeutic properties of the herbs they produced (such as diuretic, stimulant, narcotic, emetic, astringent), using a classification scheme based on the location of the botanical substance's effect vis-à-vis body boundaries and surfaces. The Shakers' beliefs about the therapeutic properties of their herbs are compared with similar analyses of the properties given by two contemporary nineteenth century New England proponents of herbal medicine, botanist Constantine Rafinesque and sectarian practitioner Samuel Thomson. The comparison shows systematic variation in emphasis given to herbs which regulate internal body processes, or act through the openings of the body or on its surface. In this context Shaker medicine can be characterized as quickening, internal, and purifying in its effects on body processes, effects which are highly consistent with Shaker religious beliefs in active, physical worship, selflessness and spiritual purification by confession.     

Partial purification and characterization of a cellular protein that binds to the SV40 core origin of DNA replication

A monkey cell factor that interacts specifically with double- and single-stranded DNA sequences in the early domain of the simian virus 40 (SV40) core origin of replication was identified using gel-retention assays. The protein was enriched over 1200-fold using ion-exchange and affinity chromatography on single-strand DNA cellulose. Binding of protein to mutant origin DNA restriction fragments was correlated with replication activity of the mutant DNAs. Exonuclease footprint experiments on single-stranded DNA revealed prominent pause sites in the early domain of the core origin. The results suggest that this cellular protein may be involved in SV40 DNA replication.     

Distribution of the Glucose-1,6-Bisphosphate System in Brain and Retina

The distribution of glucose-1,6-bisphosphate (G16P2) synthase was measured in more than 70 regions of mouse brain, and nine layers of monkey retina. Activities in gray areas varied as much as 10-fold, in a hierarchical manner, from highest in telencephalon, especially the limbic system, to lowest in cerebellum, medulla, and spinal cord. The synthase levels were significantly correlated among different regions with G16P2 itself, as well as with previously published levels of a brain specific IMP-dependent G16P2 phosphatase. In contrast, neither G16P2 nor either its synthase or phosphatase correlated positively with phosphoglucomutase, and in all regions the G16P2 levels greatly exceeded requirements for activation of this mutase. This strengthens the view that G16P2 has some function besides serving as coenzyme for phosphoglucomutase. However, attempts to correlate the "G16P2 system," as defined by the three coordinately related elements, synthase, phosphatase, and G16P2, with other enzymes of carbohydrate metabolism, or with regional data of Sokoloff et al. [J. Neurochem. 28, 897-916 (1977)] for glucose consumption, were unsuccessful. This leaves open the possibility that brain G16P2 might serve as a phosphate donor for specific nonmetabolic effector proteins.     

Dinitrogenase reductase (Fe-protein) of nitrogenase in the cyanobacterial symbionts of three Azolla species: Localization and sequence of appearance during heterocyst differentiation

Transmission electron microscopy and immunocytological labeling were used to study the distribution and ontological occurrence of dinitrogenase reductase (Fe-protein) of nitrogenase in cyanobacterial symbionts within young leaves of the water-ferns Azolla filiculoides Lamarck, A. caroliniana Willdenow, and A. pinnata R. Brown. Rabbit anti-dinitrogenase reductase antisera and goat anti-rabbit-immunoglobulin G antibody conjugated to colloidal gold were used as probes. Western blot analyses showed that a polypeptide of approx. 36 kDa (kdalton) was recognized in the symbionts of all three Azolla species and that the polyclonal sera used were monospecific. In all symbionts, nitrogenase was immunologically recognizable within heterocysts. It was absent from vegetative cells, and also from the akinetes of the A. caroliniana and A. pinnata symbionts. The differentiation of vegetative cells into heterocysts in all three symbionts was initiated by formation of additional external cell-wall layers and narrowing of the neck followed by loss of glycogen, mild vesiculation of thylakoid membranes, and the appearance of polar nodules. No nitrogenase was detected at these early stages, but it appeared in the intermediate proheterocyst stage concomitantly with the formation of contorted membranes, and reached the strongest labeling in mature heterocysts, containing extensive tightly packed membranes. Nitrogenase was evenly distributed throughout heterocysts except at the polar regions, which contained honey-comb configurations and large polar nodules. With increased age of the A. caroliniana and A. pinnata symbionts, heterocysts became highly vesiculated, with a concomitant decrease in the amount of nitrogenase detected.Abbreviations IgG Immunoglobulin G - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate - TEM transmission electron micrograph     

A plastome mutation affects processing of both chloroplast and nuclear DNA-encoded plastid proteins

Summary A bovine tRNA gene cluster has been characterized and the sequences of four tDNAs determined. Two of the tDNAs could encode tRNA^Ser _IGA, one tDNA^Ser _UGA, and the fourth tRNA^Gln _CUG. The three serine tDNAs representing the UCN codon isoacceptor family are almost identical. However, the sequence of the tDNA^Ser _TGA differs from a previously sequenced bovine tDNA^Ser _TGA at 12 positions (ca. 14%). This finding suggests that in the bovine genome, two subfamilies of genes might encode tRNA^Ser _UGA. It also raises the possibility that new genes for a specific UCN isoacceptor might arise from the genes of a different isoacceptor, and could explain previously observed differences between species in the anticodons of coevolving pairs of tRNAs^Ser _UCN. The gene cluster also contains complete and partial copies, and fragments, of the BCS (bovine consensus sequence) SINE (short interspersed nuclear element) family, six examples of which were sequenced. Some of these elements occur in close proximity to two of the serine tDNAs.     

Pseudocyphellaria dissimilis: a desiccation-sensitive,highly shade-adapted lichen from New Zealand

Summary Pseudocyphellaria dissimilis, a foliose, cyanobacterial lichen, is shown not to fit into the normal ecological concept of lichens. This species is both extremely shade-tolerant and also more intolerant to drying than aquatic lichens previously thought to be the most desiccation-sensitive of lichens. Samples of P. dissimilis from a humid rain-forest site in New Zealand were transported in a moist state to Germany. Photosynthesis response curves were generated. The effect of desiccation was measured by comparing CO₂ exchange before and after a standard 20-h drying routine. Lichen thalli could be equilibrated at 15° C to relative humidities (RH) from 5% to almost 100%. Photosynthesis was saturated at a photosynthetically active radiation (PAR) level of 20 mol m^-2 s^-1 (350 bar CO₂) and PAR compensation was a very low 1 mol m^-2 s^-1. Photosynthesis did not saturate until 1500 bar CO₂. Net photosynthesis was relatively unaffected by temperature between 10° C and 30° C with upper compensation at over 40° C. Temporary depression of photosynthesis occurred after a drying period of 20 h with equilibration at 45–65% relative humidity (RH). Sustained damage occurred at 15–25% RH and many samples died after equilibration at 5–16% RH. Microclimate studies of the lichen habitat below the evergreen, broadleaf forest canopy revealed consistently low PAR (normally below 10–20 mol m^-2 s^-1) and high humidities (over 80% RH even during the day time). The species shows many features of an extremely deep shade-adapted plant including low PAR saturation and compensation, low photosynthetic and respiratory rates and low dry weight per unit area.     

Regulation of Phytochrome Message Abundance in Root Caps of Maize : Spatial, Environmental, and Genetic Specificity

In many cultivars of maize (Zea mays L.) red light affects root development via the photomorphogenetic pigment phytochrome. The site of perception for the light is the root cap. In the maize cultivar Merit, we investigated phytochrome-mediated events in the cap. We established that the message encoded by the phyA1 gene was most abundant in dark-grown tissue and was asymmetrically distributed in the root cap, with greatest expression in the cells which make up the central columella core of the cap. Phytochrome message was negatively autoregulated in a specific region within the root cap. This autoregulation was sensitive to very-low-fluence red light, and thus was characterized as a phytochrome-mediated, very-low-fluence event. The kinetics of message reaccumulation in the dark were also examined and compared to the kinetics of the light requirement for root gravitropism in this cultivar. Similarly, the degree of autoregulation present in two other maize cultivars with different light requirements for gravitropic sensitivity was investigated. It appears that the Merit cultivar expresses a condition of hypersensitivity to phytochromemediated light regulation in root tissues. We conclude that phytochrome regulates many activities within the cap, but the degree to which these activities share common phytochrome-mediated steps in not known.     

Stimulation of rat Sertoli cell adenylate cyclase by germ cells in vitro

The effect of germ cells or germ cell fractions on adenylate cyclase (AC) activity in membrane preparations from cultured rat Sertoli cells has been examined. Whole germ cells or 30,000 X g pellet or supernatant fractions of germ cells have the ability to stimulate Sertoli cell AC to levels comparable to those measured in follicle-stimulating hormone-stimulated Sertoli cell membranes. Treatment at 100 degrees C but not 60 degrees C for 1 min abolished the ability of germ cell preparations to stimulate Sertoli AC. Germ cell stimulation of Sertoli cell AC was not calcium dependent, was not blocked by propranolol, and was observed to be dose dependent.