Analysis of the ketosynthase-chain length factor heterodimer from the fredericamycin polyketide synthase

The pentadecaketide fredericamycin has the longest carbon chain backbone among polycyclic aromatic polyketide antibiotics whose biosynthetic genes have been sequenced. This backbone is synthesized by the bimodular fdm polyketide synthase (PKS). Here, we demonstrate that the bimodular fdm PKS as well as its elongation module alone synthesize undecaketides and dodecaketides. Thus, unlike other homologs, the fdm ketosynthase-chain length factor (KS-CLF) heterodimer does not exclusively control the backbone length of its natural product. Using sequence- and structure-based approaches, 48 CLF multiple mutants were engineered and analyzed. Unexpectedly, the I134F mutant was unable to turn over but could initiate and partially elongate the polyketide chain. This unprecedented mutant suggests that the KS-CLF heterodimer harbors an as yet uncharacterized chain termination mechanism. Together, our findings reveal fundamental mechanistic differences between the fdm PKS and its well-studied homologs.     

Macroscopic wall number analysis of single-walled, double-walled, and few-walled carbon nanotubes by X-ray diffraction

The layer number is of great importance for nanocarbon materials, such as carbon nanotubes (CNTs) and graphene. While simple optical methods exist to evaluate few-layer graphene, equivalent analysis for CNTs is limited to transmission electron microscopy. We present a simple macroscopic method based on the (002) X-ray diffraction peak to evaluate the average wall number of CNTs in the range from single- to few-walled. The key was the finding that the (002) peak could be decomposed into two basic components: the intertube structure (outer-wall contacts) and the intratube structure (concentric shells). Decomposition of the peaks revealed a linear relationship between the average wall number and the ratio of the intertube and intratube contributions to the (002) peak. Good agreement with CNTs having average wall numbers ranging from 1 to ～5 demonstrated this as a macroscopic method for average wall number analysis.     

Noninvasive imaging of cell death using an Hsp90 ligand

Cell death plays a central role in normal physiology and in disease. Common to apoptotic and necrotic cell death is the eventual loss of plasma membrane integrity. We have produced a small organoarsenical compound, 4-(N-(S-glutathionylacetyl)amino)phenylarsonous acid, that rapidly accumulates in the cytosol of dying cells coincident with loss of plasma membrane integrity. The compound is retained in the cytosol predominantly by covalent reaction with the 90 kDa heat shock protein (Hsp90), the most abundant molecular chaperone of the eukaryotic cytoplasm. The organoarsenical was tagged with either optical or radioisotope reporting groups to image cell death in cultured cells and in murine tumors ex vivo and in situ. Tumor cell death in mice was noninvasively imaged by SPECT/CT using an (111)In-tagged compound. This versatile compound should enable the imaging of cell death in most experimental settings.     

Photoelectron imaging spectroscopy and theoretical investigation of ZrSi

The photoelectron spectrum of ZrSi(-) has been measured at two different photon energies: 2.33 eV and 3.49 eV, providing electron binding energy and photoelectron angular distribution information. The obtained vertical detachment energy of ZrSi(-) is 1.584(14) eV. The neutral ground and excited state terms are assigned based on experimental and theoretical results. The ground state of ZrSi is tentatively assigned as a (3)Σ(+) state with a configuration of 1σ(2) 1π(4) 1δ(0) 2σ(1) 3σ(1). A low lying (3)Π(i) neutral excited state is identified to be 0.238 eV (1919 cm(-1)) above the ground state. The anion ground state is designated as a (2)Σ(+) state with a 1σ(2) 1π(4) 1δ(0) 2σ(2) 3σ(1) valence electron configuration. A Franck-Condon (FC) simulation of the photoelectron spectrum has been carried out. For the (3)Σ(+) ← (2)Σ(+) band, theoretically calculated bond lengths and frequencies are used in the FC calculation which give good agreement with experiment, while for the (3)Π(i) ← (2)Σ(+) band, the ZrSi bond length is estimated from the FC spectrum. Comparisons are made with previously published theoretical studies and inconsistencies are pointed out. To the best of our knowledge, this study provides the first spectroscopic information on the transition metal-silicon diatomic, ZrSi.     

Über die gegenseitige Einwirkung von flüssigen Filmen

Zusammenfassung Es wird gezeigt, da? ?ls?ure auf anges?uerter Permanganatl?sung einen Film ergibt, der au?erordentlich empfindlich gegenüber Einwirkungen anderer Flüssigkeiten ist. Die charakteristischen sternf?rmigen Teilchen dieses Filmes werden durch viele organische Flüssigkeiten und auch durch menschliche Blutseren ver?ndert. Besonders ausgepr?gt ist dies der Fall, wenn die Seren Wassermannreaktion zeigen, denn dann ist die Ver?nderung der Teilchen sehr einfacher Natur. Diese Reaktion kann aber nicht als wirklich spezifisch für syphilitische Seren betrachtet werden, da die Seren gewisser Patienten, die jedoch nicht syphilitisch sind, ganz ?hnliche Reaktionen ergeben. übersetzt von Rud. Walter (Leipzig). Die Verfasser danken den Herren Dr. Robb M. D. und Dr. Ross M. B. C. M. für ihre wertvolle Unterstützung bei diesen Untersuchungen.     

Binary inorganic salt mixtures as high conductivity liquid electrolytes for >100 degrees C fuel cells

We report the successful application of low-melting inorganic salts with protonated cations (e.g. ammonium) as electrolytes in fuel cells operating in the temperature range 100-200 degrees C, where even with unoptimized electrodes, cell performance is comparable to that of the phosphoric acid fuel cell operating with optimized electrodes in the same temperature range, while open circuit voltages, and efficiencies at low current densities, can be much better--and there is no need for humidification or pressure to sustain performance.     

ADAPTIVE MANAGEMENT OF HARVEST RATES IN THE PRESENCE OF A RISK AVERSE UTILITY FUNCTION

Previous research on adaptive harvest strategies has suggested that it should rarely be optimal to introduce deliberate, probing variations in harvest rates in order to reduce uncertainty about production parameters, when there is strong aversion to the risk of low catches. Here we show that this suggestion is incorrect for cases where the stock dynamics can be approximated by a simple power model and the objective is to maximize the sum over time of discounted logarithms of catches. In such cases, the objective function has a simple form that permits easy comparison between passively adaptive (certainty equivalent or cautious) versus actively adaptive policies involving probing variation in harvest rates. Probing is favored when there is high uncertainty about the power parameter that represents density dependence in the stock dynamics.