Electrostatic trapping of ammonia molecules

The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems.     

Substrate specificity of γ-secretase and other intramembrane proteases

γ-Secretase is a promiscuous protease that cleaves bitopic membrane proteins within the lipid bilayer. Elucidating both the mechanistic basis of γ-secretase proteolysis and the precise factors regulating substrate identification is important because modulation of this biochemical degradative process can have important consequences in a physiological and pathophysiological context. Here, we briefly review such information for all major classes of intramembranously cleaving proteases (I-CLiPs), with an emphasis on γ-secretase, an I-CLiP closely linked to the etiology of Alzheimer’s disease. A large body of emerging data allows us to survey the substrates of γ-secretase to ascertain the conformational features that predispose a peptide to cleavage by this enigmatic protease. Because substrate specificity in vivo is closely linked to the relative subcellular compartmentalization of γ-secretase and its substrates, we also survey the voluminous body of literature concerning the traffic of γ-secretase and its most prominent substrate, the amyloid precursor protein. Received 4 October 2007; received after revision 1 December 2007; accepted 7 December 2007     

Changes in acid phosphatase activity in 6 tissues of the fifth instar milkweed bug,Oncopeltus fasciatus

Summary Acid phosphatase activity in the hemolymph and cuticle was higher during the early part of the fifth instar than at any other time. The enzyme activity in the fat body, testes, salivary glands, and midgut was statistically the same throughout the instar.Acknowledgment. This research was supported in part by NSF grant GB 26542-Al to D. F.