Redescription of Alinema amazonicum (Travassos, 1960) n. comb., a philometrid nematode with unusual morphology

Nematodes (1 male and numerous females) of the Philometridae were collected from the mesentery of 2 species of pimelodid catfishes, Calophysus macropterus and Perrunichthys perruno, from the Amazon River basin (fishmarket in Iquitos, Loreto District) in Peru. A detailed study of their morphology (including scanning electron microscopy) and a reexamination of the type and voucher specimens of Philometra amazonica Travassos, 1960, from Brazilian catfishes confirmed that they belong to this species and that Philometra (Alinema) alii Rasheed, 1963 is its junior synonym. Because of some marked morphological peculiarities of this species (presence of minute peribuccal sclerotized formations, a functional vagina and vulva in gravid female, and structure of the male tail), the validity of an independent genus, Alinema Rasheed, 1963, is confirmed, to which this species is transferred as Alinema amazonicum (Travassos, 1960) n. comb. This is the first record of this parasite from Peru, and P. perruno represents its new host record.     

Effect of alcohols on aqueous lysozyme-lysozyme interactions from static light-scattering measurements

Alcohols have been widely used as protein denaturants, precipitants and crystallization reagents. We have studied the effect of alcohols on aqueous hen-egg lysozyme self-interactions by measuring the osmotic second virial coefficient (B22) using static light scattering. Addition of alcohols increases B22, indicating stronger protein-protein repulsion or weaker attraction. For the monohydric alcohols used in this study (methanol, ethanol, 1-propanol, n-butanol, iso-butanol and trifluoroethanol), B22 for lysozyme reaches a common plateau at approximately 5% (v/v) alcohol, while glycerol increases B22 more than monohydric alcohols. For a 0.05 M NaCl hen-egg lysozyme solution at pH 7, B22 increases from 2.4 x 10(-4) to 4.7 x 10(-4) ml mol/g2 upon addition of monohydric alcohols and to 5.8 x 10(-4) ml mol/g2 upon addition of glycerol. We describe the alcohol effect using a simple model that supplements the DLVO theory with an additional alcohol-dependent term representing orientation-averaged hydrophobic interactions. In this model, the increased lysozyme repulsive forces in the presence of monohydric alcohols are interpreted in terms of adsorption of alcohol molecules on hydrophobic sites on the protein surface. This adsorption reduces attractive hydrophobic protein-protein interactions. A thicker lysozyme hydration layer in aqueous glycerol solution can explain the glycerol-increased lysozyme-lysozyme repulsion.     

<Superscript>13</Superscript>C-detected NMR experiments for measuring chemical shifts and coupling constants in nucleic acid bases

The paper presents a set of two-dimensional experiments that utilize direct ¹³C detection to provide proton–carbon, carbon–carbon and carbon–nitrogen correlations in the bases of nucleic acids. The set includes a ¹³C-detected proton–carbon correlation experiment for the measurement of ¹³C–¹³C couplings, the CaCb experiment for correlating two quaternary carbons, the HCaCb experiment for the ¹³C–¹³C correlations in cases where one of the carbons has a proton attached, the HCC-TOCSY experiment for correlating a proton with a network of coupled carbons, and a ¹³C-detected ¹³C–¹⁵N correlation experiment for detecting the nitrogen nuclei that cannot be detected via protons. The IPAP procedure is used for extracting the carbon–carbon couplings and/or carbon decoupling in the direct dimension, while the S³E procedure is preferred in the indirect dimension of the carbon–nitrogen experiment to obtain the value of the coupling constant. The experiments supply accurate values of ¹³C and ¹⁵N chemical shifts and carbon–carbon and carbon–nitrogen coupling constants. These values can help to reveal structural features of nucleic acids either directly or via induced changes when the sample is dissolved in oriented media. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Light activation of an innate olfactory avoidance response in Drosophila

How specific sensory stimuli evoke specific behaviors is a fundamental problem in neurobiology. In Drosophila, most odorants elicit attraction or avoidance depending on their concentration, as well as their identity [1]. Such odorants, moreover, typically activate combinations of glomeruli in the antennal lobe of the brain [2-4], complicating the dissection of the circuits translating odor recognition into behavior. Carbon dioxide (CO2), in contrast, elicits avoidance over a wide range of concentrations [5, 6] and activates only a single glomerulus, V [5]. The V glomerulus receives projections from olfactory receptor neurons (ORNs) that coexpress two GPCRs, Gr21a and Gr63a, that together comprise a CO2 receptor [7-9]. These CO2-sensitive ORNs, located in the ab1 sensilla of the antenna, are called ab1c neurons [10]. Genetic silencing of ab1c neurons indicates that they are necessary for CO2-avoidance behavior [5]. Whether activation of these neurons alone is sufficient to elicit this behavior, or whether CO2 avoidance requires additional inputs (e.g., from the respiratory system), remains unclear. Here, we show that artificial stimulation of ab1c neurons with light (normally attractive to flies) elicits the avoidance behavior typical of CO2. Thus, avoidance behavior appears hardwired into the olfactory circuitry that detects CO2 in Drosophila.