Spatial patterns in coupled biochemical oscillators

Summary The effects of diffusion on the dynamics of biochemical oscillators are investigated for general kinetic mechanisms and for a simplified model of glycolysis. When diffusion is sufficiently rapid a population of oscillators relaxes to a globally-synchronized oscillation, but when diffusion of one or more species is slow enough, the synchronized oscillation can be unstable and a nonuniform steady state or an asynchronous oscillation can arise. The significance of these results vis-a-vis models of contact inhibition and zonation patterns is discussed.     

Virions of primary human immunodeficiency virus type 1 isolates resistant to soluble CD4 (sCD4) neutralization differ in sCD4 binding and glycoprotein gp120 retention from sCD4-sensitive isolates.

Primary isolates of human immunodeficiency virus type 1 (HIV-1) are much less sensitive to neutralization by soluble CD4 (sCD4) and sCD4-immunoglobulin (Ig) chimeras (CD4-IgG) than are HIV-1 strains adapted to growth in cell culture. We demonstrated that there are significant reductions (10- to 30-fold) in the binding of sCD4 and CD4-IgG to intact virions of five primary isolates compared with sCD4-sensitive, cell culture-adapted isolates RF and IIIB. However, soluble envelope glycoproteins (gp120) derived from the primary isolate virions, directly by detergent solubilization or indirectly by recombinant DNA technology, differed in affinity from RF and IIIB gp120 by only one- to threefold. The reduced binding of sCD4 to these primary isolate virions must therefore be a consequence of the tertiary or quaternary structure of the envelope glycoproteins in their native, oligomeric form on the viral surface. In addition, the rate and extent of sCD4-induced gp120 shedding from these primary isolates was lower than that from RF. We suggest that reduced sCD4 binding and increased gp120 retention together account for the relative resistance of these primary isolates to neutralization by sCD4 and CD4-IgG and that virions of different HIV-1 isolates vary both in the mechanism of sCD4 binding and in subsequent conformational changes in their envelope glycoproteins.     

A strain difference in the daily rhythm of glyceraldehyde-3-phosphate dehydrogenase activity in the mouse

Journal of Comparative Physiology A - A/J mice differ from C57BL/6J mice in the time of the daily peak of activity of glyceraldehyde-3-phosphate dehydrogenase (GAPD) in thymus and in thyroid....     

The structural and functional interrelationships of muscarinic acetylcholine receptor subtypes

Molecular cloning of the genes encoding the muscarinic acetylcholine receptors has shown that receptor subtypes classified on the basis of pharmacological properties are related polypeptides encoded by distinct genes. These studies have also revealed the existence of novel muscarinic receptor subtypes. Functional analysis of each of the subtypes expressed in mammalian cells indicates that the different subtypes activate distinct biochemical pathways, a finding that explains the tissue-specific physiological response elicited by the neurotransmitter, acetylcholine.     

Functionally distinct G proteins selectively couple different receptors to PI hydrolysis in the same cell

The number of G proteins identified by molecular cloning exceeds the number of known G protein functions. Here we show that a cell can possess multiple G proteins that carry out a similar function, the activation of phospholipase C, but couple selectively to different receptors, which are endogenous to the cell or introduced by DNA transfection. These G proteins (termed Gp) can be distinguished by their sensitivity to pertussis toxin. The assignment of a given Gp pathway to specific receptors is confirmed by the additivity relationships of the PI hydrolysis response mediated by the different receptors. Significantly different amounts of PI hydrolysis are activated through each Gp pathway, suggesting that Gp proteins also differ in their coupling to phospholipase C. These results indicate that distinct Gp pathways in a given cell exist to couple different receptors to PI hydrolysis selectively, and may specify the nature of the cellular response to different receptors by determining the magnitude of PI hydrolysis.     

Activity rhythms of enzymes in human red blood cell suspensions

Abstract

We have established the presence of a rhythm in the activity of 4 enzymes in in‐vitro cell suspensions of human red blood cells. Glucose 6‐phosphate dehydrogenase and glutamate oxaloacetate transaminase demonstrated semicircadian patterns of activity, while acid phosphatese and acetylcholine esterase exhibited circadian activity rhythms. The ratios between the highest to lowest activities varied from 2:1 to 10:1 among the various enzymes. The affinity of glucose 6 phosphate dehydrogenase to its substrate and coenzyme remained constant throughout the cycle. No evidence was obtained for the presence of a soluble inhibitor at the lower levels of the activity. Sonication of hemolysates with low glucose 6 phosphate dehydrogense activity yielded additional activity comparable to that of the peak activity. Sonication of hemolysates from the time of the peak activity did not change the original activity. The observations point to a role of the cell membrane in the biological clock.     

Tools and methodologies to support more sustainable biofuel feedstock production

Increasingly, government regulations, voluntary standards, and company guidelines require that biofuel production complies with sustainability criteria. For some stakeholders, however, compliance with these criteria may seem complex, costly, or unfeasible. What exiting tools, then, might facilitate compliance with a variety of biofuel-related sustainability criteria? This paper presents four existing tools and methodologies that can help stakeholders assess (and mitigate) potential risks associated with feedstock production, and can thus facilitate compliance with requirements under different requirement systems. These include the Integrated Biodiversity Assessment Tool (IBAT), the ARtificial Intelligence for Ecosystem Services (ARIES) tool, the Responsible Cultivation Areas (RCA) methodology, and the related Biofuels + Forest Carbon (Biofuel + FC) methodology.     

Apoptosis control by death and decoy receptors

The death receptors Fas and tumor necrosis factor receptor 1 (TNFR1) trigger apoptosis upon engagement by their cognate death ligands. Recently, researchers have discovered several novel homologues of Fas and TNFR1: DR 3, 4, 5, and 6 function as death receptors that signal apoptosis, whereas DcR 1, 2, and 3 act as decoys that compete with specific death receptors for ligand binding. Further, mouse gene knockout studies have enabled researchers to delineate some of the signaling pathways that connect death receptors to the cell's apoptotic machinery.     

UNCovering the molecular machinery of dependence receptor signaling

Dependence receptors send opposite signals in the presence or absence of ligand, but the underlying mechanisms have been elusive. In this issue of Molecular Cell, Guenebeaud et al. (2010) elucidate the molecular signaling machinery of the dependence receptor UNC5B.