Solution, interfacial, and membrane properties of gramicidin A.

On the basis of the calculated magnitude of the unidirectional flux through a gramicidin channel, it was predicted that a single conducting event should be sufficient to release trapped ²²Na⁺ or ⁴²K⁺ from phospholipid vesicles with a consequent apparent loss of $\text{K}{}^{\mathrm{+}}\text{Na}{}^{\mathrm{+}}$ ion selectivity. In support of this prediction, the introduction of gramicidin to the bathing solution of phospholipid vesicles containing trapped ²²Na⁺ or ⁴²K⁺ led to a release of vesicle contents which was consistent with the expectation that, for each gramicidin dimer present, the contents of approximately one vesicle are released. The predicted apparent loss of $\text{K}{}^{\mathrm{+}}\text{Na}{}^{\mathrm{+}}$ selectivity was also observed. Evidence was also presented suggesting some movement of gramicidin from vesicle to vesicle. The fluorescent intensity of gramicidin decreases with time when added to aqueous solutions at very low concentrations. It is proposed that this is a consequence of the extremely low solubility of gramicidin in water. On the basis of area per molecule calculations at the air-water interface, it was argued that the most likely conformation of gramicidin existing at the air-water interface, of those proposed in the literature, was that of Π_L,D⁶ helix.     

A new antibiotic with known resistance factors,G418, inhibits plant cells

Growth rates of two lines of tobacco ($\text{Nicotiana}\text{tabacum}$) cell suspension cultures were measured in the presence or absence of G418, a new 2-deoxystreptamine antibiotic related to Gentamycin. Cell growth rates of $\text{N}$. $\text{tabacum}$ cv. Burley were inhibited at drug concentrations as low as 1.65 × 10^?7 M. At 4 × 10^?7 M, the doubling time was increased from 1.5 days (control) to 2.3 days (treatment). The drug was lethal to cells at 4 × 10^?6 M, and inhibition was irreversible. Cells of $\text{N}$. $\text{tabacum}$ cv. Wisconsin 38 also were inhibited by the drug, although at slightly higher concentrations (ca. 2–5 fold).In view of our findings, G418 and its associated resistance factors could be of great value in plant genetic engineering.     

The Akt kinase signals directly to endothelial nitric oxide synthase.

Endothelial nitric oxide synthase (eNOS) is an important modulator of angiogenesis and vascular tone [1]. It is stimulated by treatment of endothelial cells in a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent fashion by insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF) [2] [3] and is activated by phosphorylation at Ser1177 in the sequence RIRTQS(1177)F (in the single-letter amino acid code) [4]. The protein kinase Akt is an important downstream target of PI 3-kinase [5] [6], regulating VEGF-stimulated endothelial cell survival [7]. Akt phosphorylates substrates within a defined motif [8], which is present in the sequence surrounding Ser1177 in eNOS. Both Akt [5] [6] and eNOS [9] are localized to, and activated at, the plasma membrane. We found that purified Akt phosphorylated cardiac eNOS at Ser1177, resulting in activation of eNOS. Phosphorylation at this site was stimulated by treatment of bovine aortic endothelial cells (BAECs) with VEGF or IGF-1, and Akt was activated in parallel. Preincubation with wortmannin, an inhibitor of Akt signalling, reduced VEGF- or IGF-1-induced Akt activity and eNOS phosphorylation. Akt was detected in immunoprecipitates of eNOS from BAECs, and eNOS in immunoprecipitates of Akt, indicating that the two enzymes associate in vivo. It is thus apparent that Akt directly activates eNOS in endothelial cells. These results strongly suggest that Akt has an important role in the regulation of normal angiogenesis and raise the possibility that the enhanced activity of this kinase that occurs in carcinomas may contribute to tumor vascularization and survival.     

Assessment of Human Sleep Depth Is Being De-Standardized by Recently Advised EEG Electrode Locations

Human sleep depth was traditionally assessed by scoring electro-encephalographic slow-wave amplitudes at the globally standardized C4-M1 electrode derivation. Since 2007, the American Association of Sleep Medicine (AASM) has accepted three additional derivations for the same purpose. These might well differ in slow wave amplitudes which would bias the scorings. Some derivations might also introduce large inter-individual variability. We compared mean and variability of slow wave amplitudes between six derivations including the four AASM ones. Slow wave amplitudes in those derivations were simultaneously measured using automated analysis in 29 patients. Each amplitude was divided by the average from the six derivations, thus removing shared factors such as age, gender and sleep depth while retaining factors that differ between the derivations such as caused by local skull characteristics, electrode distance and neuronal dipole orientation. The remaining inter-individual variability differed significantly and up to a factor of two between the AASM derivations. The amplitudes differed significantly and up to 60% between the AASM derivations, causing substantial scoring bias between centres using different derivations. The resulting de-standardization most likely affects any patient group because the amplitude differences were consistent over diagnoses, genders, and age. Derivation-dependent amplitude thresholds were proposed to reduce the scoring bias. However, it would be better to settle on just one derivation, for instance Cz-Oz or Fpz-Cz because these have lowest variability while matching the traditional C4-M1 amplitudes.     

LIFE-HISTORY TRAITS: ADAPTATIONS OR EFFECTS?

Summary

Kemp, A. C. 1985. Life-history traits: adaptations or effects? Ostrich 56:147-150.

Attention is drawn to the epigeneticist viewpoint concerning life-history traits, whereby differences between organisms are considered as effects of, among other things, scaling relationships. The recent papers of Western &; Ssemakula (1982) and Calder (1983) have shown the extent to which variation in life-history traits of endotherms can be explained by scaling, mainly to body size, brain size and body temperature. Collection of comparative data and the search for scaling relationships in birds is encouraged.     

Control of feather keratin synthesis by the availability of keratin mRNA

The relative timing of the synthesis of keratin and its mRNA in the developing chick embryo feather has been examined. Study of both active mRNA in polysomes, and of the total number of mRNA sequences in the tissue, leads to the conclusion that the rate-limiting step in the synthesis of keratin is the accumulation in the cytoplasm of its mRNA.     

Spatial requirements for location of basic residues in peptide substrates for smooth muscle myosin light chain kinase

The requirement of basic residues as substrate specificity determinants for the chicken gizzard myosin light chain kinase has been studied using synthetic peptide analogs of the local phosphorylation site sequence in the myosin light chains, Lys-Lys-Arg13-Pro-Gln-Arg16-Ala-Thr-Ser19-Asn-Val-Phe- Ala. The basic residue, Arg-16, was found to have a strong influence on the kinetics of phosphorylation similar to that reported previously for the three adjacent residues, Lys-11, Lys-12, and Lys-13 (Kemp, B. E., Pearson, R. B., and House, C. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 7471-7475). The location of Arg-16 in relation to Ser-19 as well as the distance between Arg-13 and Arg-16 had a profound effect on both the kinetics and the site specificity of phosphorylation. Placement of Arg-16 at position 15 resulted in a complete switch in phosphorylation site specificity from Ser-19 to Thr-18. Increasing the number of alanine residues between Arg-13 and Arg-16 in the model peptide, Lys-Lys-Arg-(Ala)n-Arg-Ala-Thr-Ser-Asn-Val-Phe-Ala, also influenced the kinetics and site specificity of peptide phosphorylation. With two or three alanines (n = 2 or 3), the apparent Km was 7.5 and 10 microM, respectively, and 97% of the phosphate was esterified to Ser-19. Increasing or decreasing the number of alanines (n = O to n = 4) was accompanied by an increase in the apparent Km and phosphorylation of both Thr-18 and Ser-19. These results support the concept that both the presence and location of basic residues play an essential role in the substrate specificity of the smooth muscle myosin light chain kinase.