Choline: high-affinity uptake by rat brain synaptosomes

Synaptosomes from rat brain accumulate choline by two kinetically distinct processes, a high-affinity uptake system [Michaelis constant (K(m)) = 1 x 10(-6)M], and a low-affinity system (K(m) = 9 x 10(-5)M). The high-affinity uptake system requires sodium, and is associated with considerable formation of acetylcholine. The low-affinity uptake system is less dependent on sodium, and does not appear to be associated with a marked degree of acetylcholine formation. The high-affinity choline uptake appears to represent selective choline accumulation by cholinergic neurons.     

Recognition sites for norepinephrine uptake: regulation by neurotransmitter

Recognition sites for the uptake of norepinephrine on adrenergic neurons in the brain and periphery were labeled with [3H]desipramine. The number of these uptake sites varied with the concentration of transmitter; depletion of norepinephrine with reserpine reduced the number of uptake sites, whereas increasing the concentration of norepinephrine induced by treatment with monoamine oxidase inhibitors raised the number of binding sites. These dynamic alterations in norepinephrine uptake recognition sites may regulate synaptic function homeostatically, providing less inactivation of reuptake when the synaptic concentration of the transmitter is low and increased inactivation when it is high.     

Amino acid uptake by kidney and jejunal tissue from dogs with cystine stones

Cystine and lysine accumulation in vitro in intestinal and renal tissue was studied in eight dogs that form cystine stones. Under conditions which demonstrate in vitro defects in tissue obtained from humans with cystinuria, normal amino acid accumulation occurred in six dogs with the canine disorder. Normal amino acid uptake in tissue and the demonstration of normal to minimum increases in excretion of lysine suggest that the canine disorder is not similar to the human syndrome.     

Reticulocyte protein synthesis: response of ribosome fractions to polyuridylic acid

Reticulocyte ribosomes with sedimentation coefficients greater than 100S ("heavy" ribosomes) appear to be considerably more active in hemoglobin synthesis than are 78S ribosomes. When assayed for the ability to synthesize polyphenylalanine in the presence of polyuridylic acid, the 78S ribosomes and "heavy" ribosomes have similar activities. Polyuridylic acid inhibits incorporation by "heavy" ribosomes of amino acids other than phenylalanine.     

Amino acid changes provoked by streptomycin in a polypeptide synthesized in vitro

The misincorporation of isoleucine provoked by streptomycin in a polyuridylate-directed incorporating system from Escherichia coli has been examined by a double-labeling technique with phenylalanine-(3)H and isoleucine-(14)C. The polypeptides synthesized are associated with 70S ribosomes and contain only phenylalanine in the absence of streptomycin, and both phenylalanine and isoleucine in the presence of the antibiotic. Results of acid hydrolysis and subsequent chymotryptic digestion of the polypeptides indicate that the misincorporated amino acid is inserted by peptide bonding with phenylalanine and is randomly distributed along the chain.     

Amino acid sequences common to rapidly degraded proteins: the PEST hypothesis

The amino acid sequences of ten proteins with intracellular half-lives less than 2 hours contain one or more regions rich in proline (P), glutamic acid (E), serine (S), and threonine (T). These PEST regions are generally, but not always, flanked by clusters containing several positively charged amino acids. Similar inspection of 35 proteins with intracellular half-lives between 20 and 220 hours revealed that only three contain a PEST region. On the basis of this information, it was anticipated that caseins, which contain several PEST sequences, would be rapidly degraded within eukaryotic cells. This expectation was confirmed by red blood cell-mediated microinjection of 125I-labeled caseins into HeLa cells where they exhibited half-lives of less than 2 hours. The rapid degradation of injected alpha- and beta-casein as well as the inverse correlation of PEST regions with intracellular stability indicate that the presence of these regions can result in the rapid intracellular degradation of the proteins containing them.     

Linoleic acid hydroperoxide: impaired bacterial uptake by alveolar macrophages, a mechanism of oxidant lung injury

Exogenous linoleic acid hydroperoxide causes in vitro impairment of both bacterial uptake and the phagocytic stimulation of (14)CO(2) production from [1-(14)C]glucose in rabbit alveolar macrophages by an undefined effect on the cell membrane. This effect may be one mechanism for the defective pulmonary bacterial clearance characteristic of oxidant lung injury.     

Amino acid transport: evidence for genetic control of two types in human kidney

A mutation affecting renal transport of proline, hydroxyproline, and glycerine occurs in man. In the presumed homozygote there is still significant residual transport of these compounds; however, this remaining function is saturated at normal concentrations of substrate in the plasma and is not inhibited by L-proline in the expected way. The presumed heterozygote has partial loss of a transport system common to the three substrates, which becomes saturated at high concentrations of substrate and is inhibited by L-proline. Two different types of transport systems are proposed: a common system and systems with lower capacity and greater specificity. The two types of transport appear to be controlled by separate genes.     

外源柠檬酸对3种观赏植物吸收和转运镉的影响

为了探究柠檬酸与植物联合修复镉污染土壤的效果,采用盆栽试验,研究外源柠檬酸的添加对萱草(Hemerocallis fulva)、鸢尾(Iris tectorum Maxim.)和美人蕉(Canna indica L.)3种观赏植物修复镉污染土壤的影响.结果表明:(1)与CK和未添加柠檬酸处理组相比,柠檬酸添加显著降低了土壤的pH值.(2)柠檬酸的添加显著改善了萱草、鸢尾和美人蕉的生长状况,植物的株高、根长和生长量最大值均出现在添加柠檬酸中浓度镉污染(Tm)处理中,其单株生物量最高值分别为13.97、23.92和56.95 g.(3)在CK和未添加柠檬酸处理组中,萱草、鸢尾和美人蕉的地上部分镉含量低于地下部分,其差值变化范围分别为-5.09～-41.06、-6.44～-49.77和-15.35～-53.80mg·kg-1;而柠檬酸的添加促进了地下部分镉向地上部分的转移,使地上部分镉含量高于地下部分,其差值变化范围分别为9.98～42.50、9.51～44.93和16.10～47.59 mg·kg-1.(4)萱草、鸢尾和美人蕉3种观赏植物在添加柠檬酸处理组中的转运系数大于1,显著增加了植株地上部分的镉积累量,且美人蕉的地上部分和地下部分镉积累量明显高于萱草和鸢尾,其最高值分别为7 603.39和1 545.60 μg·株-1.综上所述,萱草、鸢尾和美人蕉3种观赏植物均可作为土壤镉污染修复植物使用,添加柠檬酸可有效提高3种观赏植物对镉污染土壤的修复效率.美人蕉由于植株高大和块状根茎的特性,使其表现出比萱草和鸢尾更强大的镉修复能力.     

Dieldrin: extraction of accumulations by root uptake

Certain forage crops can absorb and translocate the chlorinated hydrocarbon insecticide dieldrin from soil or sand. An extraction technique routinely used for analyses of residues does not quantitatively remove this internal chemical, but a method employing chloroform-methanol extraction leads to essentially quantitative recovery.     

Interferon: lack of detectable uptake by cells

No interferon, or at most a small fraction of that applied, is taken up by cells during the period of induction of antiviral activity. The lack of detectable adsorption was not influenced either by the concentration of interferon or the volume. The results were similar in both chicken and mouse systems.     

Amino acid acylation: a mechanism of nitrogen excretion in inborn errors of urea synthesis

Treatment of a patient deficient in carbamyl phosphate synthetase with benzoate or phenylacetic acid resulted in an increase in urinary nitrogen, which could be accounted for by the respective amino acid acylation product, hippurate or phenylacetylgultamine. Benzoate treatment of four hyperammonemic comatose patients led to clinical improvement and a return of plasma ammonium levels toward normal.     

Cadmium: uptake by vegetables from superphosphate in soil

Phosphates in fertilizers contain cadmium. When vegetables usually devoid of cadmium were grown in soil heavily fertilized with 20 percent superphosphate, they absorbed it. Vegetables normally containing cadmium absorbed larger quantities in the presence of superphosphate and little or none in its absence. The superphosphate showed 7.25 parts of cadmium per million. Five grains usually containing cadmium were grown in unfertilized soil poor in this element; four did not absorb it. Phosphate fertilizers may be a source of the cadmium in some vegetable foods.     

How cats lap: water uptake by Felis catus

Animals have developed a range of drinking strategies depending on physiological and environmental constraints. Vertebrates with incomplete cheeks use their tongue to drink; the most common example is the lapping of cats and dogs. We show that the domestic cat (Felis catus) laps by a subtle mechanism based on water adhesion to the dorsal side of the tongue. A combined experimental and theoretical analysis reveals that Felis catus exploits fluid inertia to defeat gravity and pull liquid into the mouth. This competition between inertia and gravity sets the lapping frequency and yields a prediction for the dependence of frequency on animal mass. Measurements of lapping frequency across the family Felidae support this prediction, which suggests that the lapping mechanism is conserved among felines.     

锰对外生菌根真菌生长、养分吸收及有机酸分泌的影响

在液体培养条件下,研究了不同质量浓度锰对外生菌根真菌Pt 715、Sl 13和Cg 04菌丝生长、草酸和乙酸分泌,以及氮、磷、钾吸收的影响。结果表明:Pt 715的生物量最高, Sl 13次之,Cg 04最低。锰显著抑制菌丝生长,菌丝生物量（y）与培养基中的锰质量浓度（0～800 mg/L）呈y=ax+b的关系（a0）;但锰对Pt 715和Sl 13生长的抑制作用较小,说明这2株外生菌根真菌抗锰能力较强,其原因可能是它们长期生存于活性锰含量较高的酸性土壤中,产生了环境适应性,逐渐进化出对锰的抗性。此外,Cg 04和Pt 715不分泌乙酸,但分泌草酸的速率随锰质量浓度的增加而提高;Sl 13能分泌乙酸,在锰质量浓度较高时,分泌草酸的速率显著降低,说明分泌草酸络合锰可能不是外生菌根真菌抗锰的唯一生化途径。Pt 715和Sl 13的氮、磷、钾吸收量显著高于Cg 04。在培养基中添加锰尤其是较高质量浓度的锰（800 mg/L）,Pt 715和Sl 13吸收养分的降幅显著低于Cg 04（除氮外）,降幅比Cg 04低20.28%～15.44%（磷）和51.20%～27.27%（钾）。在锰胁迫条件下,菌丝保持较强的养分吸收能力有益于细胞的健康,增强其抗锰能力,对于提高寄主植物的抗锰能力也可能有积极意义。      

Stomatal opening: role of potassium uptake by guard cells

Stomata in isolated epidermal strips open in response to light plus air free of carbon dioxide when the strips are floated on potassium chloride solutions of low concentrations. This opening depends on the stimulation of active accumulation of potassium in quantities sufficient to account for the observed changes in solute potential of the guard cells.     

Amino acid homology between the encephalitogenic site of myelin basic protein and virus: mechanism for autoimmunity

Amino acid sequence homology was found between viral and host encephalitogenic protein. Immune responses were then generated in rabbits by using the viral peptide that cross-reacts with the self protein. Mononuclear cell infiltration was observed in the central nervous systems of animals immunized with the viral peptide. Myelin basic protein (MBP) is a host protein whose encephalitogenic site of ten amino acids induces experimental allergic encephalomyelitis. By computer analysis, hepatitis B virus polymerase (HBVP) was found to share six consecutive amino acids with the encephalitogenic site of rabbit MBP. Rabbits given injections of a selected eight- or ten-amino acid peptide from HBVP made antibody that reacted with the predetermined sequences of HBVP and also with native MBP. Peripheral blood mononuclear cells from the immunized rabbits proliferated when incubated with either MBP or HBVP. Central nervous system tissue taken from these rabbits had a histologic picture reminiscent of experimental allergic encephalomyelitis. Thus, viral infection may trigger the production of antibodies and mononuclear cells that cross-react with self proteins by a mechanism termed molecular mimicry. Tissue injury from the resultant autoallergic event can take place in the absence of the infectious virus that initiated the immune response.     

Actinomycin D: uptake by sea urchin eggs and embryos

Actinomycin D is excluded from unfertilized eggs and developing embryos of the sea urchin Arbacia punctulata until the blastula hatches. The rate of uptake of actinomycin D by embryos doubles as development progresses after hatching to the gastrula stage.     

Relative humidity: important modifier of pollutant uptake by plants

Laboratory measurements of foliar uptake of sulfur dioxide and ozone by red kidney beans demonstrated a strong effect of relative humidity on internal pollutant dose. Foliar uptake was enhanced two- to threefold for sulfur dioxide and three- to fourfold for ozone by an increase in relative humidity from 35 to 75 percent. For the same exposure concentration, vegetation growing in humid areas (such as the eastern United States) may experience a significantly greater internal flux of pollutants than that in more arid regions.