Human stereovision without localized image features

Many theories of human stereovision are based on feature matching and the related correspondence problem. In this paper, we present psychophysical experiments indicating that localized image features such as Laplacian zerocrossings, intensity extrema, or centroids are not necessary for binocular depth perception. Smooth one-dimensional intensity profiles were combined into stereograms with mirror-symmetric half-images such that these localized image features were either absent or did not carry stereo information. In a discrimination task, subjects were asked to distinguish between stereograms differing only by an exchange of these half-images (ortho- vs. pseudoscopic stereograms). In a depth ordering task, subjects had to judge which of the two versions appeared in front. Subjects are able to solve both tasks even in the absence of the mentioned image features. The performance is compared to various possible stereo mechanisms. We conclude that localized image features and the correspondences between them are not necessary to perceive stereoscopic depth. One mechanism accounting for our data is correlation or mean square difference. Received: 8 February 1994 / Accepted in revised form: 15 September 1994     

The stable bacteriocin release protein signal peptide, expressed as a separate entity, functions in the release of cloacin DF13

Abstract The pCloDF1S encoded bacteriocin release protein (BRP) plays a role in the release of the bacteriocin cloacin DF13. The BRP signal peptide is stable after cleavage, and accumulates in the cytoplasmic membrane. A BRP which is correctly targeted by the unstable murein lipoprotein signal peptide (Lpp-BRP) is not capable of inducing the release of cloacin DF13. To investigate the role of the stable BRP signal peptide in the release of cloacin DF13, the stable BRP signal peptide and the Lpp-BRP were expressed in trans in cells also producing cloacin DF13. Expression and release experiments indicate that the stable signal peptide can complement the Lpp-BRP in the release of cloacin DF13.     

Chromatographic resolution of some cyclic sulfoximides derived from prochiral and chiral sulfoxides

Three endocyclic sulfoximides of the 1-aryl- and 1-alkyl-3-oxo-benzo[d]-isothia (IV)-azole 1-oxide type (1-substituent = 2′-carboxyphenyl, 2′-carbethoxyphenyl, and octyl, respectively) were found to be well resolved on a chiral phase derived from bovine serum albumin (BSA). Selectivities (α) of 1.74, 1.12, and 1.44, respectively, were obtained. The retention behaviour of 1-octyl-3-oxo-benzo[d]isothia(IV)-azole 1-oxide was further investigated in some detail as a function of the mobile phase composition and the elution order was established from optically active material obtained from the enantiopure sulfoxide precursor. An enantiomeric excess of 85.4% was obtained in the cyclocondensation reaction of the octyl-substituted sulfoxide precursor with hydrazoic acid to the corresponding endocyclic sulfoximide. © 1995 Wiley-Liss, Inc.     

Crystalline aggregation of a proteolytic fragment of the major head protein of bacteriophage T4.

An analysis has been made of the composition and structure of the two types of sheets assembled from material from dissociated bacteriophage T2 (Poglazov &; Mesyhanzhinov, 1967) and T4 capsids. Serological techniques have been used to show that both types of sheet are assembled from proteolytic fragment of P23¹, the major capsid constituent. The two types of sheets have been found to interconvert depending on the concentration of Mg²⁺ ions in the buffer. Computer modelling experiments show that the “hexagonal” and “rectangular” morphologies observed in the negative stain are due to in-register and staggered associations, respectively, of a single basic hexagonal lattice. Analysis by polyacrylamide gel electrophoresis of samples of sheets and dissociated capsids, together with previous results from immune electron microscopy (Kistler et al., 1978), suggest that hexamers of the proteolytic fragment are derived conservatively from capsomers of the phage head.The value of this proteolytic P23 fragment has been twofold: (1) it has proved to be a useful peptide in the ongoing primary sequence determination of P23 and (2) antibodies raised against it have been employed to follow the fate of P23 antigenic sites during various steps of phage capsid maturation (Kistler et al., 1978).     

Mutagen-induced sister chromatid exchange rate in Bloom syndrome remains unaltered in the presence of Bloom corrective factor

Summary Fibroblasts of a patient with Bloom syndrome (GM-1492) were cultured in the presence of either mitomycin C, ethylmethanesulfonate, or 4-nitroquinoline-1-oxide, (4-NQ1-O) and sister chromatid exchange was determined. The mutagens enhanced the sister chromatid exchange rate to different degrees, 4-NQ1-O being the most potent substance. Bloom corrective factor, which is present in normal cell-conditioned culture medium, reduced the spontaneously increased SCE in Bloom syndrome cells by about 20 SCE per metaphase but failed to reduce the additional mutagen-induced SCE increase. These findings indicate that only spontaneously, but not mutagen-indeuced, SCE in Bloom syndrome fibroblasts can be decreased by the Bloom corrective factor.     

Identification of pristanoyl-CoA oxidase as a distinct, clofibrate non-inducible enzyme in rat liver peroxisomes.

In this paper we describe the identification of pristanoyl-CoA oxidase activity in rat liver peroxisomes. This activity was not stimulated by clofibrate feeding. Furthermore, the activity was found in multiple tissues. These results show that pristanoyl-CoA oxidase is different from any of the known oxidases which include a clofibrate-inducible acyl-CoA oxidase and the recently identified cholestanoyl-CoA oxidase. Gelfiltration and chromatofocusing experiments provide conclusive evidence that we are dealing with a novel acyl-CoA oxidase with a unique function in peroxisomal beta-oxidation.     

Differential expression of transforming growth factor-beta 1, -beta 2, and -beta 3 by glioblastoma cells, astrocytes, and microglia.

The type beta transforming growth factors (TGF) are potent regulators of the growth and functions of lymphocytes and macrophages. Recently the human glioblastoma cell line 308 was shown to produce TGF-beta 2. The relevance of this finding was evaluated further by comparing human glioblastoma cells with their nontransformed animal counterpart, astrocytes, with regard to the production of the three TGF-beta isoforms observed so far in mammals. In this report astrocytes are demonstrated to secrete also TGF-beta 2 and to express TGF-beta 1, -beta 2, and -beta 3 mRNA in vitro. In contrast, cultured murine brain macrophages release TGF-beta 1 and are positive for TGF-beta 1 mRNA only. Glia cell-derived TGF-beta 1 and -beta 2 are detected in latent form whereas both latent and active TGF-beta are identified in the supernatant of three human glioblastoma cell lines tested. These cell lines, however, show heterogeneity in regard to the isoform of TGF-beta expressed but share with astrocytes the inability to release TGF-beta 3. Provided production and activation of latent TGF-beta occur in vivo, astrocytes and microglia may then be expected to exert regulatory influences on immune mediated diseases of the central nervous system.     

Mechanistic coupling of transport and phosphorylation activity by enzyme IImtl of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system

Mannitol bound to enzyme IImtl could be trapped specifically by rapid phosphorylation with P-HPr. The assay was used to demonstrate transport of mannitol across the cytoplasmic membrane with and without phosphorylation of mannitol. The latter was 2-3 orders of magnitude slower. The fraction of bound mannitol molecules that was actually phosphorylated, the efficiency of the trap, was less than 50%. The efficiency was not very different for enzyme IImtl embedded in the membrane of vesicles with an inside-out orientation or solubilized in detergent. Subsequently, it is argued that the fraction of the bound mannitol molecules that was not phosphorylated dissociated into the cytoplasmic space. A model for the catalytic mechanism of enzyme IImtl is proposed on the basis of interpretations of the present experiments. The main features of the model are the following: (i) mechanistically, the coupling between transport and phosphorylation is less than 50%; (ii) in the physiological steady state of mannitol transport and metabolism, the coupling is 100%; (iii) phosphorylated enzyme IImtl catalyzes facilitated diffusion at a high rate; (iv) the state of phosphorylation of the cytoplasmic domain modulates the activity of the translocator domain; (v) the enzyme catalyzes phosphorylation of free cytoplasmic mannitol at least as fast as it catalyzes transport plus phosphorylation of free periplasmic mannitol.     

Continuous culture of suspended plant cells

Summary Continuous culture is an attractive research tool in physiologic and growth and production kinetics research. However, fulfillment of the basic assumptions of continuous culture in the experimental set-up may cause problems. The homogeneity of plant cell cultures and effluent, particularly, may cause problems. This paper presents an experimental set-up which solves these problems and describes the use of this equipment in a study of the growth kinetics of plant cells. Industrial application of the continuous culture of plant cells in the production of secondary metabolites seems to be profitable when compared with batch or fed-batch cultures. However, various problems such as uncoupled product formation and strain instability make fed-batch culture a better choice. Presented in the Session-in-Depth Batch Production and Fermentation at the 1991 World Congress on Cell and Tissue Culture, Anaheim, California, June 16–20, 1991.     

Fluorescence investigation of the sex steroid binding protein of rabbit serum: steroid binding and subunit dissociation

The relationship between steroid binding and protein subunit interactions of rabbit sex steroid binding protein (rSBP) has been studied by steady-state and time-resolved fluorescence spectroscopy. The high-affinity (Ka approximately 10(8) M-1 at 4 degrees C), fluorescent estrogen d-1,3,5(10),6,8-estrapentaene-3,17 beta-diol [dihydroequilenin (DHE)] was used as a fluorescent probe of the steroid-binding site. Perturbation of the binding site with guanidinium chloride (Gdm.Cl) was monitored by changes in the steady-state fluorescence anisotropy of DHE as well as by changes in fluorescence quenching of DHE with acrylamide. The results of acrylamide quenching at 11 degrees C show that, while between 0 and 1 M Gdm.Cl the steroid-binding site is completely shielded from bulk solvent, there is decreased DHE binding. To study the subunit-subunit interactions, rSBP was covalently labeled with dansyl chloride in the presence of saturating 5 alpha-dihydrotestosterone (DHT), which yielded a dansyl-conjugated protein that retained full steroid-binding activity. The protein subunit perturbation was monitored by changes in the steady-state fluorescence anisotropy of the dansyl group. At 11 degrees C, the dansyl anisotropy perturbation, reflecting changes in global and segmental motions of the dimer protein, occurs at concentrations of Gdm.Cl above 1 M. The Gdm.Cl titration in the presence of steroids with equilibrium association constants less than 10(8) M-1 shows a plateau near 3 M Gdm.Cl at 11 degrees C; at this Gdm.Cl concentration, no DHE is bound. No plateau is observed at 21 degrees C. At higher Gdm.Cl concentrations, the dansyl fluorescence anisotropy decreases further and shows no steroid dependence. Recovery of steroid-binding activity (assayed by saturation binding with [3H]DHT), under renaturation conditions, is dependent on both steroid concentration and affinity. Both unlabeled and dansyl-labeled protein recovery the same amount of activity, and according to fluorescence anisotropy, dansyl-labeled rSBP re-forms a dimer upon dilution below 1 M or removal of Gdm.Cl. From the steroid requirement for recovery of steroid-binding activity, it appears that a conformational template is required for the dimeric protein to re-form a steroid-binding site with native-like properties.