Actin-, myosin- and ubiquitin-dependent endocytosis

Endocytosis is a general term that is used to describe the internalization of external and plasma membrane molecules into the cell interior. In fact, several different mechanisms exist for the internalization step of this process. In this review we emphasize the work on the actin-dependent pathways, in particular in the yeastSaccharomyces cerevisiae, because several components of the molecular machinery are identified. In this yeast, the analysis of endocytosis in various mutants reveals a requirement for actin, calmodulin, a type I myosin, as well as a number of other proteins that affect actin dynamics. Some of these proteins have homology to proteins in animal cells that are believed to be involved in endocytosis. In addition, the demonstration that ubiquitination of some cell surface molecules is required for their efficient internalization is described. We compare the actin, myosin and ubiquitin requirements for endocytosis with recent results found studying these processes usingDictyostelium discoideum and animal cells.     

Soybean photosynthesis: simultaneous14CO2 and O2 estimates

Summary A method of estimating the photosynthetic rate of soybean leaves using an oxygen electrode is presented. The procedure is rapid, requires small samples and compares favourably with estimates by other techniques. Light saturation occurs at 1200 E·m^–2·sec^–1. The apparent K_m for HCO ₃ ^– is 3.2 mM at pH 7.6.     

A synthesis of 2:2:3-trimethylcyclohexane-1-carboxylic acid

Résumé L'acide cétonique deSamuel etManasse obtenu par la transformation du quinone camphorique a été déjà réduit par l'auteur avec formation d'un acide saturé, C₁₀H₁₈O₂, dont la constitution est maintenant prouvé par sa synthèse. L'auteur a trouvé aussi que l'éther méthylique de l'acide 2-méthylcyclopentan-1-ol-1-carboxylique fournit par transformation pinacolique un mélange de 2:2:3-triméthyl- et 2:2:6-triméthylcyclohexanones.     

Infrared metaphysics: radiation and theory-choice. Part 2

We continue our discussion of the competing arguments in favour of the unified theory and the pluralistic theory of radiation advanced by three nineteenth-century pioneers: Herschel, Melloni, and Draper. Our narrative is structured by a consideration of the epistemic criteria relevant to theory-choice; the epistemic focus highlights many little-known aspects of this relatively well-known episode. We argue that the acceptance of light-heat unity (and of the unified theory of radiation more generally) in this period cannot be credibly justified on the basis of common evaluative criteria such as simplicity and standard notions of explanatory power. Whether the consensus was justified by some other criteria remains an open question.     

On and beyond O2 binding: Hemoglobin and myoglobin revisited

The past decade of our laboratory's investigations into some aspects of heme proteins at first glance may seem marginal to the primary biological function of these proteins in O₂ binding and transport. But in fact, understanding long-range electron transfer mechanisms and the participation of hemoglobin and myoglobin in the generation of oxidative stress may provide relevant new biochemical insights.     

Ferrochelatase at the millennium: structures, mechanisms and [2Fe-2S] clusters

Ferrochelatase (E.C. 4.99.1.1, protoheme ferrolyase) catalyzes the insertion of ferrous iron into protoporphyrin IX to form protoheme (heme). In the past 2 years, the crystal structures of ferrochelatases from the bacterium Bacillus subtilis and human have been determined. These structures along with years of biophysical and kinetic studies have led to a better understanding of the catalytic mechanism of ferrochelatase. At present, the complete DNA sequences of 45 ferrochelatases from procaryotes and eucaryotes are available. These sequences along with direct protein studies reveal that ferrochelatases, while related, vary significantly in amino acid sequence, molecular size, subunit composition, solubility, and the presence or absence of nitric-oxide-sensitive [2Fe-2S] cluster.     

ING1 and ING2: multifaceted tumor suppressor genes

Inhibitor of Growth 1 (ING1) was identified and characterized as a “candidate” tumor suppressor gene in 1996. Subsequently, four more genes, also characterized as “candidate” tumor suppressor genes, were identified by homology search: ING2, ING3, ING4, and ING5. The ING proteins are characterized by a high homology in their C-terminal domain, which contains a Nuclear Localization Sequence and a Plant HomeoDomain (PHD), which has a high affinity to Histone 3 tri-methylated on lysine 4 (H3K4Me3). The ING proteins have been involved in the control of cell growth, senescence, apoptosis, chromatin remodeling, and DNA repair. Within the ING family, ING1 and ING2 form a subgroup since they are evolutionarily and functionally close. In yeast, only one gene, Pho23, is related to ING1 and ING2 and possesses also a PHD. Recently, the ING1 and ING2 tumor suppressor status has been fully established since several studies have described the loss of ING1 and ING2 protein expression in human tumors and both ING1 and ING2 knockout mice were reported to have spontaneously developed tumors, B cell lymphomas, and soft tissue sarcomas, respectively. In this review, we will describe for the first time what is known about the ING1 and ING2 genes, proteins, their regulations in both human and mice, and their status in human tumors. Furthermore, we explore the current knowledge about identified functions involving ING1 and ING2 in tumor suppression pathways especially in the control of cell cycle and in genome stability.     

Mechanisms controlling cellular suicide: role of Bcl-2 and caspases

Apoptosis is an essential and highly conserved mode of cell death that is important for normal development, host defense and suppression of oncogenesis. Faulty regulation of apoptosis has been implicated in degenerative conditions, vascular diseases, AIDS and cancer. Among the numerous proteins and genes involved, members of the Bcl-2 family play a central role to inhibit or promote apoptosis. In this article, we present up-to-date information and recent discoveries regarding biochemical functions of Bcl-2 family proteins, positive and negative interactions between these proteins, and their modification and regulation by either proteolytic cleavage or by cytosolic kinases, such as Raf-1 and stress-activated protein kinases. We have critically reviewed the functional role of caspases and the consequences of cleaving key substrates, including lamins, poly(ADP ribose) polymerase and the Rb protein. In addition, we have presented the latest Fas-induced signalling mechanism as a model for receptor-linked caspase regulation. Finally, the structural and functional interactions of Ced-4 and its partial mam malian homologue, apoptosis protease activating factor-1 (Apaf-1), are presented in a model which includes other Apafs. This model culminates in a caspase/Apaf regulatory cascade to activate the executioners of programmed cell death following cytochrome c release from the mitochondria of mammalian cells. The importance of these pathways in the treatment of disease is highly dependent on further characterization of genes and other regulatory molecules in mammals. Received 18 February 1998; accepted February 1998     

The carbon cycle: Sources and sinks of atmospheric CO2

Summary In this contribution we try to give a synopsis of the more important processes within the global C cycle. Special attention is paid to the mechanisms by which atmospheric CO₂ is interchanged between the biosphere and the oceans, and existing qualitative and quantitative uncertainties are pointed out.     

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca²⁺-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700–841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca²⁺-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.     

2-Br-alpha-ergokryptin: influence on fertility and lactation in the rat

The effects of alpha-ergocryptin and 2-bromo-alpha-ergocryptin on fertility and lactation in rats were studied. The inhibitory actions of alpha-ergocryptin on fertility and lactation in the rat are altered differentially in the 2-bromo derivative of this ergot alkaloid. It is therefore unlikely that the fertility-inhibiting and the lactation inhibiting effects of 2-bromo-alpha-ergocryptin are governed by a single mechanism of action.     

Chromatographic purification,crystallization and study of vegetablel-alanine: 2-oxoglutarate-aminotransferase properties

Zusammenfassung l-Alanin-2 Oxoglutarataminotransferase aus Soya,Glycine hispida, wurde 230fach gereinigt und kristallisiert sowie einige physikalisch-chemische Eigenschaften (Michaelis Konstante, spezifische Wirkung, pH, Temperatureinfluss, ionale Wirkungen und Metaboliten) wurden studiert.     

2-o-Iodotyrosine]-oxytocin and [2-o-methyltyrosine]-oxytocin: basic pharmacology and comments on their potential use in binding studies

Both [2-o-iodotyrosine]-oxytocin and [2-o-methyltyrosine]-oxytocin display only weak vasopressor and antidiuretic effects on rats. They inhibit the in vitro uterotonic action of oxytocin; this inhibition is not fully competitive. It is concluded that they are not suitable as markers for studies of uterine receptor for oxytocin.     

A method for sequencing peptides: A co-operation of diphenyl phosphorazidate and 2-mercapto- or 2-hydroxypyridine for N-acyldiketopiperazine formation

Summary A new method for sequencing peptides is proposed. As a model experiment for this, Bz-Gly-Pro-OH and Bz-Gly-Sar-OH were conveniently converted to their diketopiperazine derivatives by a co-operation of diphenyl phosphorazidate and 2-mercapto- or 2-hydroxypyridine.     

Endocytosis mechanism of P2Y2 nucleotide receptor tagged with green fluorescent protein: clathrin and actin cytoskeleton dependence

Extracellular nucleotides exert a large number of physiological effects through activation of P2Y receptors. We expressed rat P2Y₂ (rP2Y₂) receptor, tagged with green fluorescent protein (GFP) in HEK-293 cells and visualized receptor translocation in live cells by confocal microscopy. Functional receptor expression was confirmed by determining [Ca²⁺]_i responses. Agonist stimulation caused a time-dependent translocation of the receptor from the plasma membrane to the cytoplasm. Rearrangement of the actin cytoskeleton was observed during agonist-mediated rP2Y₂-GFP receptor internalization. Colocalization of the internalized receptor with early endosomes, clathrin and lysosomes was detected by confocal microscopy. The inhibition of receptor endocytosis by either high-density medium or chlorpromazine in the presence of UTP indicates that the receptor was internalized by the clathrin-mediated pathway. The caveolin- mediated pathway was not involved. Targeting of the receptor from endosomes to lysosomes seems to involve the proteasome pathway, because proteasomal inhibition increased receptor recycling back to the plasma membrane.Received 8 February 2005; received after revision 18 March 2005; accepted 11 April 2005