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J Forsman

Publications and source records attributed to J Forsman.

3 recordsLinked to original sources
PubMed1997

LETTER TO THE EDITOR

The solvation force between two planar surfaces immersed in a model liquid mimicking water is obtained using Monte Carlo computer simulations and free energy functional theory calculations. When the surfaces are hydrophilic, the solvation force is repulsive, as is the net force, provided the solvent-surface interaction is strong, compared with the surface-surface and solvent-solvent interactions. The range of the surface-solvent interaction is shown to have a profound influence on the resulting solvation force, whereas solvent orientational order is only of minor importance. We conclude that a repulsive force would also be found in a less polar solvent, confined between sufficiently solvophilic surfaces. With hydrophobic surfaces, the solvation force is attractive. The net lowering of solvent density between the surfaces increases the attraction beyond the expected van der Waals interaction. This density depression contribution is substantial even at rather large separations and will be present for all fluids confined between solvophobic surfaces. Our calculations suggest that the famous "hydrophobic force" is often dominated by density depression. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1994

p42 mitogen-activated protein kinase and p90 ribosomal S6 kinase are selectively phosphorylated and activated during thrombin-induced platelet activation and aggregation.

Human platelets provide an excellent model system for the study of phosphorylation events during signal transduction and cell adhesion. Platelets are terminally differentiated cells that exhibit rapid phosphorylation of many proteins upon agonist-induced activation and aggregation. We have sought to identify the kinases as well as the phosphorylated substrates that participate in thrombin-induced signal transduction and platelet aggregation. In this study, we have identified two forms of mitogen-activated protein kinase (MAPK), p42mapk and p44mapk, in platelets. The data demonstrate that p42mapk but not p44mapk becomes phosphorylated on serine, threonine, and tyrosine during platelet activation. Immune complex kinase assays, gel renaturation assays, and a direct assay for MAPK activity in platelet extracts all support the conclusion that p42mapk but not p44mapk shows increased kinase activity during platelet activation. The activation of p42mapk, independently of p44mapk, in platelets is unique since in other systems, both kinases are coactivated by a variety of stimuli. We also show that platelets express p90rsk, a ribosomal S6 kinase that has previously been characterized as a substrate for MAPK. p90rsk is phosphorylated on serine in resting platelets, and this phosphorylation is enhanced upon thrombin-induced platelet activation. Immune complex kinase assays demonstrate that the activity of p90rsk is markedly increased during platelet activation. Another ribosomal S6 protein kinase, p70S6K, is expressed by platelets but shows no change in kinase activity upon platelet activation with thrombin. Finally, we show that the increased phosphorylation and activity of both p42mapk and p90rsk does not require integrin-mediated platelet aggregation. Since platelets are nonproliferative cells, the signal transduction pathways that include p42mapk and p90rsk cannot lead to a mitogenic signal and instead may regulate cytoskeletal or secretory changes during platelet activation.

Blood Platelets↗