Adenosine 3',5'-monophosphate-dependent protein kinase from brain

Adenosine 3',5'-monophosphate at a concentration of 5 x 10(-7) mole per liter causes a 400 percent increase in the rate of phosphorylation of histone catalyzed by a partially purified enzyme preparation from rabbit brain. The data provide the first direct evidence of a biochemical action of adenosine 3',5'-monophosphate in the brain.     

Gibberellic acid: a growth factor in the unicellular alga Gymnodinium breve

Gibberellic acid stimulates growth in the unicellular alga Gymnodinium breve (dinoflagellate). The maximum effect was obtained with 10(-7) molar gibberellic acid, whereas concentrations greater than 5 x 10(-7) mole per liter were inhibitory. The effect of the compound is observed as a marked shortening of the lag period, which is normally 6 to 8 days after innoculation.     

Bradykinin inhibition by butylated hydroxyanisole

Concentrations of butylated hydroxyanisole as low as 8 x 10(-9) mole per liter can inhibit detectably the contraction of smooth muscle elicited by bradykinin. The mechanism of the inhibitory effect of this food grade anti-oxidant is apparently complex, and the effect is only partially reversible.     

Saxitoxin and tetrodotoxin: comparison of nerve blocking mechanism

Saxitoxin at concentrations of 3 x 10(-8) to 3 x 10(-7) mole per liter blocks the conduction of lobster giant axon with no change in resting potential. Recovery of washed axons is faster in those that had been treated with saxitoxin than it is in those that were treated with tetrodotoxin. Peak transient increase in nerve membrane conductance is selectively blocked by saxitoxin with no change in late steady-state increase in conductance. The major mechanism of saxitoxin blockage is the same that of tetrodotoxin blockage.     

The Density of Hydrous Magmatic Liquids

Density measurements on several hydrous (相似文献   

Cypridina bioluminescence: light-emitting oxyluciferin-luciferase complex

Fluorescence of Cypridina oxyluciferin is greatly enhanced when it is bound to luciferase; the spectrum is thereby shifted, so that it corresponds precisely to the emission spectrum characteristic of the bioluminescentoxidation of luciferin. Thus the oxyluciferin-luciferase complex is the lightemitter. The binding is equimolar, with dissociation constant K(D) equal to 3x 10(-7) mole per liter. The molecular weight of the luciferase, according to three different methods, is between 52,000 and 57,000; molecular activities of luciferase for the bioluminescence reaction and for the hydrolysis of oxy-luciferin are 1600 and 2 per minute, respectively.     

Potassium ion specific electrode with high selectivity for potassium over sodium

A new potassium electrode, made from valinomycin, which uses commercially available electrode configurations, responds to potassium ion concentrations from 1 mole per liter to below 10(-6) mole per liter. It is highly selective for potassium ion over sodium ion and divalent ions and can be used for the direct determination of potassium ion in human serumn. No significant complexing of potassiium appears to occur in normal seruin.     

Free-radical oxidants in natural waters

Photooxidation of cumene (isopropylbenzene) and pyridine in dilute solution in natural waters gives products characteristic of reactions with alkylperoxy (RO(2).) and hydroxyl (HO.) radicals. On the basis of the rates of formation of the products, the average concentrations of RO(2). and HO. are estimated to be about 10(-9) and 10(-17) mole per liter, respectively. The concentration of RO(2). is large enough that, for some classes of reactive chemicals, oxidation can be an important process in natural waters.     

A polymorphism within the G6PC2 gene is associated with fasting plasma glucose levels

Several studies have shown that healthy individuals with fasting plasma glucose (FPG) levels at the high end of the normal range have an increased risk of mortality. To identify genetic determinants that contribute to interindividual variation in FPG, we tested 392,935 single-nucleotide polymorphisms (SNPs) in 654 normoglycemic participants for association with FPG, and we replicated the most strongly associated SNP (rs560887, P = 4 x 10(-7)) in 9353 participants. SNP rs560887 maps to intron 3 of the G6PC2 gene, which encodes glucose-6-phosphatase catalytic subunit-related protein (also known as IGRP), a protein selectively expressed in pancreatic islets. This SNP was associated with FPG (linear regression coefficient beta = -0.06 millimoles per liter per A allele, combined P = 4 x 10(-23)) and with pancreatic beta cell function (Homa-B model, combined P = 3 x 10(-13)) in three populations; however, it was not associated with type 2 diabetes risk. We speculate that G6PC2 regulates FPG by modulating the set point for glucose-stimulated insulin secretion in pancreatic beta cells.     

Aluminum-26 and beryllium-10 in greenland ice

Activities of beryllium-10 and aluminum-26 dissolved in 200-year-old Greenland ice were found to be 18.4 (+ 8.4, - 4.8) x 10(-6) and 3.2 +/- 0.9 x 10(-7) disintegration per minute per liter, respectively. From these values and the precipitation rate (30 milliliters of water per square centimeter per year), the production rates of these isotopes are calculated to be 3.6 (+ 1.6, - 0.9) x 10(-2) and 1.7 +/- 0.5 x 10(-4) atom per second * square centimeter. These rates agree with the rates calculated for the production of these isotopes by cosmic rays in the atmosphere. Probably all the Al(26) in the ice is accounted for by such atmospheric production; however, an upper limit for the influx of cosmic dust bearing aluminum-26 is calculated at 3.2 x 10(5) tons per year for Earth. Only upper limits could be found for Al(26) and Be(10) in the undissolved particulate matter in the ice; their addition to the activities in the dissolved material leaves our conclusions unchanged.     

Reaction of hydrated electrons with ferricytochrome C

The reaction of ferricytochrome c with hydrated electrons produced at pH 6.8 by radiolysis with electron pulses lasting 50 to 1000 nanoseconds has a specific rate constant of 5.5 x 10(10) liter mole(-1) sec(-1) for the formation of the primary adduct. By using appropriate wavelengths, another fast, consecutive process was demonstrated, with the pure first order rate constant 1.0 x 10(5) sec(-1). Its characteristics agree with it being an intramolecular process within the enzyme. Approximately 50 percent of all electrons which add to ferricytochrome c end in forming ferrocytochrome c.     

Spherical bilayer vesicles of fullerene-based surfactants in water: a laser light scattering study

The low solubility of fullerenes in aqueous solution limits their applications in biology. By appropriate substitution, the fullerenes can be transformed into stabilized anions that are water soluble and can form large aggregated structures. A laser light scattering study of the association behavior of the potassium salt of pentaphenyl fullerene (Ph5C60K) in water revealed that the hydrocarbon anions Ph5C60- associate into bilayers, forming stable spherical vesicles with an average hydrodynamic radius and a radius of gyration of about 17 nanometers at a very low critical aggregation concentration of less than 10(-7) moles per liter. The average aggregation number of associated particles in these large spherical vesicles is about 1.2 x 10(4).     

Design and evolution of new catalytic activity with an existing protein scaffold

The design of enzymes with new functions and properties has long been a goal in protein engineering. Here, we report a strategy to change the catalytic activity of an existing protein scaffold. This was achieved by simultaneous incorporation and adjustment of functional elements through insertion, deletion, and substitution of several active site loops, followed by point mutations to fine-tune the activity. Using this approach, we were able to introduce beta-lactamase activity into the alphabeta/betaalpha metallohydrolase scaffold of glyoxalase II. The resulting enzyme, evMBL8 (evolved metallo beta-lactamase 8), completely lost its original activity and, instead, catalyzed the hydrolysis of cefotaxime with a (kcat/Km)app of 1.8 x 10(2) (mole/liter)(-1) second(-1), thus increasing resistance to Escherichia coli growth on cefotaxime by a factor of about 100.     

地塞米松与肝素对HL－60细胞增值和生物大分子合成的影响

用地塞米松（Ｄｅｘ）和肝素（Ｈｅｐ）Ｉｃ６０及Ｉｃ５０低一个剂量，对ＨＬ－６０细胞增殖、生长曲线和分裂指数均有明显的抑制作用，联合应用时抑制作用显著增强；对ＤＮＡ和蛋白质合成抑制作用大于ＲＮＡ，联合应用抑制作用均显著增强，提示两药抑制ＨＬ－６０细胞增殖、分裂和生长可能与它们抑制ＤＮＡ和蛋白质合成有关，亦与抑制ＲＮＡ合成有一定关系。     

平贝母体细胞胚胎发生早期核酸和蛋白质合成动态的研究

在长期平贝母(Frifiiavia ussuviensis Maxim)组织培养中,建立比较稳定的体细胞胚胎发生体系,应用放射性同位素~3H 的液体闪烁技术测得,体细胞胚 RNA、蛋白质和 DNA 合成分别在诱导培养第5,7,8b 达到高峰。组织细胞学观察表明,体细胞胚胎发生早期的核酸与蛋白质合成的变化与愈伤组织中细胞的胚性化和胚性细胞的增殖相关。     

Asbestiform amphibole minerals: detection and measurement of high concentrations in municipal water supplies

Ashestiform amphibole minerals, which have been demonstrated to be associated with human health problems, have been detected in substantial quantities in municipal water supplies taken from western Lake Superior Water. The total concentrationl of amphibole minerals in the Duluth, Minnesota, water supply, as measured by x-ray diffraction for daily samples of suspended solids averages 0.19 milligram per liter with large fluctuations due to seasonal and climatological effects on lake circulation. Electron microscopic examination of these water samples confirms the presence of asbestiform amphibole fibers. A conservatiue estimate of the fiber count for 1973 Duluth water supply samples is (1 to 30) x 10(6) amphibole fibers identifiable by electron diffraction per liter of water with a mass concentration of 1 to 30 micrograms per liter.     

Hemoglobin Kinetics of the Galapagos Rift Vent Tube Worm Riftia pachyptila Jones (Pogonophora; Vestimentifera)

Kinetics of the reactions of Riftia pachyptila hemoglobin with oxygen were followed spectrophotometrically by stopped-flow and laser flash photolysis techniques. The rate of oxygen dissociation increases eightfold over the range of 5 degrees to 20 degrees C (k = 2.2 sec(-1)at 10 degrees C). Oxygen recombination after flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0 degrees to 20 degrees C(k'fast = 7 x 10(6); k'slow = 1 x 16(6) liter mole (-1) sec(-1)). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of cooperativity requires that the conformational equilibrium constant L decrease by about 50-fold between 3 degrees and 15 degrees C.     

Electrical phenomena associated with the activity of the membrane-bound acetylcholinesterase

Treatment of isolated electroplax with physiological solutions supplemented with either 1 molar sodium chloride, 2 molar urea, or 2 molar sucrose renders the cell insensitive to carbamylcholine, phenyltrimethylammonium, or decamethonium even at high concentrations. The treated cells have a residual resting potential of -20 +/- 10 millivolts (negative inside) and are depolarized by acetylcholine at concentrations larger than 10(-3) mole per liter. This response is not affected by d-tubocurarine but is blocked by physostigmine, diisopropylphosphorofluoridate, or strong buffers and thus depends on the catalytic activity of the membrane-bound acetylcholinesterase.     

Radium-226 and radon-222: concentration in atlantic and pacific oceans

Measurements of radon-222 in seawater suggest the following. The radium-226 content of surface water in both the Atlantic and Pacific oceans is uniformly close to about 4 x 10(-14) gram per liter. The deep Pacific has a concentration of radium-226 that is four times higher and the deep Atlantic a concentration twice as high as that of the surface. These distribution profiles can be explained by the same particle-settling rate for radium-226 from surface to depth for the two oceans and by a threefold longer residence time of water in the deep Pacific than in the deep Atlantic. The vertical distribution of the deficiency of radon-222 in the surface water of the northwest Pacific Ocean suggests a coefficient of vertical eddy diffusion as high as 120 square centimeters per second and a gas-exchange rate for carbon dioxide in surface water between 14 and 60 moles per square meter per year. Vertical profiles of the excess of radon-222 in near-bottom water of the South Atlantic give coefficients of vertical eddy diffusion ranging from 1.5 to more than 50 square centimeters per second.     

Dormin (Abscisin II), inhibitor of plant DNA synthesis?

Dormin (abscisin II), inhibits growth of Lemna minor cultures. At 1 part per million (3.8x10(-6)M), the culture appears nearly completely dormant but can be revived readily by transferring it to fresh medium free of dormin. The cytokinin benzyladenine, but not auxin or gibberellin, will counteract the dormin effect. Quantitative restoration of normal growth by cytokinin, however, can be achieved only if the dormin concentration does not exceed a critical level. Separation, after phenol-detergent extraction, of nucleic acids on methylated albumin kieselguhr columns showed suppression of nucleic acid synthesis by dormin in all fractions. Inhibition of the synthesis of the DNA fraction seems to precede that of RNA. Cytokinins reverse the process. They promote synthesis of all nucleic acid fractions, but again DNA seems to lead. Further work on the interaction of dormin with growth-promoting hormones might be facilitated by adopting the Monod model of allosteric transition, with, for example, DNA polymerase as the protein, dormin as the inhibitor, and cytokinin or other growth promoters as activators.