Transmembrane interactions and the mechanisms of transport of proteins across membranes

We have made observations, by double fluorescence staining of the same cell, of the distributions of surface receptors, and of intracellular actin and myosin, on cultured normal fibroblasts and other flat cells, and on lymphocytes and other rounded cells. The binding of multivalent ligands (a lectin or specific antibodies) to a cell surface receptor on flat cells clusters the cell receptors into small patches, which line up directly over the actin- and myosin-containing stress fibers inside the cell. Similar ligands binding to rounded cells can cause their surface receptors to be collected into caps on the surface, and these caps are invariably found to be associated with concentrations of actin and myosin under the capped membrane. Although these ligand-induced surface phenomena appear to be different on flat and rounded cells, we propose that in both cases clusters of receptors become linked across the membrane to actin- and myosin-containing structures. In flat cells these structures are very long stress fibers; therefore, when clusters of receptors become linked to these fibers, the clusters are immobilized. In round cells, membrane-associated actin- and myosin-containing structures are apparently much less extensive than in flat cells; therefore, clusters of receptors linked to these structures are still mobile in the plane of the membrane. We suggest that in this case the clusters are then actively collected into a cap by an analogue of the muscle sliding filament mechanism. To explain the transmembrane linkage, we propose that actin is associated with the plasma membrane as a peripheral protein which is directly or indirectly bound to an integral protein (or proteins) X of the membrane. Individual molecules of any receptor are not bound to X, but after they are specifically clustered into patches, a patch of receptors then becomes bound to S and hence to actin/myosin. Patching and capping of specific receptors on rounded cells is often accompanied by a specific endocytosis of the ligand-receptor complexes. This represents one common transport mechanism of a protein (the ligand) across the plasma membrane. The possibility is discussed that this type of endocytosis is mediated by a transmembrane linkage of the clustered receptor to actin/myosin. Another mechanism of endocytosis involves the “coated pit” structures that are observed by electron microscopy of plasma membranes. The possible relationships between an actin/myosin and a coated pit mechanism of endocytosis are explored.     

Preparation and use of insolubilized amyloglucosidase for the production of sweet glucose liquors

Amyloglucosidase (EC. 3.2.1.3), partially purified from an Aspergillus species, was chemically attached to DEAE cellulose using the bifunctional reagent 2-amino-4,6-dichloro-s-triazine. The action of the insolubilized enzyme derivative on dilute maltose and dextrin solutions was studied in a packed bed. A second and deeper bed was used to demonstrate the possibility of a continuous process for raising the dextrose; equivalents of “glucose” liquors of high concentration formed by acid hydrolysis of maize starch.     

The influence of dissolved oxygen partial pressure on the level of various enzymes in mouse LS cells

The intracellular levels of seven enzymes in mouse LS cells growing in suspension culture at controlled dissolved oxygen partial pressures (pO₂) have been measured. During the growth of each culture large fluctuations were observed in the levels of some enzymes, particularly aldolase and cytochrome oxidase. Mean values for the concentration of each enzyme during the growth phase have been calculated. These results are discussed in relation to previous observations made on the growth of mouse LS cells.     

IND-enzymes: a repository for hydrolytic enzymes derived from thermophilic and psychrophilic bacterial species with potential industrial usage

Extremophiles - Biocatalysts provide many advantages over the traditional chemically assisted processes prevalent in industries. Consequently, the search for novel enzymes has increased over the...     

Electrical activity in frog heart after isoproterenol

The electrical and mechanical activity of myocardial strips from Rana pipiens after injection of isoproterenol (ISO) was studied during cyanide anoxia. Compared to controls, isometric tension was more depressed, resting tension more increased and action potential duration extremely reduced when ISO-damaged heart was exposed to cyanide anoxia. The same results could be obtained after inactivation of the fast Na+-system, when the resting membrane potential was held at -50 mV in elevated Ko+. These alterations are explained by an increase of Cai2+ since cyanide is known to release intracellularly stored Ca2+. Pretreatment with ISO may possibly increase the amount of releasable Ca2+.