Amyloid-β (Aβ) peptide aggregation is known to play a central role in the etiology of Alzheimer’s disease (AD). Among various aggregates, low-molecular weight soluble oligomers of Aβ are increasingly believed to be the primary neurotoxic agents responsible for memory impairment. Anionic interfaces are known to influence the Aβ aggregation process significantly. Here, we report the effects of interfaces formed by medium-chain (C9–C12), saturated non-esterified fatty acids (NEFAs) on Aβ42 aggregation. NEFAs uniquely affected Aβ42 aggregation rates that depended on both the ratio of Aβ:NEFA as well the critical micelle concentration (CMC) of the NEFAs. More importantly, irrespective of the kind of NEFA used, we observed that two distinct oligomers, 12–18 mers and 4–5 mers were formed via different pathway of aggregation under specific experimental conditions: (i) 12–18 mers were generated near the CMC in which NEFAs augment the rate of Aβ42 aggregation towards fibril formation, and, (ii) 4–5 mers were formed above the CMC, where NEFAs inhibit fibril formation. The data indicated that both 12–18 mers and 4–5 mers are formed along an alternate pathway called ‘off-pathway’ that did not result in fibril formation and yet have subtle structural and morphological differences that distinguish their bulk molecular behavior. These observations, (i) reflect the possible mechanism of Aβ aggregation in physiological lipid-rich environments, and (ii) reiterate the fact that all oligomeric forms of Aβ need not be obligatory intermediates of the fibril formation pathway.

Methylammonium uptake was studied in a glutamine auxotroph of the cyanobacterium Anabaena cycadeae lacking glutamine synthetase activity. The uptake pattern was found to be biphasic, consisting of an initial fast phase lasting up to 60 s followed by a slower second phase. When cells were preincubated with L-methionine-DL-sulphoximine, an irreversible inhibitor of glutamine synthetase activity, the second uptake phase was abolished although the first phase was unaffected. Since the glutamine auxotroph did not have any glutamine synthetase activity the inhibition of the second phase by L-methionine-DL-sulphoximine could not have been due to the inhibition of glutamine synthetase activity. Thus, it is suggested that the two uptake phases may represent two different ammonium transport systems, the second one being sensitive to L-methionine-DL-sulphoximine.Ammonium transport Anabaenacycadeae C.yanobacteria

SUMOylation is a reversible post translational modification of proteins that regulates protein stabilization, nucleocytoplasmic transport, and protein-protein interactions. Several viruses and bacteria modulate host SUMOylation machinery for efficient infection. Plasmodium sporozoites are infective forms of malaria parasite that invade mammalian hepatocytes and transforms into exoerythrocytic forms (EEFs). Here, we show that during EEF development, the distribution of SUMOylated proteins in host cell nuclei was significantly reduced and expression of the SUMOylation enzymes was downregulated. Plasmodium EEFs destabilized the host cytoplasmic protein SMAD4 by inhibiting its SUMOylation. SUMO1 overexpression was detrimental to EEF growth, and insufficiency of the only conjugating enzyme Ubc9/E2 promoted EEF growth. The expression of genes involved in suppression of host cell defense pathways during infection was reversed during SUMO1 overexpression, as revealed by transcriptomic analysis. The inhibition of host cell SUMOylation was also observed during Toxoplasma infection. We provide a hitherto unknown mechanism of regulating host gene expression by Apicomplexan parasites through altering host SUMOylation.

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SUMMARYA novel class of azide-resistant mutants of N. muscorum is described in which azide caused inhibition of heterocyst differentiation and nitrogen fixation without causing inhibition of growth. The results indicate the utilization of azide, as a fixed nitrogen source, by the mutant strain. An increase in the ability to take up azide and in the phycocyanin/chlorophyll ratio following growth of the mutant in azide-containing medium are additional findings which support the conclusion that the mutant utilizes azide as a source of nitrogen. In the parental strain, Ca^^-dependent and Mg^+-dependent ATPases, and cellular nitrate reductase were inhibited by azide. The corresponding ATPases from the mutant strain were not inhibited by azide. There was evidence, in cell-free extracts, for an enzyme system which utilized azide as an electron acceptor and NADPH-ferredoxin as electron donor. The activity of this system was significantly higher (on a protein basis) in cells of the mutant grown on azide than in cells of either the parent or the mutant when grown on nitrate.It is suggested that the azide resistance of this class of mutant is due to a mutation which leads to azide resistant Ca2+-and Mg^^-ATPases. Such a mutation may allow an azide utilizing system, inherently present in both parent and mutant strains, to be expressed.