Spatial interactions in rapid pattern discrimination

We measured reaction times (RTs) for identification of a target among distracters under stabilized image conditions in which the positions of the target and the distracters were constant within a single experimental session. Under these conditions, the observer need not search for the target because its position is known. We nevertheless found that the presence of even a single distracter could elevate RTs. The magnitude of this effect depended on the distance of the distracter from the target and, for some observers, the distance of the distracter from the fovea. When we added not one but six background elements in a ring around the target, RT increased even more. If, apart from these neighboring distracters, the target was surrounded by more distracters located beyond the nearest neighbors, RT was, in general, not increased further. These findings suggest that adding background elements in a search task can elevate RTs in ways that are not dependent on the positional uncertainty of the target.     

Aliphatic hydrocarbons obtained from iron carbides: Possible stellar and meteoritic implications

Origins of Life and Evolution of Biospheres -     

Protein kinase C phosphorylates the sponge aggregation receptor after its binding to the homologous aggregation factor

The aggregation factor from the sponge Geodia cydonium functions also as a growth factor after binding to the aggregation receptor (= growth factor receptor) on the plasma membrane of homologous cells. We have recently shown that protein kinase C is involved in the pathway transducing the growth factor signal. Here we report that the aggregation receptor (a polypeptide with an Mr of 43,500) is phosphorylated by protein kinase C. Using a plasma membrane fraction only this phosphoprotein (pp) 43.5 became phosphorylated by kinase C. The phosphorylation of pp43.5 in intact cells in response to the binding of the aggregation factor to this polypeptide was a late event and occurred 10 to 15 h after addition of the aggregation factor. Based on studies with phorbol esters it appears to be very likely that protein kinase C also phosphorylates pp43.5 in vitro. The degree of phosphorylation of pp43.5 paralleled with both the extent of DNA synthesis and ras oncogene expression. The latter process resulted in a switch of the responsiveness of the cells to growth factors signals: 10 to 15 h after addition of the aggregation factor to dissociated cells, this factor lost its growth factor function while the homologous lectin gained the ability to stimulate cell proliferation (to be published). These results support the idea that phosphorylation of pp43.5 (= aggregation receptor) results in an inhibition of its function, i.e., the transduction of the growth factor (= aggregation factor) signal.     

Use of regularly structured bacterial cell envelope layers as matrix for the immobilization of macromolecules

Summary Carboxyl groups present on the outer face of the hexagonally ordered S-layer lattices from Bacillus stearothermophilus PV72 and Clostridium thermohydrosulfuricum L111-69 were activated with carbodiimide. The reaction of the activated carboxyl groups with free amino groups of low molecular weight nucleophiles was controlled by labelling with polycationized ferritin, a net positively charged topographical marker for electron microscopy, which densely binds to S-layers possessing free carboxyl groups. Carbodiimide-activated carboxyl groups were also allowed to react with amino groups of ferritin (MW 440 000) and invertase (MW 270 000). Covalent attachment of ferritin was examined by electron microscopy. Using invertase, approximately 1 mg enzyme was bound per mg S-layer protein indicating a high packing density of invertase molecules on the outer face of the S-layer lattice. The immobilized invertase retained 70% of its original activity.     

Isolation, characterization and immunological determination of basement membrane-associated heparan sulfate proteoglycan

Basement membrane-associated heparan sulfate proteoglycan (HSPG) was extracted from isolated porcine glomerular basement membranes and purified by ion-exchange chromatography. The proteogycan was characterized by specific enzymatic digestions, by amino-acid analysis, by SDS-polyacrylamide gel electrophoresis and by density gradient centrifugation. Polyclonal antibodies were raised against the purified HSPG in rabbits. Antibodies were characterized by enzyme immunoassays, immunoprecipitation and immunohistological methods. They were shown to recognize specifically the core protein of HSPG from porcine, human and rat glomerular basement membrane but did not recognize HSPG from guinea pig or rabbit kidney. The affinity-purified antibodies did not cross-react with other basement membrane proteins like laminin, fibronectin or collagen type IV nor with chondroitin sulfate-rich or keratan sulfate-rich proteoglycans from human or bovine tissue. Using these antibodies an enzyme immunoassay was developed for determination of HSPG in the range of 1-100 ng/ml. Studies with cultured porcine endothelial cells showed that subendothelial basement membrane-associated HSPG may be determined with the enzyme immunoassay.     

Accuracy of routine flow-cytometric bitmap selection for three leukocyte populations

A double-blind study was performed with peripheral blood of 41 human subjects to check the accuracy of determination of lymphocyte, monocyte, and granulocyte windows with which every flow cytometric analysis of leukocyte markers starts. White blood cell suspensions were prepared according to the whole blood method and analyzed on an EPICS-C flow cytometer using the two-parameter 90 degrees light scatter vs. forward angle light scatter (granularity vs. cell size) data distribution. Windows (bitmaps) for lymphocytes, monocytes, and granulocytes were drawn and numbers of cells determined in each. The proportions of lymphocytes, monocytes, and granulocytes were calculated in relation to total cell number, counted and in relation to the sum of cells in three bitmaps, and then compared with proportions determined by microscopic whole blood cell (WBC) differential and a WBC differential determined in an automated hematology analyzer. Average proportions of lymphocytes obtained by the flow cytometer were significantly lower than those obtained by either microscopic or automated differential, suggesting that some of the relevant cells were not included in the bitmaps. Granulocyte proportion related to total cell number was lower and that related to bitmap cell number higher than that obtained by microscopic and automatic differentials, suggesting that nongranulocytic cells were included in the granulocyte bitmaps. Proportions of lymphocytes and granulocytes obtained by the flow cytometer correlated well with those obtained by both microscopic and automatic differential. In contrast, the proportions of monocytes showed a poor correlation, which is probably due to their low number and delicate position in the distribution, and which makes them difficult to delineate.     

Plasmid cloning vectors replicating in Escherichia coli,amino acid-producing coryneform bacteria and Methylobacillus sp.

Summary Four hybrid plasmids were constructed from the cryptic plasmid pAM330 (from Brevibacterium lactofermentum; 4.5 kb) and the broadhost-range plasmid pGV1106 (9.0 kb; Km^r Sm^r) isolated from Escherichia coli. All of them were mobilized from E. coli into the Gram-negative methylotrophic bacterium Methylobacillus sp. and two of these constructs (pCEM300 and pCEM400) were transferred by transformation into B. flavum and Corynebacterium glutamicum. Their kanamycin-resistance determinant coming from Gram-negative hosts was expressed in these Gram-positive bacteria. Both pCEM300 and pCEM400 are very stably maintained in B. flavum and represent suitable vectors for gene cloning in coryneform producers of amino acids.     

Effect of electric stimulation of the caudate nucleus on the foci of epileptic activity in the cerebral cortex

It was shown in the acute experiments on rats that caudate nucleus is one of the main structures of brain antiepileptic system. It was noted that reduction of the influence of activating cerebral structures is a tool for abolishing the proepileptic effects which occur in some cases under conditions of electrical stimulations of neostriatum. Results of the investigation confirm G. N. Kryzhanovsky theory of a role of system-antisystem interrelations in suppression of neuropathological syndromes as a result of system hyperactivity.