Stem surface injuries of 20 species of succulent Euphorbia (Euphorbiacae) from South Africa

Cactus and succulent Euphorbia plants have green stems that are exposed to sunlight over long periods. Previous research demonstrated that barking injuries occur to stem surfaces of 20 species of cacti in the Americas. For these 20 cactus species the amounts of injuries were related to annual amounts of sunlight exposure on surfaces. Cacti with many injuries had high mortality rates. Data herein show that stem surfaces of 20 species of Euphorbia in South Africa have identical surface injuries as for cacti. Euphorbia plants at 30°S show a mean ratio of scale and bark injuries of 3.5:1 of equatorial-facing to polar-facing surfaces, a ratio is similar to the 4:1 of annual sunlight exposure ratio at that latitude. Results show that Euphorbia stems have injuries on younger tissues than cactus species. Thus, Euphorbia stems are more sensitive than cactus stems. Euphorbia species with most stem injuries had smooth (non-undulate) surfaces, a one-celled epidermal cell layer only, cortex cells that abutted the epidermis, and initial injuries that involved only epidermal cells. This is the first report of identical stem surface injuries to Euphorbia species that are identical to surface injuries to cactus species worldwide. Moreover, the amounts on stem injuries on Euphorbia and long-lived, columnar cactus species are highly correlated with relative amounts of sunlight on stem surfaces over the annual cycle. These results suggest that these species are good bio-indicators of annual sunlight exposure.     

Seasonal and diurnal leaf orientation,bifacial sunlight incidence,and leaf structure in the sand dune herb Hydrocotyle bonariensis

A conceptual model has been proposed whereby leaf orientation and resulting sunlight exposure dictate functional leaf structure. Specifically, the model states that this relationship is driven by the absolute amount and ratio of incident sunlight on adaxial and abaxial leaf surfaces. To test this model, the relationships between corresponding values of leaf orientation and incident sunlight on both leaf surfaces were measured for the sand dune herb Hydrocotyle bonariensis over a growth season, along with examination of leaf structure. For mature leaves, leaf angle from horizontal and azimuth angle significantly increased over the growing season, indicating diurnal midday avoidance and seasonal maximization of incident sunlight. Consequently, seasonal changes in leaf orientation resulted in an overall decrease in midday sunlight incidence on the adaxial surface and a slight shift in the daily occurrence of peak abaxial incidence. Adaxial surfaces received three to four times more sunlight than abaxial surfaces, and leaf cross-sections revealed relatively thick (564 μm) leaves with multiple adaxial palisade layers and stomata on both leaf surfaces, as predicted by the conceptual model and measured ratio of incident sunlight on adaxial and abaxial leaf surfaces. These data provide further evidence of the relationship between leaf orientation and resulting absolute levels of sunlight incidence on both leaf surfaces, as well as their ratio, and corresponding differences in internal and external leaf structure.     

Effect of sunlight on the survival of Salmonella on surfaces

AIMS: To investigate the effect of simulated full-spectrum tropical sunlight on the survival of Salmonella in droplets on surfaces. MATERIALS AND RESULTS: The survival on surfaces of three Zambian strains of Salmonella enterica serovars Enteritidis and Heidelberg was compared with that of a strain of S. enterica serovar Enteritidis phage type (PT) 4 with known characteristics which had been isolated from poultry in the UK. Samples were taken from surfaces every hour for 3 h and after 24 h exposure in either dark or 12 h light/12 h dark cycle conditions. Differences were analysed for significance using a one-way analysis of variance (anova). Results show that there were a significantly higher number of cells surviving on surfaces after 24 h in the dark when compared with populations exposed to a 12 h light/12 h dark cycle. Significantly more cells also survived exposure to sunlight under dirty than clean conditions. CONCLUSIONS: Exposure to sunlight results in a significant decrease in numbers of Salmonella on surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: Under field conditions exposure of contaminated surfaces to sunlight could be used in place of chemical methods of control as a cheaper way to reduce Salmonella contamination of surfaces.     

Associations between leaf structure, orientation, and sunlight exposure in five Western Australian communities

Five plant communities in Western Australia, as well as selected desert and Rocky Mountain species of the western USA, were surveyed to evaluate associations among leaf structure, orientational properties, and the sunlight exposure and precipitation characteristic of each community. Selected leaf structural features have been associated previously with photosynthetic function and included shape, thickness, the ratio of thickness to width, stomatal distribution, leaf surface coloration, and the number and distribution of palisade cell layers. Decreases in annual precipitation (<4 to over 15 cm/yr) and increases in total daily sunlight (4.2 to 29.2 mol photons/m1) corresponded strongly to an increase in the percentage of species in a given community with more inclined (more inclined than +/- 45 degrees from horizontal) or thicker leaf mesophyll (>0.4 mm) leaves. Also, the percentage of species with a leaf thickness to width ratio >0.1, which were amphistomatous, or which had palisade cell layers beneath both leaf surfaces, increased from >20% in the highest rainfall and lowest sunlight community to >80% in the community with least rainfall but greatest sunlight exposure. Over 70% of the species in the most mesic, shaded community had lighter abaxial than adaxial leaf surfaces (leaf bicoloration). All of the above structural features were positively associated with a more inclined leaf orientation (r1 = 0.79), except for leaf bicoloration, which was negatively associated (r1 = 0.75). The ratio of adaxial to abaxial light was more strongly associated with leaf bicoloration (r1 = 0.83) and the presence of multiple adaxial and isobilateral palisade cell layers(r1 = 0.80) than with total incident sunlight on just the adaxial leaf surface (r1 = 0.69 and 0.73, respectively). These results provide field evidence that leaf orientation and structure may have evolved in concert to produce a photosynthetic symmetry in leaf structure in response to the amount of sunlight and other limiting factors of the community. This structural symmetry may serve fundamentally to regulate the distribution of both light and CO2 levels inside the leaf and, thus, increase photosynthetic CO2 uptake per unit leaf biomass.     

In vivo activation of human immunodeficiency virus type 1 long terminal repeat by UV type A (UV-A) light plus psoralen and UV-B light in the skin of transgenic mice.

UV irradiation has been shown to activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in cell culture; however, only limited studies have been described in vivo. UV light has been categorized as UV-A (400 to 315 nm), -B (315 to 280 nm), or -C (less than 280 nm); the longer wavelengths are less harmful but more penetrative. Highly penetrative UV-A radiation constitutes the vast majority of UV sunlight reaching the earth's surface but is normally harmless. UV-B irradiation is more harmful but less prevalent than UV-A. In this report, the HIV-1 LTR-luciferase gene in the skin of transgenic mice was markedly activated when exposed to UV-B irradiation. The LTR in the skin of transgenic mice pretreated topically with a photosensitizing agent (psoralen) was also activated to similar levels when exposed to UV-A light. A 2-h exposure to sunlight activated the LTR in skin treated with psoralen, whereas the LTR in skin not treated with psoralen was activated after 7 h of sunlight exposure. The HIV-1 LTR-beta-galactosidase reporter gene was preferentially activated by UV-B irradiation in a small population of epidermal cells. The transgenic mouse models carrying HIV-1 LTR-luciferase and LTR-beta-galactosidase reporter genes have been used to demonstrate the in vivo UV-induced activation of the LTR and might be used to evaluate other environmental factors or pharmacologic substances that might potentially activate the HIV-1 LTR in vivo.     

A surface modification strategy on silicon nitride for developing biosensors

A surface modification strategy for the use of giant magnetoresistive materials in the detection of protein-protein interactions is developed. This modification strategy is based on silanization of semiconductive materials. A native silicon nitride surface was treated with concentrated hydrofluoric acid to improve surface homogeneity. Nano-strip was used to oxidize silicon nitride to form a hydrophilic layer. Aminopropyltriethoxysilane was subsequently used to functionalize the treated surfaces to form amine groups, which were further activated with glutaraldehyde to introduce a layer of aldehyde groups. The effectiveness of this modification strategy was validated by chemiluminescence immunoassays of purified 6x His-HrpW of Pseudomonas syringae pv. tomato DC3000 and human transferrin. Signals with intensities related to concentrations of these two immobilized model proteins were observed. The modified surface was also validated by a more complex system: intercellular proteins secreted by DC3000. HrpW in these protein mixtures was successfully recognized by anti-HrpW antibodies when mixed proteins were immobilized onto activated surfaces. This surface modification strategy provides a platform onto which proteins can be directly immobilized for biosensor and protein array applications.     

Immobilization by Adsorption of Hydrophobic Lipase Derivatives to Porous Polymer Beads for Use in Ester Synthesis

A novel procedure for attaching lipase to certain kinds of hydrophobic surfaces is described. The procedure involves covalent derivatization of the protein molecule by reaction in solution with a hydrophobic imidoester, aldehyde or activated polyethylene glycol. The resulting protein derivative is then allowed to adsorb onto an insoluble hydrophobic surface. Quantitative adsorption is observed and the enzyme is bound very strongly on the support The number and nature of the hydrophobic substituents introduced in the chemical derivatization step can be easily controlled. The adsorption step occurs spontaneously upon exposure of the modified protein to a variety of hydrophobic materials. The hydrophobic lipase derivative obtained by reaction with PEG activated with p-nirrophenyl chloroformate, for example, adsorbs readily onto polyacrylate and polystyrene beads, with most of its esterification activity in organic solvent intact. Its thermostability is also greatly enhanced. Derivatization of lipase with hydrophobic groups greatly enhances its esterification activity in organic solvent, and its immobilization in this manner enables the preparation of a highly reactive biocatalyst for biotechnological application.     

Characterization of glucose oxidase immobilization onto mica carrier by atomic force microscopy and kinetic studies

Glucose oxidase (E.C 1.1.3.4) immobilized onto activated surface of mica was analyzed by enzymatic kinetics and visualization with atomic force microscopy (AFM). The activity of the immobilized enzyme decreased with the decrease of concentration of gamma-aminopropyltrimethoxysilane used for the first step of activation of mica, while AFM analysis showed similar homogeneous filling of the surface with the enzyme. The comparison of enzyme activity with its surface filling revealed that there has to be additional vertical structures, which cannot be visualized by the methods of AFM. The simultaneous decrease of the silanizing agent and the concentration of the enzyme led to molecular resolution for the enzyme on the surface of mica. This allows to propose the described method also for analyzing other surfaces of solid materials with coupled biomolecules.     

Ion beam treatment of titanium surfaces for enhancing deposition of hydroxyapatite from solution

Surface coating with hydroxyapatite (HA) is a common way to improve the osseointegration of orthopaedic and dental titanium (Ti)-based materials. The main problems with current techniques are changes in composition during heating and poor adhesion to the surface. An alternative method is deposition of HA onto an activated surface out of a solution. The present work studies the surface treatment involving ion implantation of Na into Ti to induce a modification in chemistry and morphology, showing sodium titanate (Na(2)TiO(3)) incorporated within the surface layer with concentration, depth distribution, and morphology depending on the parameters of the ion implantation. Such ion-implanted Ti surfaces actively induce heterogeneous precipitation of HA from a simulated body fluid containing physiological concentrations of calcium and phosphate ions. This is compared with the activation by NaOH etching. The growth of bone forming cells on the pure Na implanted surface is oriented without an increased bone formation. Cell growth on the NaOH etched surface is reduced. After deposition of HA on both surfaces cell the growth pattern was improved.     

Diazo coupling method for covalent attachment of proteins to solid substrates

We describe a process for covalently linking proteins to glass microscope slides and microbeads in a manner that optimizes the reactivity of the immobilized proteins and that is suitable for high-throughput microarray and flow cytometry analysis. The method involves the diazo coupling of proteins onto activated self-assembled monolayers formed from p-aminophenyl trimethoxysilane. Proteins immobilized by this method maintained bioactivity and produced enhanced levels of protein-protein interaction, low background fluorescence, and high selectivity. The binding of immobilized proteins to their specific binding partner was analyzed quantitatively and successfully correlated with solution concentrations. Diazotized surfaces bound more efficiently to proteins containing a hexahistidine tag than those without a his-tag. Moreover, significantly higher reactivity of the immobilized his-tagged proteins was observed on diazotized surfaces than on amine-terminated surfaces. Results suggest that his-tagged proteins are immobilized by reaction of the his-tag with the diazotized surface, thus offering the possibility for preferential orientation of covalently bound proteins.     

Immobilization chemistries suitable for use in the BIAcore surface plasmon resonance detector.

Surface plasmon resonance detectors, such as the BIAcore instrument produced by Pharmacia, show promise for the detection and quantitation of macromolecular interactions in a label-free mode. Such detectors rely on the covalent immobilization of one of the interacting species onto the sensing surface. To date, the only published chemistry for this purpose is reaction of primary amino-containing ligands with an N-hydroxysuccinimide (NHS) ester-activated surface. In an effort to increase the versatility of the BIAcore with respect to immobilizing ligands, we undertook an investigation of activation chemistries compatible with this system. Using readily available reagents, we demonstrated that the carboxylated dextran-coated sensing surface could be easily converted to functions other than NHS-esters, including amine-activated, hydrazine-activated, and sulfhydryl-activated surfaces. In addition, use was made of the streptavidin/biotin interaction to probe chemical modifications of the sensing surface, by employing specifically modified biotin derivatives.     

Delayed and sustained activation of extracellular signal-regulated kinase in human keratinocytes by UVA: implications in carcinogenesis

Exposure to the sun's UV radiation appears to be the most important environmental factor involved in the development of skin cancer. UVA is the major portion of UV radiation in sunlight and is considered to be a human carcinogen. In this study, we have investigated the delayed and sustained activation of ERK MAPK by UVA exposure. In parallel, a delayed Ras activation with a similar time course was observed after UVA exposure. The activated Ras was found to be localized in endomembranes such as the Golgi apparatus instead of plasma membranes. Expression of dominant negative Ras (N17Ras) abolished ERK activation by UVA. The presence of AG1478, an epidermal growth factor (EGF) receptor (EGFR) kinase inhibitor, had no effect on ERK or Ras activation, indicating that EGFR kinase activity is not involved in ERK activation by UVA. In contrast, protein kinase C (PKC) depletion by chronic 12-O-tetradecanoylphorbol-13-acetate treatment nearly abolished UVA-induced ERK and Ras activation. The presence of the Ca(2+)-dependent-PKC inhibitor Go6976 had a similar effect. These findings suggest that ERK activation by UVA is mediated by PKC in a Ras-dependent pathway. In addition, a gradual increase in intracellular calcium level after UVA exposure was detected by flow cytometry. The presence of the PLC inhibitor U73122 or the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N, N',N'-tetraacetic acid tetrakis (acetoxymethyl ester) (BAPTA-AM) blocked both ERK and Ras activation, suggesting that both PLC and calcium are required for ERK activation. Our findings demonstrated that, different from UVC and UVB, UVA-induced delayed and sustained ERK activation is EGFR kinase activity-independent, but PLC/calcium/PKC-mediated. The delayed and sustained ERK activation provides a survival signal to human HaCaT keratinocytes, which may serve as an important mechanism for cell transformation and potential skin carcinogenesis in vivo caused by UVA exposure.     

Physical proximity and functional association of glycoprotein 1balpha and protein-disulfide isomerase on the platelet plasma membrane

Platelet function is influenced by the platelet thiol-disulfide balance. Platelet activation resulted in 440% increase in surface protein thiol groups. Two proteins that presented free thiol(s) on the activated platelet surface were protein-disulfide isomerase (PDI) and glycoprotein 1balpha (GP1balpha). PDI contains two active site dithiols/disulfides. The active sites of 26% of the PDI on resting platelets was in the dithiol form, compared with 81% in the dithiol form on activated platelets. Similarly, GP1balpha presented one or more free thiols on the activated platelet surface but not on resting platelets. Anti-PDI antibodies increased the dissociation constant for binding of vWF to platelets by approximately 50% and PDI and GP1balpha were sufficiently close on the platelet surface to allow fluorescence resonance energy transfer between chromophores attached to PDI and GP1balpha. Incubation of resting platelets with anti-PDI antibodies followed by activation with thrombin enhanced labeling and binding of monoclonal antibodies to the N-terminal region of GP1balpha on the activated platelet surface. These observations indicated that platelet activation triggered reduction of the active site disulfides of PDI and a conformational change in GP1balpha that resulted in exposure of a free thiol(s).     

Attenuation of incident light in Galax urceolata (Diapensiaceae): concerted influence of adaxial and abaxial anthocyanic layers on photoprotection

Although anthocyanin coloration in lower (abaxial) leaf cells has been documented for numerous species, the functional significance of this character has not been comprehensively investigated according to habitat or leaf orientation. Here, we demonstrate that abaxial anthocyanin may function as a photoprotectant, similarly to its purported role in upper (adaxial) cells, in leaves vulnerable to high irradiance incident on abaxial surfaces. Spectral scans were derived for Galax urceolata leaves with the following phenotypes: abaxial or adaxial anthocyanin only, abaxial and adaxial anthocyanin, and no anthocyanin. To determine whether anthocyanins conferred protection from photoinhibition, maximum photosystem II efficiencies of red (anthocyanic) and green (acyanic) surfaces were compared during and after exposure to photoinhibitory conditions. Leaves were either positioned with their adaxial surfaces facing the light source or inverted to expose abaxial surfaces. Spectral scans showed increased absorptance of 500-600 nm wavelengths by red surfaces (consistent with the absorbance spectrum of anthocyanin), regardless of whether that surface was abaxial or adaxial. Leaves with anthocyanin in either illuminated surface were also photoinhibited less than leaves lacking anthocyanin in that surface. These results suggest that anthocyanic layers reduce absorbed sunlight in the mesophyll not only for adaxial surfaces, but also for the abaxial. Adaxial/abaxial anthocyanin plasticity may therefore be adaptive in high-light environments or during light-sensitive developmental stages where leaf orientation and/or substrate albedo are variable.     

Increase in sialic acids removable by neuraminidase during the shape change of platelets.

Human or rabbit platelets were activated by ADP or 5-hydroxytrypatamine and rapidly fixed with glutaraldehyde. The shape change associated with activation gave rise to an increase in sialic acids removable by neuraminidase. This increase, like the shape change, was prevented by adenosine or methysergide added before ADP or 5-hydroxytryptamine respectively. The results indicate the exposure of additional glycoprotein(s) on the platelet surface.     

Thermogenic and psychogenic recruitment of human eccrine sweat glands: Variations between glabrous and non-glabrous skin surfaces

Human eccrine sweat-gland recruitment and secretion rates were investigated from the glabrous (volar) and non-glabrous hand surfaces during psychogenic (mental arithmetic) and thermogenic stimuli (mild hyperthermia). It was hypothesised that these treatments would activate glands from both skin surfaces, with the non-thermal stimulus increasing secretion rates primarily by recruiting more sweat glands. Ten healthy men participated in two seated, resting trials in temperate conditions (25–26 °C). Trials commenced under normothermic conditions during which the first psychogenic stress was applied. That was followed by passive heating (0.5 °C mean body temperature elevation) and thermal clamping, with a second cognitive challenge then applied. Sudomotor activity was evaluated from both hands, with colourimetry used to identify activated sweat glands, skin conductance to determine the onset of precursor sweating and ventilated sweat capsules to measure rates of discharged sweating. From glandular activation and sweat rate data, sweat-gland outputs were derived. These psychogenic and thermogenic stimuli activated sweat glands from both the glabrous and non-glabrous skin surfaces, with the former dominating at the glabrous skin and the latter at the non-glabrous surface. Indeed, those stimuli individually accounted for ~90% of the site-specific maximal number of activated sweat glands observed when both stimuli were simultaneously applied. During the normothermic psychological stimulation, sweating from the glabrous surface was elevated via a 185% increase in the number of activated glands within the first 60 s. The hypothetical mechanism for this response may involve the serial activation of additional eccrine sweat glands during the progressive evolution of psychogenic sweating.     

Characterization of surface-immobilized layers of intact liposomes

Surface-immobilized liposome layers are of interest for various potential applications such as localized drug delivery, but their characterization is challenging. We have employed an AFM method and fluorescent dye release to analyze anchored liposomes. In addition, we studied whether the liposomes are surface-bound solely via specific interaction (NeutrAvidin/biotin) or whether physisorptive binding also plays a role. Liposomes containing PEG-biotin lipids were affinity bound to NeutrAvidin molecules which had been immobilized onto solid supports via three different hydrogel interlayers. After liposome docking, approaching the surface with a colloid probe mounted onto an AFM cantilever showed considerable compression behavior, consistent with expectation based on intact, deformable liposomes but not lipid bilayers, thus showing that disruption of liposomes did not occur upon immobilization onto these support surfaces. Plastic deformation suggestive of liposome disruption on compression was not observed. The kinetics of fluorescent dye release also demonstrated that intact liposomes had been successfully immobilized onto all three supports. Blocking surface-immobilized NeutrAvidin molecules with excess biotin in solution before exposure to liposomes showed that the docking of liposomes was dependent largely but not exclusively on biotin-NeutrAvidin affinity binding, with evidence for some nonspecific physisorption, as the extent of liposome binding onto blocked NeutrAvidin surfaces was appreciably lower than for unblocked surfaces but not zero. Finally, consecutive addition of further NeutrAvidin and liposome layers enabled fabrication of multilayers, and this was clearly seen in AFM compressibility and fluorescent dye release measurements.     

Fertilization Induces a Transient Exposure of Phosphatidylserine in Mouse Eggs

Phosphatidylserine (PS) is normally localized to the inner leaflet of the plasma membrane and the requirement of PS translocation to the outer leaflet in cellular processes other than apoptosis has been demonstrated recently. In this work we investigated the occurrence of PS mobilization in mouse eggs, which express flippase Atp8a1 and scramblases Plscr1 and 3, as determined by RT-PCR; these enzyme are responsible for PS distribution in cell membranes. We find a dramatic increase in binding of flouresceinated-Annexin-V, which specifically binds to PS, following fertilization or parthenogenetic activation induced by SrCl₂ treatment. This increase was not observed when eggs were first treated with BAPTA-AM, indicating that an increase in intracellular Ca²⁺ concentration was required for PS exposure. Fluorescence was observed over the entire egg surface with the exception of the regions overlying the meiotic spindle and sperm entry site. PS exposure was also observed in activated eggs obtained from CaMKIIγ null females, which are unable to exit metaphase II arrest despite displaying Ca²⁺ spikes. In contrast, PS exposure was not observed in TPEN-activated eggs, which exit metaphase II arrest in the absence of Ca²⁺ release. PS exposure was also observed when eggs were activated with ethanol but not with a Ca²⁺ ionophore, suggesting that the Ca²⁺ source and concentration are relevant for PS exposure. Last, treatment with cytochalasin D, which disrupts microfilaments, or jasplakinolide, which stabilizes microfilaments, prior to egg activation showed that PS externalization is an actin-dependent process. Thus, the Ca²⁺ rise during egg activation results in a transient exposure of PS in fertilized eggs that is not associated with apoptosis.     

UV hazard on a summer’s day under Mediterranean conditions, and the protective role of a beach umbrella

Mediterranean beaches are very crowded during summer and, because of the high values of solar UV radiation, the potential risk for human health is relevant. In this study, all-day measurements of biologically effective global and diffuse UV radiation for skin (UVBE_eryt) and eye (UVBE_pker, UVBE_pconj, UVBE_cat) disorders were carried out on differently tilted surfaces on a summers day on a Mediterranean beach. The role played by beach umbrellas in protection from excessive sun exposure was also investigated. Erythema, photokeratitis and cataract seem to require almost the same exposure time to reach the risk threshold dose. Under full sunlight, the highest global and diffuse UV values are reached on surfaces normally oriented towards sunlight and on horizontal surfaces, respectively. Over vertical surfaces, at this northern hemisphere site, global and diffuse UV radiation reaches maxima values in the south-facing direction around noon, while maxima values are reached early in the morning and late in the afternoon over surfaces facing east and west, respectively. The quality of the beach umbrellas protection (efficiency in blocking solar UV radiation) varies with surface orientation; the highest efficiency for our specific site and geometrical conditions occurs over horizontal surfaces, with efficiency being least over vertical surfaces when incident radiation values are still relevant.     

Protein adsorption at polymer-grafted surfaces: comparison between a mixture of saliva proteins and some well-defined model proteins

Grafting a dense layer of soluble polymers onto a surface is a well-established method for controlling protein adsorption. In the present study, polyethylene oxide (PEO) layers of three different grafting densities were prepared, i.e. 10-15 nm2, 5.5 nm2 and 4 nm2 per polymer chain, respectively. The adsorption of different proteins on the PEO grafted surfaces was measured in real time by reflectometry. Furthermore, the change of the zeta-potential of such surfaces resulting from adsorption of the proteins was determined using the streaming potential method. Both the protein adsorption and the zeta-potential were monitored for 1 h after exposure of the protein solution to the surface. The adsorption pattern for a mixture of saliva proteins was compared to those observed for a number of well-defined model-proteins (lysozyme, human serum albumin, beta-lactoglobulin and ovalbumin). The results of the adsorption kinetics and streaming potential measurements indicate that the effect of the PEO layer on protein adsorption primarily depends on the size and the charge of the protein molecules. The saliva proteins are strongly blocked for adsorption, whereas the change in the zeta-potential is larger than for the other proteins (except lysozyme). It is concluded that positively charged protein molecules, having dimensions larger than those of lysozyme, are involved in the initial stage of adsorption from saliva onto a negatively charged surface.