Effect of adrenocorticotrophic hormone on the activity of sterol ester hydrolase from rat brain

Adrenocorticotrophic hormone (ACTH) stimulates in vitro the hydrolysis of oleoylcholesterol by a sterol ester hydrolase from rat brain synaptosomes. The stimulatory effect involves an alkaline shift of the pH optimum of catalysis and culminates at pH 6 with a 15 to 20-fold increase in lipolytic rates. The effect requires trace amount of organic solvent in the substrate emulsion and is dependent on the NH₂-terminal sequence extending through the basic amino acid residues at positions 15–18. The hormonal stimulation is decreased when a lipid-depleted preparation is used as enzyme source, and fully restored upon addition of lecithin. The results raise the possibility that ACTH may have a neuro-hormonal role in brain via modulation of local lipolytic processes.     

Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones

A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer.     

Nitrogen Addition Could Shift Plant Community Composition in a Restored California Salt Marsh

At a salt marsh restoration site, fertilizer trials to improve height growth of Spartina foliosa (a C₄ perennial grass that can reach 140 cm) appeared to favor Salicornia bigelovii (an annual C₃ succulent under 40 cm tall) where the two species co-occurred on the marsh plain. This observation prompted a field experiment to examine the potential for nitrogen (N) addition to shift community composition. Without N addition, total stem length and stem density of S. foliosa did not respond to the presence or absence of S. bigelovii. But where N was added, S. foliosa growth increased only where S. bigelovii was removed from plots. S. bigelovii responded strongly to fertilizer, with mean heights matching those of S. foliosa and 600% increases in biomass, branching, and seed production (to more than 1 million seeds/m²). Soil N also increased seasonally where S. bigelovii was present, suggesting that this species may aid accumulation of N at restoration sites with poor soils. S. foliosa growth is greatest at lower elevations along tidal creeks where it occurs alone. Beyond creek edges, where S. bigelovii and other potential competitors occur, S. foliosa is unlikely to grow tall even with N addition. Thus, there is little point in trying to force mixed-species stands to provide tall S. foliosa for nesting by an endangered bird, Rallus longirostris levipes (the Light-footed Clapper Rail). A marsh construction design that maximizes tidal creek edges is thus recommended when restoration goals include providing habitat for clapper rails.     

Synthesis and structure–activity studies of novel homomorpholine oxazolidinone antibacterial agents

A novel series of oxazolidinones were synthesized in which the morpholine C-ring of linezolid was replaced with homomorpholine. In addition to investigating the effect of a homomorpholine C-ring on antibacterial activity, the effect of des-, mono-, di-, and tri-fluoro substitution on the phenyl B-ring was investigated as well. Various C-5 functional groups were also examined, including acetamides and triazoles and carboxamides.