Free radical reduction in the human epidermis

The human epidermis presents the first line of defense against invading free radicals. Therefore, the surface of the skin must be equipped to deal with both the penetration of ultra-violet light as well as the neutralization of reactive photochemical products such as superoxide anion radical, hydrogen peroxide and especially hydroxyl radicals. Consequently, the human epidermis contains a variety of anti-oxidants to reduce oxygen radicals and hydrogen peroxide. The photochemical production of hydroxyl radicals, from both extracellular and intracellular hydrogen peroxide, is of special significance to the integrity of cells in the human epidermis. Recently, both biochemical and clinical studies on the healthy human population, and on patients with pigmentation disorders, suggested a connection between free radical defense by plasma membrane associated thioredoxin reductase and melanin biosynthesis. This research provided the first evidence for a direct relationship between free radical concentration and pigmentation. Furthermore, this system has been shown to be regulated by both extracellular and intracellular calcium concentrations. Clinical studies show depigmentation disorders vitiligo and tyrosinase positive albinism (Hermansky-Pudlak syndrome) appear to have defective calcium uptake systems influencing both free radical defense and melanin biosynthesis.     

Do light/dark cycles of medium frequency enhance phytoplankton productivity?

It has been suggested that turbulence with the resultant light/dark cycle and light gradient through which phytoplankton move, enhances their productivity. The stationary bottle incubation technique for estimating rates of primary productivity has mainly been criticized because of bottle effects, the elimination of natural turbulence and the presence of photo-inhibition. In a series of experiments where productivity was measured over static profiles and compared to the productivity in a mixed system, no definite conclusion could be reached regarding the effect of varying light/dark cycles of medium frequency (seconds to minutes). It appeared as though the ratio of the euphotic depth to mixing depth (Z _eu/Z _m) influenced productivity more than the duration of the light/dark cycle. The static bottle incubation method gave higher integral productivities than the mixed samples at low ratio's ofZ _eu/Z _m. It is suggested that mixing has two separate, but synergistic effects i.e. it not only moves the phytoplankton cells through a light/dark cycle, but also decreases the boundary layer, which increases the rate of exchange through the cell wall of nutrients and metabolites. In doing so more nutrients are available and light could be utilized more efficiently and therefore, productivity is increased.     

Structure-Biological Activity Relationships in Alfalfa Antimycotic Saponins: The Relative Activity of Medicagenic Acid and Synthetic Derivatives Thereof Against Plant Pathogenic Fungi1

The antimycotic activity of medicagenic acid and of some synthetic derivatives thereof was tested against plant pathogenic fungi. In general they all possess antimycotic activity. Furthermore, in the case of Sclerotium rolfsii, compounds where the hydroxyl functions of the aglycon remained unchanged (medicagenic acid and its dimethyl ester) or could be enzymically released (3-0-β-D-glucoside of medicagenic acid dimethyl ester) were significantly more active than compounds where these functions were modified by acetylation or methylation. Selective 2-0-methylation of medicagenic acid and comparison of the antimycotic activity of the resulting derivative against S. rolfsii to that of other derivatives suggests that a potential free hydroxyl at position 3 is essential to antimycotic activity.     

Polarized distribution of binding sites for concanavalin A and wheat-germ agglutinin in the zona pellucida of goodeid oocytes (teleostei)

Summary Zonae pellucidae of the viviparous goodeid teleosts Girardinichthys viviparus, Xenoophorus captivus, and Xenotoca eiseni were investigated ultrastructurally, and binding sites for ConA and WGA were localized on cross-sections using a colloidal gold technique. In late stages of development, the oocytes are surrounded by a three-zonated acellular matrix multiply perforated by pore canals allowing long microvilli of the oocyte to penetrate interstices of the follicle epithelium. Together, the surface of the microvilli and zona pellucida is coated by a thin layer of homogeneous slightly electron-dense material. In early oogenesis, the thin acellular layer is entirely packed with binding sites for WGA, whereas those for ConA occur only sparsely. Three-zonated zonae pellucidae amply contain both WGA and ConA receptors. The asymmetric labelling pattern obtained with both lectin protein gold preparations indicates a polarized organization of the different glycoconjugates. WGA receptors are concentrated within the outer region of the zona pellucida. Labelling with ConA-HRP-Au complexes produced heavy deposits of marker beads within the inner two thirds of the zona pellucida and weak labelling of the superficial coat. After prolonged digestion with neuraminidase, WGA binding sites were no longer detectable.Supported by the Deutsche Forschungsgemeinschaft (Schi 268/1-1)     

Lectin histochemistry of brains from a murine mutant carrying a storage disorder

Summary A strain of Balb/c mice with neurovisceral storage disorder exhibits metabolic and phenotypic manifestations similar to those found in Niemann-Pick type C and D patients. The storage material in the brain reacted positively with periodate-Schiff reagent. To identify the chemical nature of the storage material we applied lectin histochemistry on paraffin-embedded and frozen sections, using biotinylated lectins and avidin-biotin-peroxidase complex. Major abnormalities were noted in the neurons and glia cells. Swollen neurons were stained heavily by Con A and S-WGA, whereas glia cells, mainly astrocytes, which were abundant both in the cerebrum and cerebellum, were positive to RCA-I, GS-I, PNA, S-WGA and WGA. The myelin tracts reacted with PNA, SBA and RCA-I but to a lesser extent in affected animals when compared to normals.Frozen brain sections stained positively only after extraction with chloroform methanol prior to the lectin treatment and revealed a lectin binding pattern similar to that of the paraffin-embedded preparations. The data presented here show that the stored glucoconjugates in the neurons are of a different chemical composition than those found in glia cells. Since only paraffin embedded sections or lipid extracted frozen sections reacted with the lectins, we suggest that the stored glucoconjugates are glycoproteins or oligosaccharides rather than glycolipids.     

Untreated asymptomatic bacteriuria in girls: II--Effect of phenoxymethylpenicillin and erythromycin given for intercurrent infections.

OBJECTIVE--To investigate the effects of phenoxymethylpenicillin and erythromycin on urinary isolates from patients with untreated asymptomatic bacteriuria. DESIGN--Retrospective study of subgroup of patients from cohort followed up till the end of 1986. SETTING--Outpatient clinic for children with urinary tract infections. PATIENTS--51 Girls aged under 15 with untreated asymptomatic bacteriuria. INTERVENTIONS--Before 1982 intercurrent infections (mostly tonsillitis or otitis) were treated with phenoxymethylpenicillin; after 1982 erythromycin treatment was preferred. END POINTS--Change of bacterial strain in urinary tract and symptomatic recurrences of disease. MEASUREMENTS AND MAIN RESULTS--Bacteria identified by serotype and electrophoretic type and compared before and after antibiotic treatment. Bacteriuria eradicated and replaced by new strains in most patients treated with phenoxymethylpenicillin, leading to symptomatic recurrences in about 15%. Conversely, patients given erythromycin rarely showed change in bacteriuria and none suffered symptomatic recurrence. CONCLUSIONS--In girls with untreated asymptomatic bacteriuria the use of phenoxymethylpenicillin for intercurrent infections may lead to a change of urinary bacteria and leave them at substantial risk of acute pyelonephritis. With erythromycin this risk is small (2/20 courses in this series).     

Untreated asymptomatic bacteriuria in girls: I--Stability of urinary isolates.

OBJECTIVE--To assess the frequency of spontaneous changes of bacterial strains in patients with untreated asymptomatic bacteriuria. DESIGN--Retrospective analysis of samples from all patients with renal scarring and random sample of patients with normal kidneys. SETTING--Outpatient clinic for children with urinary tract infections. PATIENTS--54 Girls aged 3.3-15.5 years with untreated asymptomatic bacteriuria caused by Escherichia coli. INTERVENTION--None. END POINT--Change in bacterial strain. MEASUREMENTS AND RESULTS--Serotyping and electrophoretic analysis of sequential bacterial isolates, representing 151 patient years of untreated asymptomatic bacteriuria. A total of 24 changes of strain were identified. Eleven were related to medical interference such as treatment of other infections with antibiotics. CONCLUSIONS--Spontaneous changes of strain were uncommon, one change in 11.6 patient years, and thus are not a characteristic feature of the course of asymptomatic bacteriuria.     

MHC class II invariant chains in antigen processing and presentation

Most protein antigens cannot elicit a T-cell response unless they are processed to peptides, which are then presented to T lymphocytes by surface MHC class II molecules. Recent evidence supports an essential role of the invariant chain associated with class II MHC polypeptides in antigen processing.     

A technique for normalizing centre of pressure paths

Centre of pressure paths may be expected to provide useful information in the analysis of gait. In this paper, a technique for normalizing and averaging centre of pressure paths is presented. It utilizes force data obtained from force platform measurements together with information about the placement of the foot on the force platform. This placement is described by specifying the location of the 'centre' and 'midline' of the foot which are defined for a footprint. The coordinate system associated with a footprint is defined and centre of pressure locations are determined in relation to this system. A comparison of the centre of pressure paths obtained using this method and the method proposed by Cavanagh [J. Biomechanics 11, 487-491 (1978)] shows significant differences. It is concluded that the selection of an appropriate technique to obtain centre of pressure paths is important.     

Binding properties of detergent-solubilized NCAM

An assay has been designed for the identification of NCAM-binding proteins present in an NP-40 detergent extract of brain membranes. This method, which is capable of analyzing both heterophilic and homophilic interactions, uses species-specific antibodies against NCAM in combination with radioiodination, so that after unlabeled chicken and iodinated frog brain membrane proteins were allowed to interact, the chicken NCAM could be specifically isolated by immunoaffinity adsorption. The radiolabeled frog proteins coisolated with chicken NCAM were then characterized by one- and two-dimensional gel electrophoresis in combination with immunoblotting. The only detectable NCAM-binding proteins were identified as the 140- and 180-kD forms of NCAM. The presence and absence of polysialic acid on NCAM did not change the amount or nature of the frog proteins immunopurified under these conditions. As an alternative for detecting heterophilic ligands, a simplified immunoprecipitation method was employed using either iodine or sulfate radiolabels. Again under these conditions only NCAM was detected. These results are consistent with the hypothesis that the major binding protein for NCAM is NCAM itself, and suggest that differences in polysialic acid content do not directly alter the properties of NCAM's homophilic binding site.