Analysis of the electron transfer from Pheo to QA in PS II membrane fragments from spinach by time resolved 325 nm absorption changes in the picosecond domain

Absorption changes at 325 nm (delta A325) induced by 15 ps laser flashes (lambda = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (PI QA-) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 x 10(14) photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (delta A closed 325) from those in open RCs (delta A open 325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo- with a time constant of about 350 +/- 100 ps.     

On the mechanism of cytochrome oxidation in bacterial photosynthesis Quantum tunnelling effects revisited

We propose that the unique temperature dependence of the Chance-De Vault cytochrome oxidation reaction in Chromatium is not due to a transition from low-temperature nuclear tunnelling to a high-temperature activated electron transfer (ET), but rather originates from two parallel ET processes from two distinct low-potential cytochromes to the bacteriochlorophyll dimer cation. These involve a slow activationless process, which dominates at low temperatures (T 120 K) and an activated process, which is practically exclusive at high temperatures. This conjecture provides plausible nuclear and electronic coupling terms and structural data for the two cytochrome oxidation reactions.     

A nonconjugative mobilizable broad host range plasmid of Acinetobacter sp. that determines HgCl2 resistance

Summary HgCl₂-resistant strains of Acinetobacter sp. obtained from the soil at the Khaidarkan mercury mine (Kirghiz SSR) were found to contain, apart from large plasmids (60 kb), a small plasmid (7.5 kb) designated pKL1. It was established by conjugative crosses and transformation that pKL1 is a broad host range mobilizable plasmid and that it carries the Hg^r determinant. The restriction map of pKL1 was constructed; the site of the Hg^r determinant and the regions essential to replication were localized. A comparison of these results with earlier data suggests that microorganisms belonging to one microbiocenosis may carry Hg^r determinants on plasmids with highly different structures and properties.Deceased on July 16, 1985     

Competition between siratro and kleingrass for15N labelled mineralized nitrogen

Summary Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from a legume to a grass. A plant growth medium was enriched with¹⁵N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown in pure stand and in mixtures. When grown in 50∶50 mixture the grass obtained 59% of the labelled N and the legume obtained 41%. The grass produced nearly as much root mass as the legume even though biomass of the shoots were less than half that of the legume. Reducing the proportion of either plant species in the mixture reduced the proportion of the mineralized N absorbed by that species. The shoots of the grass were significantly more enriched (1.166 atom%¹⁵N excess) than the roots (1.036). The grass received 12% of its N as biologically fixed N from the legume.     

Sedimentary records of accelerated nutrient loading in Florida lakes

Transfer functions relating trophic state (Carlson's TSI_{chlorophyll-a}) to present day accumulation rate of (1) nutrients, (2) cations, and (3) organic sediment, are computed using Binford's ²¹⁰Pb-dilution method. As computed from surficial sediments of 27 lakes, former trophic states are reconstructed for recent (²¹⁰Pb-dated) sedimentary histories of 14 lakes. Of the three kinds of models potentially available, model (3) (TSI vs. organic accumulation) is the weakest statistically, and may be unduly influenced by exceptional deposition and/or preservation of allochthonous organic matter. At present, however, it is the only model applicable to all 14 of the histories tested. Results are encouraging in that model accurately predicts observed TSI's in several mesotrophic and eutrophic lakes. Clearly significant increases (accelerations) are inferred only for a of the most eutrophic lakes of the set, while the model consistently overpredicts TSI's of the 7 most oligotrophic lakes. As Whitmore's diatom-assemblage index is a better predictor of TSI than is model (3) in the one eutrophic lake in which it has been tested, we expect more persuasive results when models (1) and (2) can be tested within a more complete set of analytical data. We were surprised to find 3 severely disturbed lakes among the 12 that show little or no acceleration in rate of eutrophication in recent decades, but we defer attempts at explanation until former nutrient loading can be tested by model (1).     

呼吸链底物和抑制剂对线粒体内膜流动性的影响

用DPH和ANS标记大鼠肝线粒体内膜,以稳态荧光偏振法,研究了呼吸链底物和抑制剂对内膜流动性的影响。1.苹果酸+谷氨酸、琥珀酸分别为底物,均能引起内膜流动性增加。2.琥珀酸对含心磷脂的脂质体的膜流动性无影响。3.在鱼藤酮存在的条件下,苹果酸+谷氨酸对内膜流动性的增加作用消失,但琥珀酸的作用仍然存在。有氰化钾时则琥珀酸的作用消失。4.不论外加底物存在与否,鱼藤酮使内膜的流动性下降,而氰化钾则使之增加。抗霉素A亦可使内膜的流动性增加。上述结果表明:线粒体内膜流动性与其功能密切相关。电子沿呼吸链传递使线粒体内膜流动性增加,这种变化可能与呼吸链成分的氧化还原态有关。     

Chromosome-mediated transfer of murine alleles for hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and ouabain resistance into human cell lines

Genetic drug-resistance markers were transferred via purified metaphase chromosomes from mouse L cells into the human fibrosarcoma line HT1080 and HeLa S3 cells. Interspecific chromosome-mediated transfer of hypoxanthine-guanine phosphoribosyl transferase (HGPRT; EC 2.4.2.8) from mouse L cells into HGPRT^– HT1080 cells occurred at a frequency of approximately 1×10^–7. The presence of the mouse allele for HGPRT in transferent isolates was confirmed by isoelectric focusing. Transfer of ouabain resistance from mouse L cells to HT1080 and HeLa S3 cells occurred at an average frequency of approximately 4×10^–7. Expression of the mouse trait in transferent isolates was confirmed by their ability to withstand doses of ouabain which would be lethal to spontaneous ouabain-resistant mutants of the human cells but not to mouse L cells. Ouabain-resistant transferents of human cells showed 10⁴- to >10⁵-fold enhanced drug resistance, characteristic of either wild-type or mutant alleles, respectively, from ouabain-resistant donor L cells. Unstable expression of the transferred phenotypes in the absence of selection was seen in some isolates, but expression was lost at slow rates.This work was supported by National Institutes of Health Grant GM30383/21665 to RMB, Core Grants CA14051 to S. E. Luria and CA24538 to E. Mihich, and institutional predoctoral Training Grant GM07287.     

Catalysis by heteropentalenes of electron transfer to oxygen from ferredoxin-NADP oxidoreductase reduced by NADPH

A range of heteropentalene and bipyridinium compounds have been tested as catalysts of electron transfer to oxygen from spinach ferredoxin-NADP⁺ oxidoreductase reduced by NADPH. For a particular class of compound, the rate of oxygen reduction increased with increasing midpoint potential of the compound under conditions in which reduction of the compound was rate-limiting. Compounds with similar midpoint potentials from different structural classes showed marked differences in rate, attributed to specificity in the interaction with ferredoxin-NADP⁺ oxidoreductase.     

Ecology of nematophagous fungi: vertical distribution in a deciduous woodland

Summary The distribution of nematophagous fungi in soil collected from a deciduous woodland is compared to various biotic and abiotic soil factors. The microfungi are isolated at all depths down to a maximum of 35 cm. Predators forming constricting rings, adhesive branches and adhesive knobs are restricted to the upper litter and humus layers. The net forming predators and endoparasites are isolated at all depths, although they are significantly more abundant in the lower mineral rich soils. A much greater species diversity of nematophagous fungi is recorded in the upper organic zones.Preliminary soil analysis indicates thatCephalosporium balanoides is independent of all soil variables, while predators able to form traps spontaneously are restricted to the organic soils which are rich in nematodes. Non-spontaneous trap forming predators, which are excellent saprophytes, are isolated from the deeper soils which are low in nutrients. The ecological significance of these results is discussed.