The ovicidal activity of cis-dehydromatricaria ester: time-dependance of its enhancement by UV light

Freshly laid eggs of Drosophila melanogaster were treated with the polyacetylenic compound cis-dehydromatricaria ester. The toxicity of the chemical was enhanced by treatments with long-wavelength ultraviolet light, and the maximum effect was observed when the UV irradiation was performed 4-5 h after the initial contact of the eggs with the chemical.     

Geometric phase shifts in chemical oscillators

One of the most remarkable developments in quantum mechanics in recent years has been the discovery that when a system is moved adiabatically around a closed loop in parameter space there occurs, besides the familiar dynamical phase shift, an additional phase shift (sometimes referred to as 'Berry's phase') that is purely geometric in nature. The dynamical phase shift, which results from the variation of the period of the oscillatory system with the change in parameters, is relatively easily understood and is proportional to the time over which the parameter change occurs. The geometric phase shift, on the other hand, is less intuitive and depends on the curvature of the surface in parameter space bounded by the closed path, but is independent of the time taken to traverse the circuit. Here we present evidence for time-independent geometric phase shifts in numerical solutions for a model of an oscillating chemical reaction. The conditions for the occurrence of such shifts seem to be sufficiently general that geometric phase effects should be experimentally observable in essentially all chemical oscillators as well as in biological networks such as the brain and the central nervous system, where phase control is of vital importance.     

Candida utilis as a convenient and safe substitute for the pathogenic yeastC. albicans in Daniels' phototoxicity test

Summary Candida utilis is a safe and convenient substitute for the pathogenic yeastC. albicans in phototoxicity tests. With both organisms 8-methoxypsoralen and -terthienyl give positive results while photodynamic compounds give negative results.Acknowledgments. We are grateful to the National Institutes of Health (GM24144) for financial assistance, and to Ms Nancy Budorick, Prof. A. Ferro, and Mr Carl Moshovitis for technical assistance and advice.     

Lysyl oxidase: an oxidative enzyme and effector of cell function

Lysyl oxidase (LOX) oxidizes the side chain of peptidyl lysine converting specific lysine residues to residues of alpha-aminoadipic-delta-semialdehyde. This posttranslational chemical change permits the covalent crosslinking of the component chains of collagen and those of elastin, thus stabilizing the fibrous deposits of these proteins in the extracellular matrix. Four LOX-like (LOXL) proteins with varying degrees of similarity to LOX have been described, constituting a family of related proteins. LOX is synthesized as a preproprotein which emerges from the cell as proLOX and then is processed to the active enzyme by proteolysis. In addition to elastin and collagen, LOX can oxidize lysine within a variety of cationic proteins, suggesting that its functions extend beyond its role in the stabilization of the extracellular matrix. Indeed, recent findings reveal that LOX and LOXL proteins markedly influence cell behavior including chemotactic responses, proliferation, and shifts between the normal and malignant phenotypes.     

The ovicidal activity ofcis-dehydromatricaria ester: time-dependance of its enhancement by UV light

Summary Freshly laid eggs ofDrosophila melanogaster were treated with the polyacetylenic compoundcis-dehydromatricaria ester. The toxicity of the chemical was enhanced by treatments with long-wavelength ultraviolet light, and the maximum effect was observed when the UV irradiation was performed 4–5 h after the initial contact of the eggs with the chemical.We are grateful to Professor E. Spiess for advice and assistance, and to the National Institutes of Health (GM 24144) for financial support.     

Mode of action of yeast killer toxins: channel formation in lipid bilayer membranes

The toxic action of yeast killer proteins seems to involve selective functional damage to the plasma membrane of the sensitive cell. Physiological effects include leakage of K+ (refs 1, 2), inhibition of active transport of amino acids and acidification of the cell interior. These effects are strikingly similar to the effects of certain bacterial colicins which have been demonstrated previously to form channels in membranes. Proposed mechanisms of action have usually postulated a limited permeability change induced by the toxin in the plasma membrane. We report here that a killer toxin from the yeast Pichia kluyveri forms ion-permeable channels in phospholipid bilayer membranes, and we propose that the in vitro electrophysiological properties of these channels account for the morbid effects observed in intoxicated cells. A preliminary account of this work has appeared elsewhere.     

集合体与复杂系统的设计

人们需要计算机的功能不断增加，而希望计算机的价格不断降低，体积不断缩小，这些需求促使建立在自适应分布式计算机基础上的一种新的计算范例形成。这种计算范例用于复杂工程系统的控制及优化，或者是自然系统的分析。这些问题只能通过一个大型的计算机共同体的联合行动才能解决，其中的每一个计算机都运行它们自己的复杂、分散的机器学习算法。当这样的系统与系统层次的性能规范相结合时就被称为集合体。本书奠定了集合体科学的基础，而且描述了为了优化性能应该怎样设计这类系统。