NMR studies of the conformational change in human N-p21ras produced by replacement of bound GDP with the GTP analog GTP gamma S.

1H-Detected 15N-edited NMR in solution was used to study the conformational differences between the GDP- and GTP gamma S-bound forms of human N-p21ras. The amide protons of 15N-labeled glycine and isoleucine were observed. Resonances were assigned to residues of particular interest, glycines-60 and -75 and isoleucines-21 and -36, by incorporating various 13C-labeled amino acids in addition to [15N]glycine and [15N]iosleucine and by replacing Mg2+ by Co2+. When GTP gamma S replaced GDP in the active site of p21ras, only 5 of the 14 glycine amide resonances show major shifts, indicating that the conformational effects are fairly localized. Responsive glycines-10, -12, -13, and -15 are in the active site. Gly-75, located at the far end of a conformationally-active loop and helix, also responds to substitution of GTP gamma S for GDP, while Gly-77 does not, supporting a role for Gly-75 as a swivel point for the conformational change. The amide proton resonances of isoleucines-36 and -21 and a third unidentified isoleucine also undergo major shifts upon replacement of GDP by GTP gamma S. Thus, the effector-binding loop containing Ile-36 is confirmed to be involved in the conformational change, and the alpha-helix containing Ile-21 is also shown to be affected.     

Immediate and delayed effects of poor developmental conditions on growth and flight ability of juvenile mourning doves Zenaida macroura

Adaptations that minimize the effects of stress are important components of avian development and have a role in structuring the relationship between development and fitness. I examined the effect of experimental manipulations of developmental stress during the nestling and fledgling stages on weight gain, growth in structural size, and take‐off flight speed of juvenile mourning doves Zenaida macroura. Brood size was manipulated during the nestling stage (≤11 days) and feeding rates during the fledgling stage (13–25 days) using a full factorial design. Effects of nutritional stress differed between the two treatments and depended on the response that was measured and the age at which it was measured. Treatment effects on flight ability were delayed and were greater for the treatment during the nestling stage than during the fledgling stage. Immediate treatment effects were greater than delayed effects on weight and size. Young were able to minimize effects of stress on flight ability at early ages when they would be most vulnerable to predation. However, by 90 days birds from enlarged broods were slower and flight time at 90 days was negatively correlated with weight and size at 25 days. There was no evidence for a cost of compensatory growth after experimental treatments ended on flight ability at 90 days. Results suggest that the effects of stress occur in a hierarchical manner across phenotypic components and that at early ages flight ability is prioritized through phenotypic plasticity.     

A programmable environmental system for maintenance and observation of individually housed ticks

This paper describes an inexpensive, space-saving, and labor-efficient method for housing and making repeated observations of individual ticks held under specific photoperiodic, temperature, and humidity conditions. Using 96-well assay plates to house ticks, various developmental parameters, sex, survival, etc., of several thousand individual ticks can be recorded routinely in less than 1 hr. This design also permits more than 3,500 individual ticks to be maintained in 1 small (18.9-L) aquarium that serves as a humidity chamber. A small, unilluminated constant temperature incubator was converted inexpensively into a light and temperature programmable unit to contain the aquarium by adding a timing system, light fixture, and a second thermostat.     

Cytochrome P450cam-catalyzed oxidation of a hypersensitive radical probe.

trans-1-Phenyl-2-vinylcyclopropane, a hypersensitive radical probe, is oxidized by cytochrome P450cam (CYP101) to a diastereomeric mixture of the corresponding epoxide (81%), (trans-2-phenylcyclopropyl)acetaldehyde (6%), and trans-5-phenyl-2-penten-1,5-diol (13%). trans-5-Phenyl-2-penten-1-ol and (trans-2-phenylcyclopropyl)ethane-1,2-diol are not detectably formed. Authentic standards of all the products have been synthesized and used to establish the identities (or the absence) of the metabolites. Studies with [18O]H2O demonstrate that the oxygens at positions 1 and 5 in the rearranged diol derive from molecular oxygen and water, respectively. Catalytic turnover of the enzyme is required for product formation from the olefin, but incubation of the epoxide metabolite with the enzyme, or with buffer alone, yields both the aldehyde and the rearranged diol products. The absence of trans-5-phenyl-2-penten-1-ol implies that the lifetime of the putative radical intermediate is so short that its existence as a discrete entity is questionable. A cationic intermediate is unlikely but cannot be excluded because the same metabolites are formed in a secondary reaction, even at pH 8.0, from the epoxide. The results provide no evidence for the involvement of radicals or cations in the epoxidation reaction, in agreement with results on the oxidation of olefins in organic solvents by metalloporphyrin catalysts.     

Competition between native and monoacetylated polymyxin for charged adsorption sites

The native antibiotic polymyxin B, carrying five positive charges, displaces the monoacetylated on from its adsorbed state at the interface between negatively charged lipid layers ans water. A simulation model for asdorption, governed by electrostatic forces, is presented. The model adequently representes the competitive adsorption kinetics and equilibria.     

Deoxyribonucleic Acid Base Composition of Lactobacilli Determined by Thermal Denaturation

Moles per cent guanine plus cytosine content of 16 lactobacilli provided three taxonomic groups: I, 32.4 to 38.3% with five species; II, 42.7 to 48.0% with six species; III, 49.0 to 51.9% with five species.