Identification of an S-locus glycoprotein allele introgressed from B. napus ssp. rapifera to B. napus ssp. oleifera.

We have previously described a developmentally regulated mRNA in maize that accumulates in mature embryos and is involved in a variety of stress responses in the plant. The sequence of the encoded 16 kDa protein (MA16) predicts that it is an RNA-binding protein, since it possesses a ribonucleoprotein consensus sequence-type RNA-binding domain (CS-RBD). To assess the predicted RNA binding property of the protein and as a starting point to characterize its function we have used ribohomopolymer-binding assays. Here we show that the MA16-encoded protein binds preferentially to uridine- and guanosine-rich RNAs. In light of these results a likely role for this protein in RNA metabolism during late embryogenesis and in the stress response is discussed.     

Inhibition of a nutrient-dependent pinocytosis in dictyostelium discoideum by the amino acid analogue hadacidin

In the present study we examine the effects of the drug hadacidin (N-formyl-N- hydroxyglycine) on pinocytosis in the eukaryotic microorganism dictyostelium discoideum. At concentrations of up to approximately 8 mg/ml, hadacidin inhibited the rate of pinocytosis of fluorescein isothiocyanate (FITC) dextran in cells in growth medium in a concentration-dependent manner but had no effect on cells in starvation medium. Because hadacidin also inhibits cellular proliferation at this concentration, the relationship between growth rate and pinocytosis was studied further using another drug, cerulenin, to produce growth-arrest. These experiments showed no changes in the rate pinocytosis even after complete cessation of cellular proliferation. Other studies showed that the transfer of cells from growth to starvation medium reduced the rate of pinocytosis by approximately 50 percent. A reduction of similar magnitude occurred if cells were transferred from growth to starvation medium containing hadacidin. Also, no additional reduction in pinocytosis occurred when cells that had been treated with hadacidin were transferred to starvation medium containing hadacidin. These cells were able to take up [(14)C]hadacidin in the starvation medium. In contrast to the results with hadacidin-treated cells, cells in a cerulenin-induced state of growth-arrest when transferred to starvation medium exhibited the same 50 percent reduction in pinocytosis observed in cells not previously exposed to either drug. Cells treated with azide, in either growth or starvation medium, exhibited an immediate inhibition of all pinocytotic activity. After the transfer of log-phase cells to starvation medium supplemented with glucose, the reduction in rate was only approximately 10-15 percent. In contrast, a 50 percent reduction was observed after supplementation of starvation medium with sucrose, KCl, or concanavalin A. Maintaining the cells in growth medium containing hadacidin for as long as 16 h had no effect on the rate at which cells aggregated. These results are consistent with the conclusion that D. discoideum exhibits two types of pinocytotic activity: one that is nutrient dependent and the other independent of nutrients. This latter activity persists in starvation medium and is unaffected by hadacidin, whereas the nutrient-dependent activity is present in growth medium and is inhibited by hadacidin.     

Asymmetric incorporation of 4-(2′-carboxyphenyl)-4-oxobutyrate into phylloquinone by Zea mays

Radioactivity from 4-(2′-carboxyphenyl)-4-oxobutyrate-[2-¹⁴C] and 4-(2′-carboxyphenyl)- 4-oxobutyrate-[3-¹⁴C] was incorporated into C-3 and C-2 respectively of phylloquinone in maize shoots. These results show that this substrate is incorporated in the same asymmetric manner into phylloquinone as it is into the bacterial menaquinones.     

Phosphoric acid triester–glutathione alkyltransferase. A mechanism for the detoxification of dimethyl phosphate triesters

1. 2-Chloro-1-(2,4,5-trichlorophenyl)vinyl dimethyl phosphate (tetrachlorvinphos) is demethylated by mammalian liver supernatant (100000g) protein in the presence of GSH. 2. GSH acts as an acceptor of the transferred methyl group to form S-methyl glutathione. 3. The enzyme that catalyses this reaction is present in the soluble fraction of liver from mouse, rat, rabbit and pig at similar activity. The enzyme was purified 45-fold from pig liver, dimethyl 1-naphthyl phosphate being used as assay substrate. 4. Methyl groups are readily removed from most of the substrates studied; ethyl groups are removed at one-fiftieth to one-hundredth of the rate for methyl groups. It is likely that the enzyme plays an important role in the detoxification of the phosphate triester pesticides containing CH(3)-O-P groups.     

Studies on carbohydrate-metabolizing enzymes. The hydrolysis of α-glucosides, including nigerose, by extracts of alfalfa and other higher plants

1. Enzyme preparations from 11 plant sources, from yeast and from the protozoan Tetrahymena pyriformis show nigerase activity, which, in most preparations, was 70–90% of that towards maltose. 2. These enzyme preparations also hydrolysed isomaltose, but there was a wide variation in relative maltase to isomaltase activity. 3. The maltase and nigerase activities of alfalfa and tomato preparations could not be differentiated by heat inactivation or inhibitor methods. However, with turanose used as a competitive inhibitor, evidence suggesting that maltose and nigerose are hydrolysed at different catalytically active sites in the alfalfa preparation was obtained. 4. It is probable that the alfalfa α-glucosidase exists as a mixture of isoenzymes.     

Determination of Daily Variations of Brain 5-Hydroxytryptamine and Dopamine Turnovers and of the Clearance of Their Acidic Metabolites in Conscious Rats by Repeated Sampling of Cerebrospinal Fluid

Central 5-hydroxytryptamine (5-HT) and dopamine (DA) turnovers were estimated simultaneously in conscious freely moving rats kept on a 12-h dark/12-h light cycle by sampling cisternal CSF of each animal before and after giving probenecid and determining the accumulation of the acidic metabolites of the two amines. The turnovers of both transmitters and the clearances of their acid metabolites from the brain were shown to be significantly greater during the dark (red light) period than during the white light period.     

Effect of retinol and retinoic acid on testosterone production by rat Leydig cells in primary culture

Adult rat Leydig cells, purified by Percoll density gradient centrifugation, were used to determine the effect of retinol and retinoic acid on steroidogenesis. It was found that both retinoic acid and retinol stimulated testosterone production. Although retinol was less potent than retinoic acid, retinol had the greater efficacy. When these retinoids were tested in the presence of a maximal dose of LH, it was found that retinol inhibited LH-stimulated testosterone synthesis whereas retinoic acid had no similar effect. These results demonstrate for the first time that retinol and retinoic acid have a direct effect on Leydig cell steroidogenesis in culture suggesting that retinoids play a role in the maintenance and regulation of Leydig cell function.     

31P NMR visibility and characterization of rat liver mitochondrial matrix adenine nucleotides

Compartmentation and NMR visibility of mitochondrial adenine nucleotides were quantitated in isolated rat liver mitochondria respiring on succinate and glutamate in vitro at 8 and 25 degrees C. Intra- and extramitochondrial nucleotides were discriminated by adding the chelator trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA). T1 values of about 0.2-0.3 s for magnesium-bound matrix nucleotides were determined. Adenine nucleotide T1 values were influenced by the ionic environment; only magnesium-free ATP T1's were affected by temperature. Intra- and extramitochondrial adenine nucleotide ratios were varied in ATP-loaded mitochondria with added ATP and phosphate using the mitochondrial inhibitors oligomycin and carboxyatractyloside, and adenine nucleotides were quantitated by using NMR and enzymatic analysis. There was good agreement between matrix ATP concentrations (magnesium-bound ATP) calculated by using NMR and standard biochemical techniques. Although matrix ADP could be detected by NMR, it was difficult to quantitate accurately by NMR. The data indicate that mitochondrial ATP is NMR-visible in isolated mitochondria in vitro.