This article describes an experimental program developed to investigate the potential for using hydrocarbon‐contaminated soils as a fine aggregate replacement in concrete. Five different contaminated soil types with a total petroleum hydrocarbon content of less than 1% were investigated. For each soil type, three concrete mixtures were obtained by replacing sand with contaminated soils (10, 20, and 40% replacement ratio). The resulting concrete was tested for setting times, compression strength, flexural strength, durability, and teachability of benzene to water.
The results indicate that the addition of hydrocarbon‐contaminated soil adversely affects the strength of concrete. The strength reduction at each soil replacement level depends on contamination concentration, contaminant type, and soil type. The durability of the tested concrete is comparable to normal concrete. For all five soils at a 40% replacement ratio, the leachability of benzene was nondetectable after 24 h and after 10 d. After testing the leachability of artificially contaminated soils (0.5 and 3% neat benzene contamination) for 24 h, it was found that the leaching of benzene increases with the percentage of contamination. However, the fraction of benzene that leached was about 95% lower than the values for loose soils. 相似文献
The activity of peroxidases in the proximal part of the flower peduncle of rose cv. Nubia was promoted by exogenous application of auxin but not by gibberellin or cytokinin. In cv. Mercedes the activity was promoted also by gibberellin and cytokinin. In the distal parts of the peduncles of both cultivars, peroxidase activity was not affected by any of the applied growth regulators. In young flowers of cv. Nubia the protein content of the penduncles was affected only by cytokinin, and in aged flowers only by auxin, while in Mercedes peduncles the content of protein was not affected by any of the applied growth regulators. The specific activity of peroxidases was promoted by auxin in peduncles of Nubia and by both auxin and cytokinin in peduncles of Mercedes flowers. 相似文献
The nuclear genome of Chlamydomonas reinhardtii encodes a dozen hemoglobins of the truncated lineage. Four of these, named THB1–4, contain a single ~130-residue globin unit. THB1, which is cytoplasmic and capable of nitric oxide dioxygenation activity, uses a histidine and a lysine as axial ligands to the heme iron. In the present report, we compared THB2, THB3, and THB4 to THB1 to gain structural and functional insights into algal globins.
Methods
We inspected properties of the globin domains prepared by recombinant means through site-directed mutagenesis, electronic absorption, CD, and NMR spectroscopies, and X-ray crystallography.
Results
Recombinant THB3, which lacks the proximal histidine but has a distal histidine, binds heme weakly. NMR data demonstrate that the recombinant domains of THB2 and THB4 coordinate the ferrous heme iron with the proximal histidine and a lysine from the distal helix. An X-ray structure of ferric THB4 confirms lysine coordination. THB1, THB2, and THB4 have reduction potentials between ?65 and ?100 mV, are capable of nitric oxide dioxygenation, are reduced at different rates by the diaphorase domain of C. reinhardtii nitrate reductase, and show different response to peroxide treatment.
Conclusions
Three single-domain C. reinhardtii hemoglobins use lysine as a distal heme ligand in both Fe(III) and Fe(II) oxidation states. This common feature is likely related to enzymatic activity in the management of reactive oxygen species.
General significance
Primary structure analysis of hemoglobins has limited power in the prediction of heme ligation. Experimental determination reveals variations in this essential property across the superfamily. 相似文献
Summary Relaxation times of 13C carbons of uniformly 13C/15N-enriched probes have been investigated. The relaxation behaviour was analyzed in terms of a multispin system. Pulse sequences for the determination of T1, T2 and the heteronuclear NOE of 13C in uniformly 13C/15N-enriched ribonuclease T1 are presented. The experiments performed in order to obtain T1 and the heteronuclear NOE were similar to those of the corresponding 15N experiments published previously. The determination of T2 for the C-carbon in a completely labeled protein is more complicated, since the magnetization transfer during the T2 evolution period owing to the scalar coupling of C–C must be suppressed. Various different pulse sequences for the T2 evolution period were simulated in order to optimize the bandwidth for which reliable T2 relaxation times can be obtained. A proof for the quality of these pulse sequences is given by fitting the intensity decay of individual 1H–13C cross peaks, in a series of (1H, 13C)-ct-HSQC spectra with a modified CPMG sequence as well as a T1p sequence for the transverse relaxation time, to a single exponential using a simplex algorithm. 相似文献
Previously considered as toxin-free, the Baja California Peninsula has witnessed several toxic algal blooms during the past
three years. Apparently these ‘red-tide’ phenomena's outbreaks are not linked to any human related activity. This may just
reflect better detection and training. Such events may be periodical and natural rather than induced. The most common types
of marine toxins have been detected along the coast of the Peninsula and neighboring waters by mouse bioassay and chromatographic
techniques. These are: Tetrodotoxin (TTX), Amnesic Shellfish Poison (ASP), Paralytic Shellfish Poisons (PSP), Diarrhetic Shellfish
Poisons (DSP) and even Ciguatera (CFP), which are related to the presence of organisms of Prorocentrum sp. and Alexandrium
sp. groups, and the diatom Pseudonitzschia sp. among others. There are also some indications about different kinds of TTX
in the puffer fish of the region, and reasons to believe that we are facing a quite different pattern in toxic components,
since PSP toxic potency (defined as the number of mouse units per gram(MU/g)of shellfish meat) is very high in spite of low
dinoflagellates cell density registered. The ecological and social impact of the above has been considerable, with mass deaths
of shellfish, seagulls, dolphins and turtles, and even some human casualties. The locally registered toxicity records: PSP
found in one single fanshell reaches to 23 000 MU/100 g of tissue as determined by the mouse bioassay and, on a different
event, two persons killed after ingesting puffer fish fillet. The largest reservoir of commercial marine organisms in Mexico
is precisely the Northwest coast of the country and important plans for building large harbors and develop aquaculture areas
are in progress. Therefore, a monitoring program is essential for an adequate management of such resources. Considering the
large extension of the Peninsula (about1600 km)and, at this time, the lack of efficient communication means and scarce population,
the implementation of such monitoring programs presents a big challenge.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
A putative natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae) from southern Italy, formerly known asO. alata, was characterized both on morphological and molecular grounds in order to confirm its hybrid status and to trace its maternal lineage. The morphological characters of the putative hybrid showed intermediacy between those of the parent species, and restriction fragment length polymorphism (RFLP) analysis of a region of the nuclear ribosomal DNA confirmed its hybrid origin. Chloroplast DNA RFLP analysis indicated thatO. morio provided the maternal genome. 相似文献
Mn, Fe, Cu, and Cd concentrations are reported for Lake Vanda, a closed-basin, meromictic, Antarctic lake and for its single major inflow, the Onyx River. Trace metal distributions in the upper lake and annual metal fluxes from the Onyx River were used to estimate chemical residence times in the mixed zone above the chemocline. Residence times, based on total metal loads, were 9.4 years for Mn; 1.4 years for iron; 174 years for copper; and 82 years for cadmium. Controls on the steady state concentrations of metals in this system are likely to include: particle settling of Fe and Mn; scavenging of minor elements on metal oxide surfaces; sulfide precipitation from the anoxic brine; and possibly uptake of metals on the surface of benthic algal mats. Model calculations show that metal removal by sinking phytoplankton can account for only a small fraction of the annual loss. 相似文献