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The toxin 3-nitropropionic acid 5 is produced by certain plants and fungi. It is a specific inhibitor of mitochondrial respiratory complex II. Fatalities after eating moldy sugarcane have been linked to 3-NP toxicity (1, 2). Ruminants grazing in regions with 3-NP-producing plants acquire resistance because of reduction of the nitro group to an amine by ruminal bacteria (3).The effectiveness of 3-NP in vivo after injection or oral administration has made it useful in studies involving tissues or whole animals. Ingestion of 3-NP results in neurodegeneration with symptoms resembling those of Huntington disease (4), and conversely Huntington disease results in a loss of complex II activity (5); thus 3-NP has been used to produce an animal model for the study of Huntington disease (6, 7). Symptoms also include convulsions, and 3-NP is being looked at for inducing a model of epilepsy (8). Prior subacute 3-NP poisoning seems to provide resistance to ischemic damage to nervous tissue by a preconditioning effect (9) similar to that resulting from mild ischemia.The target of 3-NP is Complex II, which is both a member of the Krebs tricarboxylic acid cycle (oxidizing succinate to fumarate) and an entry point for electrons into the respiratory chain at the level of ubiquinol. It consists of a large flavoprotein subunit containing covalently bound FAD, an iron-sulfur protein (IP) with three different iron-sulfur clusters, and two small membrane anchor subunits (chains C and D) ligating a single low spin heme of type B. Human genetic defects in the IP subunits or chains C or D lead to development of paragangliomas (10, 11). A mutation in chain C leads to premature aging in nematodes, presumably through excessive production of free radicals (12). Bacterial homologs succinate:quinone oxidoreductase (SQR) and menaquinol: fumarate oxidoreductase (FRD) in Escherichia coli have been studied as genetically manipulable models for the mitochondrial protein. Recent reviews cover this family of enzymes (13-18). X-ray crystallographic structures are available for a number of members of the family. The available mitochondrial structures and representative bacterial examples are listed in Table 1.The toxin 3-NP, structurally similar to and isoelectronic with the substrate succinate, is believed to be a suicide inactivator of Complex II. Alston et al. (19) proposed, based on previous observations and on their own experience with another flavoprotein, that the normal reaction pathway involves a temporary adduct with the N-5 nitrogen of flavin, which in the case of 3-NP collapses to a stable adduct resulting in permanent inactivation. Irreversible covalent modification of the flavin was ruled out by later work (20) examining the spectral change induced and showing that unmodified flavin peptide could be isolated from the inactivated complex by mild proteolysis. It was proposed that 3-NP is oxidized to 3-nitroacrylate, an unstable molecule that then reacts with some residue in the active site. A cysteine that was believed to be in the active ...

A matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) based approach was developed for the rapid analyses of cellular glycerophospholipids. Through multiplexed solvent-enabled optimization of analyte-matrix interactions during the crystallization process, over a 30-fold increase in S/N was achieved using 9-aminoacridine as matrix. The linearity of response (r 2 =0.99) and dynamic range of this method (over 2 orders of magnitude) were excellent. Moreover, through multiplexing ionization conditions by generating suites of different analytematrix interactions in the absence or presence of different alkali metal cations in the matrix, discrete lipid classes were highly and selectively ionized under different conditions resulting in the de facto resolution of lipid classes without chromatography. The resultant decreases in spectral complexity facilitated tandem mass spectrometric analysis through high energy fragmentation of lithiated molecular ions that typically resulted in informative fragment ions. Anionic phospholipids were also detected as singly negatively charged species that could be fragmented using MALDI tandem mass spectrometry leading to structural assignments. Collectively, these results identify a rapid, sensitive and highly informative MALDI-TOF MS approach for analysis of cellular glycerophospholipids directly from extracts of mammalian tissues without the need for prior chromatographic separation.

Gold nanoparticles, especially positron-emitter- labeled gold nanostructures, have gained steadily increasing attention in biomedical applications. Of the radionuclides used for nanoparticle positron emission tomography imaging, radiometals such as (64) Cu have been widely employed. Currently, radiolabeling through macrocyclic chelators is the most commonly used strategy. However, the radiolabel stability may be a limiting factor for further translational research. We report the integration of (64) Cu into the structures of gold nanoparticles. With this approach, the specific radioactivity of the alloyed gold nanoparticles could be freely and precisely controlled by the addition of the precursor (64) CuCl2 to afford sensitive detection. The direct incorporation of (64) Cu into the lattice of the gold nanoparticle structure ensured the radiolabel stability for accurate localization in vivo. The superior pharmacokinetic and positron emission tomography imaging capabilities demonstrate high passive tumor targeting and contrast ratios in a mouse breast cancer model, as well as the great potential of this unique alloyed nanostructure for preclinical and translational imaging.

We describe a high-resolution, high-sensitivity negative-tone photoresist technique that relies on bottom-up preassembly of differential polymer components within cylindrical polymer brush architectures that are designed to align vertically on a substrate and allow for top-down single-molecule line-width imaging. By applying cylindrical diblock brush terpolymers (DBTs) with a high degree of control over the synthetic chemistry, we achieved large areas of vertical alignment of the polymers within thin films without the need for supramolecular assembly processes, as required for linear block copolymer lithography. The specially designed chemical compositions and tuned concentric and lengthwise dimensions of the DBTs enabled high-sensitivity electron-beam lithography of patterns with widths of only a few DBTs (sub-30 nm line-width resolution). The high sensitivity of the brush polymer resists further facilitated the generation of latent images without postexposure baking, providing a practical approach for controlling acid reaction/diffusion processes in photolithography.