Distribution of prohormone convertase-6 expression in the gastrointestinal tract and effects of a fasting-refeeding regimen and a high-fat diet on ileal prohormone convertase-6 expression

Proforms of gastrointestinal peptide hormones and neuropeptides are processed, in part, by prohormone convertases (PCs) to mature, biologically active peptides. The purpose of this study was to characterize the mRNA levels of PC-6 isoforms, PC-6A and PC-6B, in the gastrointestinal tract and pancreas of the rat, and to investigate the effects of a fasting and refeeding regimen, and a high-fat diet on ileal PC-6A expression. PC-6A mRNA is expressed throughout the entire gastrointestinal tract with the highest levels in the small intestine. Multiple-sized transcripts are present. PC-6B mRNA is expressed in the antrum and fundus of the stomach, in the small intestine, and colon. Ileal PC-6A mRNA expression increases significantly with fasting and then declines with refeeding toward control levels. Increased dietary fat increases PC-6A mRNA levels in the ileum. Since PC-6 is found throughout the entire gastrointestinal tract, it is likely that PC-6 participates in the processing of proforms of gastrointestinal peptides. The two isoforms of PC-6 have different patterns of distribution in the gastrointestinal tract and pancreas, suggesting that they process proforms of different gut peptides.

[The role of CDDP on cytotoxicity of TILs obtained from colorectal tumors]

The effects of intravenous injection of cisplatin (CDDP) and the incubated with CDDP in vitro on the epitopes and cytotoxicity of TIL obtained from eight colorectal tumor patients were detected respectively by flow cytometer. There was a significant increase in CD3+/CD8+ subset in TIL in patients receiving intravenous injection of CDDP. And the cytotoxicity of these TILs increased significantly. The cytotoxities were positively correlated with the amount of CD3+/CD8+ subset in TIL. Raji cells incubated with CDDP in vitro showed increased susceptibility to TIL induced lysis.

Increase of manganese superoxide dismutase, but not of Cu/Zn-SOD, in experimental optic neuritis

PURPOSE

To evaluate the role of manganese superoxide dismutase (Mn-SOD) and copper/zinc superoxide dismutase (Cu/Zn-SOD) in cellular protection of the optic nerve against the oxidative injury that contributes to demyelination in experimental allergic encephalomyelitis (EAE).

METHODS

Immunocytochemistry for Mn-SOD and Cu/Zn-SOD and ultracytochemical localization of hydrogen peroxide (H2O2) were performed on the optic nerves of guinea pigs with EAE and normal guinea pigs. Cell-specific enzyme expression of SOD was quantitated by computerized morphometric analysis.

RESULTS

Light microscopy showed a perivascular distribution of Mn-SOD-positive cells in the optic nerves of animals with EAE. Electron microscopy showed that the Mn-SOD immunogold was confined exclusively to mitochondria, whereas Cu/Zn-SOD immunogold was found in the cytoplasmic matrix and nucleus of cells of the optic nerve in both animals with EAE and normal animals. Results of quantitative analysis of the optic nerves of animals with EAE showed an 8-fold increase in Mn-SOD immunogold in astroglial cells and a 13-fold increase in microglial/phagocytic cells in comparison with that of normal animals. Increases in Mn-SOD immunogold were contiguous to H2O2-derived reaction product. No increases in Cu/Zn-SOD immunogold were detected in EAE.

CONCLUSIONS

Increases in Mn-SOD activity in astroglial cells and microglial/phagocytic cells may contribute to the relative sparing of these cells from injury in EAE, whereas the low level of Mn-SOD in oligodendroglial cells and axons may increase their vulnerability to the effects of superoxide-induced oxidative injury that results in demyelination.

Development of AFLP markers in barley

To investigate the application of amplified fragment length polymorphism (AFLP) markers in barley, 96 primer combinations were used to generate AFLP patterns with two barley lines, L94 and Vada. With seven primer combinations, only a few intense bands were obtained, probably derived from repeated sequences. With the majority of the remaining 89 primer combinations, on average about 120 amplification products were generated, and the polymorphism rate between the two lines was generally over 18%. Based on the number of amplified products and the polymorphism rate, the 48 best primer combinations were selected and tested on 16 barley lines, again including L94 and Vada. Using a subset of 24 primer combinations 2188 clearly visible bands within the range from 80 to 510 bp were generated; 55% of these showed some degree of polymorphism among the 16 lines. L94 versus Vada showed the highest polymorphism rate (29%) and Proctor versus Nudinka yielded the lowest (12%). The polymorphism rates per primer combination showed little dependence on the barley lines used. Hence the most efficient and informative primer combinations identified for a given pair of lines turned out to be highly efficient when applied to others. Generally, more than 100 common markers (possibly locus specific) among populations or crosses were easily identified by comparing 48 AFLP profiles of the parent lines. The existence of such a large number of markers common to populations will facilitate the merging of molecular marker data and other genetic data into one integrated genetic map of barley.

Influence of nicotine on gastrin and peptide YY in the rat

The objective of this study was to examine the effects of nicotine and high-fat diets on gastrin and peptide YY (PYY) homeostasis in the rat. Antral levels of gastrin mRNA and peptide and ileal and colonic levels of PYY mRNA and peptide were examined. Serum levels of gastrin in response to food were also measured. Control rats were ad-lib fed or pair-fed according to the daily food intake of nicotine-treated rats. The results of this study indicate that nicotine treatment and fat diets can influence gastrin and PYY gene expression in the gastrointestinal tract.

Basal phosphorylation of the PEST domain in the I(kappa)B(beta) regulates its functional interaction with the c-rel proto-oncogene product

The product of the c-rel proto-oncogene (c-Rel) belongs to the NF-kappaB/Rel family of polypeptides and has been implicated in the transcriptional control of cell proliferation and immune function. In human T lymphocytes, c-Rel is sequestered in the cytoplasmic compartment by constitutively phosphorylated inhibitors, including I(kappa)B(alpha) and I(kappa)B(beta). Studies with bacterially expressed forms of these inhibitory proteins revealed that unphosphorylated I(kappa)B(alpha) but not I(kappa)B(beta) assembles with c-Rel and inhibits its DNA binding activity. Furthermore, latent I(kappa)B(beta)-c-Rel complexes derived from mammalian cells were sensitive to phosphatase treatment, whereas I(kappa)B(alpha)-c-Rel complexes were resistant. We have identified a constitutive protein kinase in unstimulated T cells that associates with and phosphorylates I(kappa)B(beta) in vitro. The substrate specificity, electrophoretic mobility, and antigenic properties of this I(kappa)B(beta)-associated kinase (BAK) suggest identity with casein kinase II (CKII), an enzyme known to mediate basal phosphorylation of I(kappa)B(alpha). Phosphorylation of recombinant I(kappa)B(beta) by either BAK or CKII restored the capacity of this inhibitor to antagonize the DNA binding activity of c-Rel. Peptide mapping and mutational analyses localized the bulk of the basal phosphorylation sites in I(kappa)B(beta) to the C-terminal PEST domain, which contains two potential acceptors for CKII-mediated phosphoryl group transfer (Ser-313 and Ser-315). Point mutations introduced into the full-length inhibitor at Ser-313 and Ser-315 led to a significant reduction in the phosphorylation of I(kappa)B(beta) and severely impaired its c-Rel inhibitory function in vivo. Taken together, these findings strongly suggest that basal phosphorylation of the PEST domain of I(kappa)B(beta) at consensus CKII sites is required for the efficient formation of latent I(kappa)B(beta)-c-Rel complexes.

Beta-adrenergic responsiveness of papillary muscles in the rat postinfarction model

Rats in which ligation of the left anterior descending (LAD) coronary artery did not result in an infarct visible to the naked eye have generally been called sham-operated controls and have been used to evaluate changes in the characteristics of the remaining viable myocardium of rats where myocardial infarction was present. Whether these sham-operated rats are equivalent to normal controls or whether they have been altered by the surgery is unknown. The purpose of this study was to evaluate potential differences in papillary muscle mechanical characteristics and responsiveness to beta-adrenergic stimulation in control, open-chest, sham-operated (aborted infarct), and infarct rats 4 weeks after surgery. Absence of significant myocardial damage was verified by morphologic examination in sham-operated hearts: myocardial infarction scar was 1.5 +/- 0.6% (mean +/- SE) of circumference, no infarct being transmural. Basal contractile indices were decreased in papillary muscles in infarct rats compared with the three other groups. The response in contractile indices of infarct muscles to isoproterenol was also less compared with the other three groups. However, although basal contractility was the same in muscles from sham-operated, open-chest, and controls, the responsiveness of sham-operated muscles to isoproterenol was less: change in total tension of 2.9 +/- 1.2% vs. 9.5 +/- 2.7% for controls and 9.3 +/- 2.4% for open-chest (p < 0.05). Percent change in maximum rate of tension development (+dT/dt) was also less in muscles from sham-operated versus control muscles (21 +/- 2 vs. 33 +/- 6%; p < 0.05). Twitch configuration changed similarly with isoproterenol in all four groups. Thus, although contractility is unaffected by sham operation, beta-adrenergic responsiveness of tension-generating indices is modified.

Growth hormone upregulates gastrin and peptide YY gene expression

The purpose of these studies was to examine the effects of excess growth hormone (GH) on gastrin and peptide YY (PYY) gene expression. Transgenic mice with the bovine GH gene linked to a mouse metallothionein I promoter were used as a model of chronic GH excess. Antral gastrin mRNA and peptide levels were elevated significantly (P < 0.05) in GH transgenic mice compared with wild type littermates. Ileal PYY mRNA and ileal and colonic PYY levels were significantly elevated in GH transgenic mice compared with wild type littermates. The elevations in gastrin and PYY gene expression in GH transgenic mice were independent of food intake. Serum concentrations of gastrin and PYY were also elevated in GH transgenic mice. Immunohistochemical analysis showed that the density of PYY-containing cells in the colon of GH transgenic mice and wild type littermates did not differ. In addition, the mRNA and protein levels of chromogranin A, a marker of endocrine cells, were not increased in the colon of GH transgenic mice. Together, these data indicate that GH, insulin-like growth factor I, or both can upregulate gastrointestinal gastrin and PYY gene expression directly.

[A study on red blood cell immune function in patients with Guillain-Barré syndrome and multiple sclerosis]

In order to understand whether there is red blood cell (RBC) immune dysfunction and the relationship between RBC immune abnormality and clinical state in patients with multiple sclerosis (MS) and Guillain-Barré syndrome (GBS), RBC immune function and circulation immune complex (CIC) level were evaluated in patient with these two diseases by using RBC immune adhesion test. It was found that the rate of formation of red blood cell-C3b receptor-yeast rosette was significantly lower in patients with these two diseases before and after treatment than that in a control group (P < 0.01). The rate of formation of red blood cell-immune complex-yeast rosette and the CIC level in GBS group were notably higher than that in the control group (P < 0.05). Moreover, we observed that the immune functions in patients with severe GBS and active MS were different from those in patients with mild GBS and stable MS and the change of each immune index in GBS and MS patients was related with the degree of recovery and the clinical state. These results suggested that decreased capability of RBC immune adhesion in patients with GBC and MS may be one of factors causing these diseases.

Proteolytic processing patterns of prosaposin in insect and mammalian cells

Prosaposin is a multifunctional protein encoded at a single locus in humans and mice. The precursor contains, in tandem, four glycoprotein activators or saposins, termed A, B, C, and D, that are essential for specific glycosphingolipid hydrolase activities. Prosaposin appears to be a potent neurotrophic factor. To explore the proteolytic processing from prosaposin to mature activator proteins, metabolic labeling was done with human prosaposin expressed in insect cells, human fibroblasts, neuronal stem cells (NT2) and retinoic acid-differentiated NT2 neurons. In all cell types, the major processing pathway was through a tetrasaposin, A-B-C-D, from which saposin A was then removed. In mammalian cells monosaposins were derived from the trisaposin B-C-D by cleavage to the disaposins, B-C and C-D, that were processed to monosaposins. In insect cells the major end products were the disaposins, with A-B and C-D derived from the tetrasaposin, A-B-C-D, or with B-C and C-D derived from the trisaposin, B-C-D. In insect and mammalian cells, the nonsignal NH2-terminal peptide preceding saposin A (termed Nter) was usually removed prior to saposin A cleavage. In NT2-derived differentiated neurons, precursor tetrasaposins containing A-B-C-D were secreted with and without Nter. Immunofluorescence studies using prosaposin-specific antisera showed large steady state amounts of uncleaved prosaposin in Purkinje cells, cortical neurons, and other specific cell types in adult mice. These studies indicate that prosaposin processing is highly regulated at a proteolytic level to produce prosaposin, tetrasaposins, or mature monosaposins in specific mammalian cells.

Localization of NADPH diaphorase/nitric oxide synthase in the optic nerve of the normal guinea pig: a light and electron microscopic study

The aim of this study is to determine the presence and subcellular distribution of NADPH diaphorase (NADPH-d)/nitric oxide synthase (NOS) in the optic nerve of the normal guinea pig. Optic nerve specimens were stained by NADPH-d histochemistry, and double labeled by combining NADPH-d histochemistry with immunostaining for (a) anti-glial fibrillary acidic protein (GFAP) antibody for recognition of astrocytes, (b) griffonia simplicifilia B4-isolectin (GSA-IB4) horse radish peroxidase (HRP)-conjugate for identification of microglia, or (c) oligodendrocyte-associated antibodies to carbonic anhydrase isoenzyme II (CA-II) or to galactocerebroside (GalC) for visualization of oligodendrocytes. In addition, constitutive NOS (cNOS) and inducible NOS (iNOS) immunostaining were used for colocalization with NADPH-d histochemistry. Light microscopy revealed NADPH-d reaction product in the blood vessels and neuroglia of the unmyelinated optic nerve head and myelinated retrobulbar optic nerve. Double labeling with GFAP immunoperoxidase combined with NADPH-d histochemistry revealed both activities in astrocytes. Microglia were labeled with GSA-IB4 isolectin HRP-conjugate, but they did not have NADPH-d activity. Oligodendroglia were immunolabeled with anti CA-II or anti GalC antibodies, but they did not have NADPH-d activity. Both iNOS and cNOS immunoperoxidase labeled astrocytes, but not microglia or oligodendroglia. Under transmission electron microscopy, NADPH-d reaction product appeared as electron-dense particles. These particles were seen in the cytoplasm of endothelial cells, perivascular smooth muscle cells and fibrous astrocytes. Axons and myelin were devoid of NADPH-d activity. This study demonstrates the existence and cellular distribution of NADPH-d/NOS activity in endothelial cells, perivascular smooth muscle cells and fibrous astrocytes of the optic nerve of the normal guinea pig. The presence of these non-neuronal sources of NOS in the optic nerve provides the foundation for future comparative studies of the functional role of reactive oxygen induced toxicity in disorders affecting the optic nerve.

An acidic amino acid-specific protease from germinating soybeans

The degradation of the beta-conglycinin protein reserves in soybean seeds during germination and early growth begins with the proteolysis of its alpha and alpha' subunits by an enzyme called Protease C1. In the pathway, a number of proteolytic intermediates are produced and subsequently degraded. Determination of the N-terminal sequences of these intermediates provides insight regarding the requirements of the cleavage sites. The N-terminal sequence of three such proteolytic intermediates has been determined. The sequence has been located in the published sequences of the beta-conglycinin subunits. Comparing these cleavage sites, plus those of two others previously delineated, shows that the P1' and P4' positions always bear either a Glu or an Asp residue while the P1 position always bears either a Glu or a Gln residue. In addition, other sites from P3 to P7' are also rich in either Glu or Asp, and the whole region is predicted to be in a alpha-helix. Consistent with the observation, synthetic poly-L-Glu inhibits the Protease C1-catalysed degradation of the alpha and alpha' subunits of beta-conglycinin. Poly-L-Glu (av. M(r) = 1000) at 12.5 mM was more effective at inhibiting the reaction than poly-L-Glu (av. M(r) = 600) or poly-L-Glu (av. M(r) = 14,300) at the same concentration. Comparing large synthetic polypeptides at 12.5mM, inhibition by poly-L-Asp (av. M(r) = 15,000) is as effective as poly-L-Glu (av. M(r) = 14,300), while poly-L-Ser (av. M(r) = 15,000) had no effect at all. Poly-D-Glu (av. M(r) = 15,000) is a better inhibitor than poly-L-Glu of the same size. A serine protease of similar molecular weight as Protease C1 and also capable of catalysing the proteolysis of the alpha and alpha' subunits of beta-conglycinin to generate proteolytic intermediates of the same size has been found in mung bean.

Endocardial endothelium and myocardial performance in rats: effects of changing extracellular calcium and phenylephrine

It is known that endocardial endothelium (EE) modulates the performance of its subjacent myocardium. However, one species where these effects have been more difficult to describe is the rat. As the rat is a species which is used to evaluate the contractile effects of various pathologic conditions, a better appreciation of the contractile effects of EE and its modulatory role on the contractile effects of inotropic substances is important. In this study, the contractile effects of increasing extracellular calcium concentrations (0.7 mM to 3.25 mM) and phenylephrine (10(-7) to 10(-4) M) on rat papillary muscles with intact endocardial endothelium (EE on) and after endocardial endothelial removal (EE off) were assessed. At 0.7 mM extracellular calcium concentration, endocardial endothelial removal decreased all measured indices of myocardial performance (P < 0.05 EE on v EE off), except for maximum rate of unloaded muscle shortening (Vmax) which did not change, and decreased time to peak tension development (TTPT) as well as shortening of time to half tension decline from peak tension (RT1/2) shortening. Increasing extracellular calcium concentration from 0.7 mM to 3.25 mM caused all indices of myocardial performance and RT1/2 to increase more in muscles without EE, such that at 2.5 mM extracellular calcium all differences between EE on and EE off had disappeared. The only exception was TTPT which decreased with increasing extracellular calcium concentrations in muscles with EE on but increased in muscles with EE off. Again, at 2.5 mM extracellular calcium concentration differences in TTPT between EE on and EE off had disappeared. Except for minor differences on TTPT, increasing phenylephrine concentrations had similar contractile effects on muscles with EE on and EE off. These results indicate that EE modulates rat myocardial contraction and that these effects are best observed at lower extracellular calcium concentrations (0.7 mM). They also indicate that EE does not appear to significantly modulate the myocardial effects of alpha-adrenergic agonists in the rat.

Vascular-derived myocardial contractile factor: positive myocardial inotropic substance released from medial layer of the canine aorta

Interactions between the various cell types that make up the cardiovascular system are known to play an important role in maintaining homeostasis. One area about smooth muscle cells that has received little attention, despite the production of a wide variety of mediators by smooth muscle cells, is their effect on myocardial function. In this study, the myocardial contractile effects of four different types of dog aortic strips on rabbit papillary muscles were evaluated. Of these, medial vascular smooth muscle strips most consistently (65% of the time) produced a "vascular-derived contractile factor" (VDCF), which caused a 15% increase in isometric twitch tension and a 24% increase in isotonic twitch shortening with no change in twitch configuration. Endovascular strips with or without intact endothelium and complete aortic rings had less consistent effects. Vascular-derived contractile factor was stable after freezing at -80 degrees C, its activity was not modified by a broad spectrum peptidase, but it was heat-labile. The angiotensin II blocker, losartan, did not modify its effects. However, incubation with indomethacin did reduce, but did not eliminate, the contractile effects of vascular strips. The addition of alpha 1- and beta-blockers did not further modify the effects of VDCF. Endocardial endothelial removal increased the effects of VDCF. No correlation existed between endothelin levels and the contractile effects of vascular strips. It is concluded that VDCF is produced by the medial layer of large vessels but its exact cellular origin is uncertain. These findings expand the ever-increasing understanding of the inter-relationship between the structures that make up the cardiovascular system, and open the door to new studies evaluating the inter-relationship of vessels and myocardium.

Efficient catalysis by beta-lactamase from Staphylococcus aureus PC1 accompanied by accumulation of an acyl-enzyme

The pH- and temperature-dependence of steady-state kinetic parameters for 6-beta-(2-furyl)-acryloylamido-penicillanic acid showed it to be a good substrate of staphylococcal PC1 beta-lactamase, and the viscosity-dependence of K(m)/k(cat) indicated that steps up to the formation of the acyl-enzyme were partially diffusion-limited. In the pH range 4-9, a pre-steady-state transient blue shift in the UV absorption spectrum of the bound furyl-acryloylamido chromophore was of constant amplitude and decayed to the spectrum of the product with a first-order rate constant equal to k(cat). The spectrum of the isolated denatured acyl-enzyme was similar to that of the methyl ester of furyl-acryloylpenicilloic acid, pointing to non-covalent interactions with the folded protein, possibly associated with the charge on Glu-166, as the source of the blue-shifted spectrum. Taken together, these results point to a rapid acylation and slower deacylation at Ser-70 and imply that ionization of groups affecting enzyme activity at alkaline pH, for which likely candidates are Lys-73 and Lys-234, affect the rate of deacylation.

Functional organization of saposin C. Definition of the neurotrophic and acid beta-glucosidase activation regions

Saposin C is an essential co-factor for the hydrolysis of glucosylceramide by acid beta-glucosidase in mammals. In addition, prosaposin promotes neurite outgrowth in vitro via sequences in saposin C. The regional organization of these neurotrophic and activation properties of saposin C was elucidated using recombinant or chemically synthesized saposin Cs from various regions of the molecule. Unreduced and reduced proteins were analyzed by electrospray-mass spectrometry to establish the complement of disulfide bonds in selected saposin Cs. Using saposin B as a unreactive backbone, chimeric saposins containing various length segments of saposin B and C localized the neurotrophic and acid beta-glucosidase activation properties to the carboxyl- and NH2-terminal 50% of saposin C, respectively. The peptide spanning residues 22-31 had neurotrophic effects. Molecular modeling and site-directed mutagenesis localized the activation properties of saposin C to the region spanning residues 47-62. Secondary structure was needed for retention of this property. Single substitutions of R and S at the conserved cysteines at 47 or 78 diminished but did not obliterate the activation properties. These results indicate the segregation of neurotrophic and activation properties of saposin C to two different faces of the molecule and suggest a topographic sequestration of the activation region of prosaposin for protection of the cell from adverse hydrolytic activity of acid beta-glucosidase.

Solubilization and partial characterization of extensin fragments from cell walls of cotton suspension cultures. Evidence for a covalent cross-link between extensin and pectin

Extensin, a major hydroxyproline (Hyp)-rich glycoprotein in walls of cultured cells of dicotyledonous plants, is very difficult to solubilize. To learn about the nature of the insolubilization, we have tested the ability of a variety of selective hydrolytic methods, and combinations of them, to liberate extensin or fragments of extensin from suspension-culture cell walls. After the complete deglycosylation of cotton (Gossypium hirsutum L.) walls, trypsinization solubilized 80% of the Hyp. The sequences of three abundant peptides were: (a) serine-Hyp-Hyp-Hyp-Hyp-Hyp-Hyp-serine-Hyp-Hyp-lysine, (b) serine-Hyp-Hyp-Hyp-Hyp-valine-lysine, and (c) serine-Hyp-Hyp-serine-alanine-Hyp-lysine. After a sequential treatment of walls with endopolygalacturonase, cellulase, -73 degrees C anhydrous hydrogen fluoride solvolysis, and ammonium bicarbonate extraction, only sugars indicative of rhamnogalacturonan I and protein remained insoluble. Trypsin treatment of this residue liberated 50% of the Hyp. A significant proportion of rhamnogalacturonan-associated sugars co-solubilized and co-purified along with the extensin fragments following the trypsinization. By sodium dodecyl sulfate gel electrophoresis and gel filtration, the glycopeptides fell into two classes. One class contained distinctly sized molecules with relative molecular weights in the range of 4,000 to 24,000. The other class did not enter the resolving gel and was hetero-disperse. After complete deglycosylation by a 0 degrees C anhydrous hydrogen fluoride treatment, the first class was little affected in its electrophoretic mobility, whereas the larger heterogeneous material mostly entered the separating gel. After further trypsinization of the deglycosylated peptides and analysis by capillary zone electrophoresis, the peptides in both size classes were shown to contain the sequences described above. From our observations we suggest that cotton extensin becomes insolubilized into cell walls in part by pectin-protein cross-links in addition to the protein-protein (or protein-phenolic-protein) cross-links that have been repeatedly suggested.

Zero frequency masking and a model of contrast sensitivity

Stimulating the visual system tends to desensitize it to certain stimulus properties. Such desensitization is usually called adaptation or masking, but the distinction between the two is unclear. Nonspecific desensitization by light is usually regarded as adaptation, whereas pattern-specific desensitization is typically considered masking. Here we unify the treatment of such desensitizing phenomena by handling both in the spatial frequency domain. The amount of adapting light in a stimulus is represented in the spatial frequency domain by the component at zero frequency. To determine whether such adapting light acts like other components in the spatial frequency domain, we compared the effect of masking by the zero frequency component with the effects of masking by components at other frequencies. We show that the zero frequency component acts like other masking components, decreasing sensitivity to nearby test frequencies and thereby producing the insensitivity to low spatial frequencies that gives the contrast sensitivity curve its band-pass shape at high light levels. Treating light adaptation as masking by the zero frequency component leads to a general model that describes visual sensitivity to test gratings of varying spatial frequency at varying mean luminance, in the presence (or absence) of masking gratings of varying spatial frequency. Individual components of the model provide insight into visual processing at the system level.

Coupling of a signal response domain in I kappa B alpha to multiple pathways for NF-kappa B activation

The eukaryotic transcription factor NF-kappa B plays a central role in the induced expression of human immunodeficiency virus type 1 and in many aspects of the genetic program mediating normal T-cell activation and growth. The nuclear activity of NF-kappa B is tightly regulated from the cytoplasmic compartment by an inhibitory subunit called I kappa B alpha. This cytoplasmic inhibitor is rapidly phosphorylated and degraded in response to a diverse set of NF-kappa B-inducing agents, including T-cell mitogens, proinflammatory cytokines, and viral transactivators such as the Tax protein of human T-cell leukemia virus type 1. To explore these I kappa B alpha-dependent mechanisms for NF-kappa B induction, we identified novel mutants of I kappa B alpha that uncouple its inhibitory and signal-transducing functions in human T lymphocytes. Specifically, removal of the N-terminal 36 amino acids of I kappa B alpha failed to disrupt its ability to form latent complexes with NF-kappa B in the cytoplasm. However, this deletion mutation prevented the induced phosphorylation, degradative loss, and functional release of I kappa B alpha from NF-kappa B in Tax-expressing cells. Alanine substitutions introduced at two serine residues positioned within this N-terminal regulatory region of I kappa B alpha also yielded constitutive repressors that escaped from Tax-induced turnover and that potently inhibited immune activation pathways for NF-kappa B induction, including those initiated from antigen and cytokine receptors. In contrast, introduction of a phosphoserine mimetic at these sites rectified this functional defect, a finding consistent with a causal linkage between the phosphorylation status and proteolytic stability of this cytoplasmic inhibitor. Together, these in vivo studies define a critical signal response domain in I kappa B alpha that coordinately controls the biologic activities of I kappa B alpha and NF-kappa B in response to viral and immune stimuli.

Plasma membrane intrinsic proteins of Beta vulgaris L

The plasma membrane (PM) of higher plants contains numerous proteins; however, due to their low abundance, only a few have been identified and characterized by direct biochemical approaches. The major intrinsic protein (MIP) family is a class of highly hydrophobic integral membrane proteins thought to function as channels that facilitate the passage of water, small solutes, and possibly other moieties through the membrane. A family of PM intrinsic proteins was purified and characterized from PM vesicles derived from storage tissue of Beta vulgaris L. using the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate. This PM intrinsic protein-enriched fraction also contains high levels of UDP-glucose:(1,3)-beta-glucan (callose) synthase activity. Dithiothreitol is required to visualize the monomeric species of these highly hydrophobic integral membrane proteins. Sequence analysis of tryptic fragments derived from polypeptides of 31 and 27 kD revealed significant homologies to plant MIPs identified from cloned sequences. These MIPs include clone 7a from pea and RD28 from Arabidopsis, both of which are water-stress proteins, a tomato ripening-associated membrane protein, and PIP 2b, a PM-bound water channel protein from Arabidopsis. MIPs, therefore, represent abundantly occurring components of PMs derived from beet storage tissue.