Low molecular weight protein tyrosine phosphatases: small,but smart

Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation. Despite very limited sequence similarity to the PTP superfamily, they display a conserved signature motif in the catalytic site. LMW-PTP associates and dephosphorylate many growth factor receptors, such as platelet-derived growth factor receptor (PDGF-r), insulin receptor and ephrin receptor, thus downregulating many of the tyrosine kinase receptor functions that lead to cell division. In particular, LMW-PTP acts on both growth-factor-induced mitosis, through dephosphorylation of activated PDGF-r, and on cytoskeleton rearrangement, through dephosphorylation of p190RhoGAP and the consequent regulation of the small GTPase Rho. LMW-PTP activity is modulated by tyrosine phosphorylation on two specific residues, each of them with specific characteristics. LMW-PTP activity on specific substrates depends also on its localization. Moreover, LMW-PTP is reversibly oxidized during growth factor signaling, leading to inhibition of its enzymatic activity. Recovery of phosphatase activity depends on the availability of reduced glutathione and involves the formation of an S–S bridge between the two catalytic site cysteines. Furthermore, studies on the redox state of LMW-PTP in contact-inhibited cells and in mature myoblasts suggest that LMW-PTP is a general and versatile modulator of growth inhibition. Received 17 January 2002; received after revision 22 March 2002; accepted 26 March 2002     

Guaiacol-O-methyltransferase: A mammalian enzyme capable of forming di-O-methyl catecholamine derivatives

Résumé On a extrait et characterisé une enzyme capable de transférer aux catécholamines 4-O-méthyles le group méthyle provenant de l'S-adénosylméthionine et produire des substances diméthoxyques. Cette enzyme est active dans différents tissus de Mammifères.

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This work was supported by Public Health Service grants Nos. MH-08618 and MH-07961 and a Research Scientist's Award No. MH-14020, to A.J.F.     

Evidence of a pollen esterase capable of hydrolyzing sporopollenin

Summary The activity of an esterase is associated with the germinal pore formation of the pollen grains of barley. Cytochemical evidence is given that the enzyme is capable of hydrolyzing sporopollenin. Some staining methods new to palynological studies were introduced.Dr.J. R. Rowley is thanked for suggestions to the MS. The work was supported by the Finnish Academy and by a grant from the Eemil Aaltosen Säätiö Foundation, and from the Finnish Academy of Science.     

Are rat alveolar macrophages capable of phagocytizing pollen grains?]

Plane-tree pollen grains were incubated in vitro with alveolar macrophages from inbred Rats, and the possibility of phagocytosis was investigated. No phagocytosis was observed even after 48 hrs incubation. But alveolar cells were bound to pollen grains generally at the apertures. This binding did not require the Fc receptor on the macrophage membrane.     

Very small microspheres are useful for the determination of cardiac output but not organ blood flow in conscious rabbits

Summary Very small microspheres with a diameter of 8–10 m can be used for the measurement of cardiac output, by the reference flow method, in conscious rabbits. However, they were found not to be suitable for the determination of the distribution of cardiac output or blood flow to most organs. These small microspheres offer certain advantages for the measurement of cardiac output; the numbers required to achieve a specified accuracy of measurement are discussed.     

Labile lipophilic derivatives of norepinephrine capable of crossing the blood-brain barrier

Zusammenfassung Das in vivo leicht hydrolysierbare 0, 0, 0-Triacetat und das zyklische Brenzkatechin-carbonat desl-Noradrenalins setzen im Herzen der Maus tritiiertes Noradrenalin frei. Beide Derivate sowie das 0, 0, 0-Trimethylsilyl-l-noradrenalin-7-³H, sind genügend lipophil, um leicht die Liquorschranke zu überschreiten, wo sie im Zentralnervensystem langsam tritiiertes Noradrenalin freisetzen. Solche Noradrenalin-Depot-Derivate sind möglicherweise von therapeutischem Interesse.     

Demonstration of a soluble factor capable of inhibiting allogenic lymphocyte proliferation in man]

During the secondary mixed lymphocyte reaction (MLR), i.e. after the double in vitro allogenic sensitization between responding and stimulating cells bearing at least one HLA-DR incompatibility, suppressor cells are developed [1]. They are able to inhibit a primary MLR provided that the stimulating cells possess the same DR incompatibility as the immunizing cells. We report here that this inhibition is due to the production by these cells of a soluble suppressor factor which acts on responding cells provided that they share at least one gene product of the HLA-D region with the cells producing the factor. This a feedback process of auto-inhibition occurring after hyperimmunization. The action of this suppressor factor seems to be genetically restricted to an as yet unknown locus in linkage disequilibrium with HLA-DR.     

Modulating RNA structure and catalysis: lessons from small cleaving ribozymes

RNA is a key molecule in life, and comprehending its structure/function relationships is a crucial step towards a more complete understanding of molecular biology. Even though most of the information required for their correct folding is contained in their primary sequences, we are as yet unable to accurately predict both the folding pathways and active tertiary structures of RNA species. Ribozymes are interesting molecules to study when addressing these questions because any modifications in their structures are often reflected in their catalytic properties. The recent progress in the study of the structures, the folding pathways and the modulation of the small ribozymes derived from natural, self-cleaving, RNA motifs have significantly contributed to today’s knowledge in the field.     

Coronavirus envelope protein: A small membrane protein with multiple functions

Coronavirus envelope protein is a small membrane protein and minor component of the virus particles. It plays important roles in virion assembly and morphogenesis, alteration of the membrane permeability of host cells and virus-host cell interaction. Here we review recent progress in characterization of the biochemical properties, membrane topology and functions of the protein. Received 27 February 2007; received after revision 4 April 2007; accepted 26 April 2007