Cysteamine: differential x-ray protective effect on Chinese hamster cells during the cell cycle

Cysteamine present during x-irradiation protects synchronized Chinese hamster cells in culture against lethal damage at all stages of the cell cycle. The effect is greatest for cells irradiated at sensitive stages such as G(1) and least for resistant cells; for example, late S (dose-modifying factors 4.2 and 2.7, respectively). The effect of 50 millimolar cysteamine is to render almost invariant the normally variant x-ray age response for lethality. This suggests that there are two components of x-ray damage, only one of which is age dependent, and it is against this component that cysteamine protects the cell. Cystamine, however, has no protective effect upon these cells at any stage of the cell cycle.     

Bright coherent ultrahigh harmonics in the keV x-ray regime from mid-infrared femtosecond lasers

High-harmonic generation (HHG) traditionally combines ~100 near-infrared laser photons to generate bright, phase-matched, extreme ultraviolet beams when the emission from many atoms adds constructively. Here, we show that by guiding a mid-infrared femtosecond laser in a high-pressure gas, ultrahigh harmonics can be generated, up to orders greater than 5000, that emerge as a bright supercontinuum that spans the entire electromagnetic spectrum from the ultraviolet to more than 1.6 kilo-electron volts, allowing, in principle, the generation of pulses as short as 2.5 attoseconds. The multiatmosphere gas pressures required for bright, phase-matched emission also support laser beam self-confinement, further enhancing the x-ray yield. Finally, the x-ray beam exhibits high spatial coherence, even though at high gas density the recolliding electrons responsible for HHG encounter other atoms during the emission process.     

Structural correlation between esterase and protease activities on trypsin

It is tentatively concluded from ultraviolet and x-ray studies that the two tryptic activities are mediated by overlapping "enzymatic sites." Crucial to this conclusion were studies of the factors which can modify the measured inactivation rates. The data are interpreted in the light of postulated mechanisms of inactivation.     

木霉菌素产生菌的诱变育种

[目的]筛选高产木霉菌素菌株,提高木霉菌素产量。[方法]以从枸骨中分离到的产木霉菌素的内生真菌———哈茨木霉为出发菌株,进行紫外线二次复合诱变处理,将筛选出的突变菌株连续转接5代,测定其遗传稳定性。[结果]随着照射时间的延长,哈茨木霉的致死率增大,选取致死率为88.1%的紫外线照射45 s作为最适处理剂量进行诱变育种。经过2次诱变的菌株的产孢时间提前,长出的菌落更为致密。经过初筛和复筛,最终获得1株高产突变株UV-5-3,其产抗生素的水平最高,为164.75μg/m l,比初次诱变筛选获得的突变株UV-3-1提高了56.77%,是出发菌株的2.3倍。传代试验表明,突变株UV-5-3的高产性能遗传特性稳定。[结论]利用紫外线二次复合诱变处理哈茨木霉可以获得高产木霉菌素菌株。     

Steering attosecond electron wave packets with light

Photoelectrons excited by extreme ultraviolet or x-ray photons in the presence of a strong laser field generally suffer a spread of their energies due to the absorption and emission of laser photons. We demonstrate that if the emitted electron wave packet is temporally confined to a small fraction of the oscillation period of the interacting light wave, its energy spectrum can be up- or downshifted by many times the laser photon energy without substantial broadening. The light wave can accelerate or decelerate the electron's drift velocity, i.e., steer the electron wave packet like a classical particle. This capability strictly relies on a sub-femtosecond duration of the ionizing x-ray pulse and on its timing to the phase of the light wave with a similar accuracy, offering a simple and potentially single-shot diagnostic tool for attosecond pump-probe spectroscopy.     

Antigenic similarity between cells transformed by ultraviolet radiation in vitro and in vivo

Cells of the 10T 1/2 mouse fibroblast line transformed in vitro by ultraviolet radiation are antigenically similar to those from skin cancers produced in mice by repeated exposure to ultraviolet radiation. Both types of tumor cells grew preferentially in ultraviolet-irradiated syngeneic mice relative to untreated animals, and both were recognized by ultraviolet radiation-induced tumor-specific suppressor lymphocytes. These properties were not shared by 10T 1/2 cells transformed in vitro by x-rays or 3-methylcholanthrene.     

Time-resolved x-ray diffraction of biological materials

Instrumental and specimen considerations pertinent to performing time-resolved x-ray diffraction on biological materials are discussed. Existing synchrotron x-ray sources, in conjunction with integrating x-ray detectors, have made millisecond diffraction experiments feasible; exposure times several orders of magnitude shorter than this will be possible with synchrotron sources now on the drawing boards. Experience gained from time-resolved studies together with order-of-magnitude estimates of specimen requirements can be used to determine the instrumental capabilities needed for various time-resolved experiments. Existing instrumental capabilities and methods of dealing with time-resolved specimens are reviewed.     

ROSAT Observations of X-ray Emissions from Jupiter During the Impact of Comet Shoemaker-Levy 9

R?ntgensatellit (ROSAT) observations made shortly before and during the collision of comet Shoemaker-Levy 9 with Jupiter show enhanced x-ray emissions from the planet's northern high latitudes. These emissions, which occur at System III longitudes where intensity enhancements have previously been observed in Jupiter's ultraviolet aurora, appear to be associated with the comet fragment impacts in Jupiter's southern hemisphere and may represent brightenings of the jovian x-ray aurora caused either by the fragment impacts themselves or by the passage of the fragments and associated dust clouds through Jupiter's inner magnetosphere.     

Multiphoton ionization of atoms

Studies of multiphoton ionization of atoms have revealed several unexpected characteristics. The confluence of the experimental evidence leads to the hypothesis that the basic character of the atomic response involves highly organized, coherent motions of entire atomic shells. The important regime, for which the radiative field strength is greater than an atomic unit (e/a(2)(0)), can be viewed in approximate correspondence with the physics of fast (approximately 10 MeV per atomic mass unit) atom-atom scattering. This physical picture provides a basis for the expectation that stimulated emission in the x-ray range can be produced by direct, highly nonlinear coupling of ultraviolet radiation to atoms.     

Effects of solar flares on the ionosphere of Mars

All planetary atmospheres respond to the enhanced x-rays and ultraviolet (UV) light emitted from the Sun during a flare. Yet only on Earth are observations so continuous that the consequences of these essentially unpredictable events can be measured reliably. Here, we report observations of solar flares, causing up to 200% enhancements to the ionosphere of Mars, as recorded by the Mars Global Surveyor in April 2001. Modeling the altitude dependence of these effects requires that relative enhancements in the soft x-ray fluxes far exceed those in the UV.     

Motor responses of moths to low-intensity x-ray exposure

A brief burst of x-rays elicited flight activity in moths placed in a darkened x-ray exposure room. Wing-beat activity was recorded as an index of this behavior. Wing-beat activity could be initiated in resting moths or amplitude augmented in active moths by x-ray dose rates of 0.01 to 1.5 roentgens per second, with a latency of less than 1 second after onset of exposure.     

Immunologic inhibition of ultraviolet radiation-induced tumor suppressor cell activity

Long-term exposure of C3H mice to ultraviolet radiation resulted in the formation of suppressor T cells that recognize ultraviolet radiation-induced regressor skin cancers as a class before the appearance of overt tumors. Administration of monoclonal antibodies to the product of the I-Jk subregion of the major histocompatibility complex or low doses of cyclophosphamide in vivo inhibited the development or activity of these cells. This activity of the monoclonal antibody was eliminated by adsorption on B10.BR (I-Jk) but not B10.D2 (I-Jd) splenocytes. These findings provide evidence that elements expressing the I-J determinant are important in regulating the host response prior to the overt development of ultraviolet radiation-induced skin cancers and suggest novel therapeutic approaches to malignancies or other diseases involving suppressor T cells in their pathogenesis.     

Deep UV photochemistry of chemisorbed monolayers: patterned coplanar molecular assemblies

Deep ultraviolet (UV) irradiation is shown to modify organosilane self-assembled monolayer (SAM) films by a photocleavage mechanism, which renders the surface amenable to further SAM modification. Patterned UV exposure creates alternating regions of intact SAM film and hydrophilic, reactive sites. The exposed regions can undergo a second chemisorption reaction to produce an assembly of SAMs in the same molecular plane with similar substrate attachment chemistry. The UV-patterned films are used as a template for selective buildup of fluorophores, metals, and biological cells.     

DNA damage-induced replication fork regression and processing in Escherichia coli

DNA lesions that block replication are a primary cause of rearrangements, mutations, and lethality in all cells. After ultraviolet (UV)-induced DNA damage in Escherichia coli, replication recovery requires RecA and several other recF pathway proteins. To characterize the mechanism by which lesion-blocked replication forks recover, we used two-dimensional agarose gel electrophoresis to show that replication-blocking DNA lesions induce a transient reversal of the replication fork in vivo. The reversed replication fork intermediate is stabilized by RecA and RecF and is degraded by the RecQ-RecJ helicase-nuclease when these proteins are absent. We propose that fork regression allows repair enzymes to gain access to the replication-blocking lesion, allowing processive replication to resume once the blocking lesion is removed.     

Possible consequences of nearby supernova explosions for atmospheric ozone and terrestrial life

Hard x-ray pulses or increased cosmic radiation originating in nearby supernova explosions may be capable of temporarily removing most of the earth's atmospheric ozone cover even when direct radiation effects at the earth's surface are negligible. Consequently, terrestrial life may be subject to relatively huge solar ultraviolet fluxes every few hundred million years.     

二甲亚砜对黑曲霉孢子的紫外线抗性影响

为了探索黑曲霉(Aspergillus niger)孢子黑色素的抗紫外线功能,用不同浓度的黑色素抑制剂二甲亚砜(DMSO)处理A.niger,利用棉兰染液来确定孢子黑色素着色时间,用紫外灯管照射来观察孢子对紫外线的抗性,用称湿质量的方法来测定无黑色素的孢子在液体培养基中的生长状况.结果表明:DMSO浓度在0.5%～1%范围内,A.niger的生长不受影响,但黑色素生成被抑制.黑色素在查氏培养基的着色时间为72h左右.在紫外线照射1h后,A.niger存活率呈现下降趋势.无黑色素的A.niger孢子在液体培养基中生长周期缩短.因此认为,A.niger孢子黑色素对紫外线有较好的抵抗作用.     

紫外线照射对绿藻Scenedesmus dimorphus生长繁殖和叶绿素含量的影响

[目的]探讨太阳紫外线辐射增强与温室效应之间的关系。[方法]对盛有绿藻细胞悬液的培养皿用紫外灯照射0、20、40、60、80、100、120 s,研究紫外线照射对绿藻生长繁殖和叶绿素含量的影响。[结果]低剂量紫外线(20~60 s)照射对单细胞绿藻的分裂有一定的刺激作用,促进了绿藻细胞的生长。当紫外线照射时间延长至80 s以上时,绿藻的细胞密度急剧减少。低剂量紫外线(20~80 s)照射对绿藻叶绿素含量的影响不明显,较高剂量紫外线(100 s以上)照射显著降低了绿藻的叶绿素含量。[结论]太阳紫外线辐射增强可直接影响藻类的生长繁殖和叶绿素含量,间接影响其光合效率,从而增强了温室效应。     

高产纤维素酶的黑曲霉菌种的选育

[目的]为纤维素的进一步开发利用奠定理论基础。[方法]选取菌落直径较大的黑霉菌株W1作为出发菌株进行紫外线诱变,检测诱变菌株在不同发酵时间的纤维素酶活力。[结果]黑曲霉W1经紫外线诱变10 min达到92%致死率。在试验检测的108 h范围内,随着培养时间在一定范围内延长,出发菌株W1菌株和从中筛选出的高产纤维素酶菌株NW1的酶活均有不同程度的提高,NW1在28℃100r/min培养84 h后酶活最高达到1.515 U/ml,W1培养84 h酶活达到0.958 U/ml,较出发菌株W1提高了1.58倍。之后2者的酶活都随着培养时间的延长稍有降低。利用0.1%刚果红染液初步检测诱变10 min的黑曲霉分泌纤维素酶情况,结果发现诱变菌株NW1分泌纤维素酶能力最强。[结论]黑曲霉诱变菌株具有较强的分泌纤维素酶的能力。     

壳斗科等树种种子射线造影技术研究

本文应用软x射线仪对壳斗科等20个树种种子进行衬比造影和直接造影技术的研究,找出各树种种子不同焦片距(300mm和200mm)、不同感光材料(x光胶片、普通胶片、相纸)的最适电压、电流和曝光时间,以及最适衬比剂、衬比浓度和衬比时间,供生产科研等种子检验部门参考。     

纤维素酶高产菌株的诱变选育

[目的]选择有效的方法选育高产纤维素酶菌种。[方法]利用黑曲霉为出发菌株,经过紫外线和亚硝酸复合诱变,选育出酶活力高的突变株进行培养并测定其酶活。[结果]在单因子诱变中,紫外线效果明显优于亚硝酸,致死率70%~80%的诱变剂量比较理想。复合诱变比单因子诱变效果好,产酶能力得到提高,而且菌落生长速度也加快,在多次传代试验中,菌株的性状也比较稳定。出发菌株通过紫外线(15 W,照射距离30 cm左右,照射时间8 min)和亚硝酸(0.1 mol/L的NaNO3处理5 min)的复合诱变,复筛得到纤维素酶高产菌株,纤维素酶活力提高了61.10%,滤纸酶活力提高了64.01%。[结论]通过紫外线和亚硝酸复合诱变能选育出有较高纤维素酶活力的菌株。