Electrophoretic analysis of clinical dextrans

Résumé On démontre que l'électrophorèse de dextrans cliniques peut être employée pour la détermination de leur poids moléculaire et de la polydispersité.     

A model for intracellular translocation of protein kinase C involving synergism between Ca2+ and phorbol esters

The activation of protein kinase C by diacylglycerol and by tumour promoters has implicated this enzyme in transmembrane signalling and in the regulation of the cell cycle. In vitro studies revealed that catalytic activity requires the presence of calcium and phospholipids with a preference for phosphatidylserine. Diacylglycerol and tumour promoters such as phorbol esters bind to the enzyme, leading to its activation while sharply increasing its affinity for Ca2+ and phospholipid. Addition of diacylglycerol analogues or phorbol esters to intact cells results in the phosphorylation of specific polypeptides. Several cellular processes, including hormone and neurotransmitter release and receptor down-regulation, are modulated by the activation of protein kinase C, while phorbol ester-induced stimulation of the enzyme in whole cells has been associated with its translocation from the cytoplasm to the plasma membrane. Moreover, the use of Ca2+ ionophores has revealed an apparent synergism between Ca2+ mobilization and protein kinase C activation. This synergism has recently also been found to apply to receptor down-regulation (ref. 23 and accompanying paper). Here we describe a reconstitution system in which intracellular translocation of protein kinase C and the synergism between Ca2+ and enzyme activators can be studied. The results suggest a rationale for concomitant Ca2+ mobilization and diacylglycerol formation in response to some hormones, neurotransmitters and growth factors.     

Herd immunity to helminth infection and implications for parasite control

Despite much research on immunological responses to helminth parasites, knowledge of the dynamic interplay between levels of herd immunity in humans and the rates of exposure, establishment and mortality of parasites remains limited. We describe here a simple mathematical model for the population dynamics of helminth infections which mirrors the development of a degree of acquired immunity within populations which are genetically heterogeneous with respect to immunological responsiveness. We interpret observed patterns in the age-specific intensity of infection and attempt to understand the possible effects of control measures based on chemotherapy and vaccination. Mass chemotherapy can, in some circumstances, reduce the level of herd immunity such that average worm burdens in the adult age classes rise above their precontrol levels. When certain individuals or groups are predisposed to heavy infection, selective or targeted drug treatment can have significantly greater impact than mass or random application. Conversely, model predictions suggest that effective parasite control by vaccination (if and when vaccines become available) is difficult to achieve in communities that are genetically heterogeneous in their ability to mount protective responses to infection.     

Trace metal requirements in total parenteral nutrition: A theoretical approach by mathematical modeling

Summary A new computer-based approach has been developed to assess the optimal doses of essential trace metal ions which should be included in nutritive mixtures, used in human total parenteral nutrition, to compensate for the ligand-induced losses of these metal ions. An example of application is given for zinc, copper and manganese.     

Molecular mechanisms of lipoprotein receptor signalling

The low-density lipoprotein (LDL) receptor is the prototype of a classical endocytosis receptor that mediates the uptake of extracellular ligands. Other members of the LDL receptor gene family, on the other hand, have been shown to regulate intracellular signalling cascades. Among these are the LDL receptor-related protein 1, LRP1, a promiscuous and ubiquitously expressed receptor which is critically involved in a multitude of diverse physiological processes; the Reelin receptors ApoER2 and VLDL receptor, which participate in neuronal development; and megalin, a multifunctional receptor expressed in various epithelia. In this review, we focus on recent developments that highlight similarities and differences between these related receptors and their biological function, and discuss open questions as to the underlying molecular mechanisms.     

The biosynthesis of diterpenoid alkaloids

Zusammenfassung Die diterpenoiden Alkaloide Browniin und Lycoctonin wurdenin vivo aus Mevalonsäure-2-¹⁴C hergestellt. Sie zeigten, aus Acetat-1-¹⁴C und -2-¹⁴C gewonnen, eine geringere Wirksamkeit. Die Biosynthese dieser Alkaloide scheint somit der der anderen Terpene analog.     

网络环境下的用户信息需求与高校图书馆信息服务

随着计算机技术、通信技术、网络技术的应用，图书馆服务模式发生了巨大变化。在分析传统信息服务模式的基础上，针对高校图书馆用户的信息需求，提出了网络环境下信息服务的新思路。