Chronic Inflammation, Oxidative Stress and Metabolic Plasticity: Three Players Driving the Pro-Tumorigenic Microenvironment in Malignant Mesothelioma

Malignant pleural mesothelioma (MPM) is a lethal and rare cancer, even if its incidence has continuously increased all over the world. Asbestos exposure leads to the development of mesothelioma through multiple mechanisms, including chronic inflammation, oxidative stress with reactive oxygen species (ROS) generation, and persistent aberrant signaling. Together, these processes, over the years, force normal mesothelial cells' transformation. Chronic inflammation supported by "frustrated" macrophages exposed to asbestos fibers is also boosted by the release of pro-inflammatory cytokines, chemokines, growth factors, damage-associated molecular proteins (DAMPs), and the generation of ROS. In addition, the hypoxic microenvironment influences MPM and immune cells' features, leading to a significant rewiring of metabolism and phenotypic plasticity, thereby supporting tumor aggressiveness and modulating infiltrating immune cell responses. This review provides an overview of the complex tumor-host interactions within the MPM tumor microenvironment at different levels, i.e., soluble factors, metabolic crosstalk, and oxidative stress, and explains how these players supporting tumor transformation and progression may become potential and novel therapeutic targets in MPM.

Protein Mass Fingerprinting and Antioxidant Power of Hemp Seeds in Relation to Plant Cultivar and Environment

Cannabis sativa (hemp) seeds are considered a functional food for their favorable contents of essential fatty acids, proteins and antioxidants. Beyond phenolics and carotenoids, the bioactivity of proteins has recently been investigated. However, plant genotype and environmental conditions can affect quantity and quality of macronutrients and phytochemicals in seeds, influencing their nutraceutical properties. In this study, the effects of plant variety and seed origin on the protein profile and antioxidant activity of hemp seeds were evaluated. Seeds from two cultivars, Secuieni Jubileu and Finola, were harvested from a mountain field located in Italy and compared with reference seeds used for sowing. Albumin and globulin extracts were obtained using the Osborne method and their antioxidant power was assayed (DPPH and ABTS methods). A matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry method was developed for protein fingerprinting analysis. Albumins from seeds of the mountain site showed higher radical scavenging activity and compounds of lower molecular weight than reference seeds, suggesting a role of proteins in the observed bioactivity. The MALDI-TOF method discriminated samples according to origin and variety, highlighting changes in the protein profile and identifying signals which could be used as markers of hemp cultivars.

The Immunological Role of Milk Fat Globule Membrane

Human milk is the ideal food for newborns until the age of six months. Human milk can be defined as a dynamic living tissue, containing immunological molecules, such as immunoglobulins, supra-molecular structures, such as the milk fat globule membrane (MFGM), and even entire cells, such as the milk microbiota. The milk composition changes throughout lactation to fulfill the infant’s requirements and reflect the healthy/disease status of the lactating mother. Many bioactive milk components are either soluble or bound to the MFGM. In this work, we focus on the peculiar role of the MFGM components, from their structural organization in fat globules to their route into the gastrointestinal tract. Immunometabolic differences between human and bovine MFGM components are reported and the advantages of supplementing infant formula with the MFGM are highlighted.

Study protocol on the safety and feasibility of a normocaloric ketogenic diet in people with amyotrophic lateral sclerosis

OBJECTIVES

This study evaluates the safety and feasibility of a normocaloric ketogenic diet (KD) in people with amyotrophic lateral sclerosis (ALS) for reducing hyperexcitability levels and modulating neuroinflammation.

METHODS

This is a prospective, open-label pilot study involving men and women diagnosed with ALS, ages 18 to 75 y. The primary outcome is the safety and reproducibility of the KD in people with ALS. We will monitor secondary clinical outcomes with the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale score, forced vital capacity, the Amyotrophic Lateral Sclerosis Assessment Questionnaire, blood parameters, and gut microbiota analyses. All participants will follow the KD for 8 wk. During the diet, the clinical status of all participants will be monitored every 15 d through neurologic and nutritional visits and biochemical markers. The research ethics committee approved the study.

RESULTS

Safety will be assessed by measuring the number and severity of adverse events, including death, and any changes in blood chemistry, vital signs, and clinical exam results. Tolerability will be assessed to complete the proposed 8 wk of treatment while maintaining adequate nutritional status without inducing malnutrition.

CONCLUSIONS

Adequate caloric intake is essential in ALS, because insufficient intake induces loss of body mass. We hope that the proposed study will provide a positive result in terms of the safety and feasibility of a KD in people ALS, with the purpose of developing a patient-centered diet program to limit disease progression and possibly improve survival.

Phytochemical and Ecological Analysis of Two Varieties of Hemp (Cannabis sativa L.) Grown in a Mountain Environment of Italian Alps

Hemp (Cannabis sativa L.) is a multifunctional crop that is capable of prompt environmental adaptation. In this study, a monoecious cultivar (Futura 75) and a dioecious one (Finola) were tested in a mountain area in Valsaviore (Rhaetian Alps, Italy; elevation: 1,100 m a.s.l.) during the growing season 2018. Phytochemical behavior was evaluated by different analytical approaches: HPLC-high-resolution mass spectrometry, SDS-PAGE LC-MS/MS, HS-SPME GC-MS, and GC-FID in order to obtain complete profile of two varieties cultivated in altitude. CSR functional strategy used for ecological evaluation revealed that both genotypes are mainly competitors, although Finola is more stress tolerator (C:S:R = 57:26:17%) than Futura (C:S:R = 69:15:16%). The Finola inflorescences were characterized by higher quantities of β-ocimene and α-terpinolene, while α- and ß-pinene accompanied by extremely high ß-myrcene were found as predominant in Futura. Both varieties were rich in sesquiterpenes (45 recognized) among which trans-caryophyllene and α-humulene were the most abundant. Total tetrahydrocannabinol level was lower than 0.1%, while the most abundant cannabinoid was cannabidiolic acid (CBDA): 2.3% found in Finola vs. 2.7% revealed for Futura. The level of corresponding neutral form, cannabidiol, varied drastically: 0.27% (Finola) vs. 0.056% (Futura). Finola showed the unique cannabinoid profile with unexpectedly high cannabidivarin, 2-fold higher that corresponding acidic analogue, whereas the particularity of Futura 75 was the occurrence of cannabigerolic acid (CBGA) in the quantities that was double than those exposed for Finola. The seeds from both chemovars proved to be rich in polyunsaturated fatty acids, and Finola showed a higher ratio ω6/ω3. No difference was found in the protein content, and the SDS-PAGE profile was similar. The most abundant protein was edestin, followed by heat shock protein 70, ß-conglycinin, and vicilin. In conclusion, comprehensive phytochemical and ecological study of two fiber-type varieties cultivated in Italian Alps displayed specific, legal, and safe cannabinoids profile, followed by particular terpene composition, polyunsaturated fatty acids content, and favorable protein profile. This postulates that geographical provenience of hemp should be considered in selecting a variety that would be suitable for a specific end-use nutraceutical application.

Cellulomonas fimi secretomes: In vivo and in silico approaches for the lignocellulose bioconversion

Lignocellulose degradation is a challenging step for value added products and biofuels production. Cellulomonas fimi secretes complex mixtures of carbohydrate active enzymes (CAZymes) which synergistically degrade cellulose and hemicelluloses. Their characterization may provide new insights for enzymatic cocktails implementation. Bioinformatic analysis highlighted 1127 secreted proteins, constituting the in silico secretome, graphically represented in a 2DE map. According to Blast2GO functional annotation, many of these are involved in carbohydrates metabolism. In vivo secretomes were obtained, growing C. fimi on glucose, CMC or wheat straw for 24 h. Zymography revealed degradative activity on carbohydrates and proteomic analysis identified some CAZymes, only in secretomes obtained with CMC and wheat straw. An interaction between cellobiohydrolases is proposed as a strategy adopted by soluble multimodular cellulases. Such approach can be crucial for a better characterization and industrial exploitation of the synergism among C. fimi enzymes.

SIRT1 at the crossroads of AKT1 and ERβ in malignant pleural mesothelioma cells

In this report, we show that malignant pleural mesothelioma (MPM) patients whose tumors express high levels of AKT1 exhibit a significantly worse prognosis, whereas no significant correlation with AKT3 expression is observed. We provide data that establish a phosphorylation independent role of AKT1 in affecting MPM cell shape and anchorage independent cell growth in vitro and highlight the AKT1 isoform-specific nature of these effects.

We describe that AKT1 activity is inhibited by the loss of SIRT1-mediated deacetylation and identify, by mass spectrometry, 11 unique proteins that interact with acetylated AKT1.

Our data demonstrate a role of the AKT1/SIRT1/FOXM1 axis in the expression of the tumor suppressor ERβ. We further demonstrate an inhibitory feedback loop by ERβ, activated by the selective agonist KB9520, on this axis both in vitro and in vivo.

Our data broaden the current knowledge of ERβ and AKT isoform-specific functions that could be valuable in the design of novel and effective therapeutic strategies for MPM.

Arbuscular mycorrhizal symbiosis affects the grain proteome of Zea mays: a field study

Maize is one of the most important crops worldwide and is strongly dependent on arbuscular mycorrhiza (AM) fungi, organisms that form a mutualistic association with land plants. In maize, AM symbiosis enhances spike dry weight, spike length, spike circumference, and the dry weight and dimensions of the grain. Notwithstanding its ubiquitous nature, the detailed relationship between AM fungal colonization and plant development is not completely understood. To facilitate a better understanding of the effects of AM fungi on plants, the work reported here assessed the effects of a consortium of AM fungi on the kernel proteome of maize, cultivated in open-field conditions. To our knowledge, this is the first report of the modulation of a plant seed proteome following AM fungal inoculation in the field. Here, it was found that AM fungi modify the maize seed proteome by up-regulating enzymes involved in energetic metabolism, embryo development, nucleotide metabolism, seed storage and stress responses.

Effects of Holder pasteurization on the protein profile of human milk

BACKGROUND

The most widespread method for the treatment of donor milk is the Holder pasteurization (HoP). The available literature data show that HoP may cause degradation of some bioactive components. The aim of this study was to determine the effect of HoP on the protein profile of human milk (HM) using a GeLC-MS method, a proteomic approach and a promising technique able to offer a qualitative HM protein profile.

METHODS

HM samples were collected by standardized methods from 20 mothers carrying both preterm and term newborns. A aliquot of each sample was immediately frozen at -80 °C, whilst another one was Holder pasteurized and then frozen. All samples were then analyzed by GeLC-MS. The protein bands of interest were excised from the gel, digested with trypsin and identified by nano-HPLC-MS/MS analysis.

RESULTS

The protein profile before and after HoP showed qualitative differences only in 6 samples out of 20, while in the remaining 14 no detectable differences were found. The differences interested only colostrums and transitional milk samples and regarded the decrease of the electrophoretic bands corresponding to alpha and beta-casein, tenascin, lactoferrin and immunoglobulin.

CONCLUSIONS

In the majority of samples, HoP did not cause any modification, thereby preserving the biological activity of HM proteins.

The arsenic hyperaccumulating Pteris vittata expresses two arsenate reductases

Enzymatic reduction of arsenate to arsenite is the first known step in arsenate metabolism in all organisms. Although the presence of one mRNA arsenate reductase (PvACR2) has been characterized in gametophytes of P. vittata, no arsenate reductase protein has been directly observed in this arsenic hyperaccumulating fern, yet. In order to assess the possible presence of arsenate reductase in P. vittata, two recombinant proteins, ACR2-His6 and Trx-His6-S-Pv2.5-8 were prepared in Escherichia coli, purified and used to produce polyclonal antibodies. The presence of these two enzymes was evaluated by qRT-PCR, immunoblotting and direct MS analysis. Enzymatic activity was detected in crude extracts. For the first time we detected and identified two arsenate reductase proteins (PvACR2 and Pv2.5-8) in sporophytes and gametophytes of P. vittata. Despite an increase of the mRNA levels for both proteins in roots, no difference was observed at the protein level after arsenic treatment. Overall, our data demonstrate the constitutive protein expression of PvACR2 and Pv2.5-8 in P. vittata tissues and propose their specific role in the complex metabolic network of arsenic reduction.

Natural Killer (NK)/melanoma cell interaction induces NK-mediated release of chemotactic High Mobility Group Box-1 (HMGB1) capable of amplifying NK cell recruitment

In this study we characterize a new mechanism by which Natural Killer (NK) cells may amplify their recruitment to tumors. We show that NK cells, upon interaction with melanoma cells, can release a chemotactic form of High Mobility Group Box-1 (HMGB1) protein capable of attracting additional activated NK cells. We first demonstrate that the engagement of different activating NK cell receptors, including those mainly involved in tumor cell recognition can induce the active release of HMGB1. Then we show that during NK-mediated tumor cell killing two HMGB1 forms are released, each displaying a specific electrophoretic mobility possibly corresponding to a different redox status. By the comparison of normal and perforin-defective NK cells (which are unable to kill target cells) we demonstrate that, in NK/melanoma cell co-cultures, NK cells specifically release an HMGB1 form that acts as chemoattractant, while dying tumor cells passively release a non-chemotactic HMGB1. Finally, we show that Receptor for Advanced Glycation End products is expressed by NK cells and mediates HMGB1-induced NK cell chemotaxis. Proteomic analysis of NK cells exposed to recombinant HMGB1 revealed that this molecule, besides inducing immediate chemotaxis, also promotes changes in the expression of proteins involved in the regulation of the cytoskeletal network. Importantly, these modifications could be associated with an increased motility of NK cells. Thus, our findings allow the definition of a previously unidentified mechanism used by NK cells to amplify their response to tumors, and provide additional clues for the emerging role of HMGB1 in immunomodulation and tumor immunity.

Effects of heavy metals and arbuscular mycorrhiza on the leaf proteome of a selected poplar clone: a time course analysis

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with the roots of most plant species. While receiving photosynthates, they improve the mineral nutrition of the plant and can also increase its tolerance towards some pollutants, like heavy metals. Although the fungal symbionts exclusively colonize the plant roots, some plant responses can be systemic. Therefore, in this work a clone of Populus alba L., previously selected for its tolerance to copper and zinc, was used to investigate the effects of the symbiosis with the AM fungus Glomus intraradices on the leaf protein expression. Poplar leaf samples were collected from plants maintained in a glasshouse on polluted (copper and zinc contaminated) or unpolluted soil, after four, six and sixteen months of growth. For each harvest, about 450 proteins were reproducibly separated on 2DE maps. At the first harvest the most relevant effect on protein modulation was exerted by the AM fungi, at the second one by the metals, and at the last one by both treatments. This work demonstrates how importantly the time of sampling affects the proteome responses in perennial plants. In addition, it underlines the ability of a proteomic approach, targeted on protein identification, to depict changes in a specific pattern of protein expression, while being still far from elucidating the biological function of each protein.

N-glycosylation of the mammalian dipeptidyl aminopeptidase-like protein 10 (DPP10) regulates trafficking and interaction with Kv4 channels

The dipeptidyl aminopeptidase-like protein 10 (DPP10) is a type II transmembrane protein homologue to the serine protease DPPIV/CD26 but enzymatically inactive. In the mammalian brain, DPP10 forms a complex with voltage-gated potassium channels of the Kv4 family, regulating their cell surface expression and biophysical properties. DPP10 is a glycoprotein containing eight predicted N-glycosylation sites in the extracellular domain. In this study we investigated the role of N-glycosylation on DPP10 trafficking and functional activity. Using site-directed mutagenesis (N to Q) we showed that N-glycosylation occured at six positions. Glycosylation at these specific residues was necessary for DPP10 trafficking to the plasma membrane as observed by flow cytometry. The surface expression levels of the substitutions N90Q, N119Q, N257Q and N342Q were reduced by more than 60%. Hence the interaction with the Kv4.3/KChIP2a channel complex was disrupted preventing the hastening effect of wild type DPP10 on current kinetics. Interestingly, N257 was crucial for this function and its substitution to glutamine completely blocked DPP10 sorting to the cell surface and prevented DPP10 dimerization. In summary, we demonstrated that glycosylation was necessary for both DPP10 trafficking to the cell surface and functional interaction with Kv4 channels.

Proteome profile and biological activity of caprine, bovine and human milk fat globules

Upon combining bidimensional electrophoresis with monodimensional separation, a more comprehensive analysis of the milk fat globule membrane has been obtained. The proteomic profile of caprine milk fat globules revealed the presence of butyrophilin, lactadherin and perilipin as the major proteins, they were also associated to bovine and human milk fat globule membranes. Xanthine dehydrogenase/oxidase has been detected only in monodimensional gels. Biological activity of milk fat globules has been evaluated in Caco2-cells, as a representative model of the intestinal barrier. The increase of cell viability was indicative of a potential nutraceutical role for the whole milk fat globule, suggesting a possible employment in milk formula preparation.

Proteomic analysis as a tool for investigating arsenic stress in Pteris vittata roots colonized or not by arbuscular mycorrhizal symbiosis

Pteris vittata can tolerate very high soil arsenic concentration and rapidly accumulates the metalloid in its fronds. However, its tolerance to arsenic has not been completely explored. Arbuscular mycorrhizal (AM) fungi colonize the root of most terrestrial plants, including ferns. Mycorrhizae are known to affect plant responses in many ways: improving plant nutrition, promoting plant tolerance or resistance to pathogens, drought, salinity and heavy metal stresses. It has been observed that plants growing on arsenic polluted soils are usually mycorrhizal and that AM fungi enhance arsenic tolerance in a number of plant species. The aim of the present work was to study the effects of the AM fungus Glomus mosseae on P. vittata plants treated with arsenic using a proteomic approach. Image analysis showed that 37 spots were differently affected (21 identified). Arsenic treatment affected the expression of 14 spots (12 up-regulated and 2 down-regulated), while in presence of G. mosseae modulated 3 spots (1 up-regulated and 2 down-regulated). G. mosseae, in absence of arsenic, modulated 17 spots (13 up-regulated and 4 down-regulated). Arsenic stress was observed even in an arsenic tolerant plant as P. vittata and a protective effect of AM symbiosis toward arsenic stress was observed.

Proteomic analysis as a tool for investigating arsenic stress in Pteris vittata roots colonized or not by arbuscular mycorrhizal symbiosis

Pteris vittata can tolerate very high soil arsenic concentration and rapidly accumulates the metalloid in its fronds. However, its tolerance to arsenic has not been completely explored. Arbuscular mycorrhizal (AM) fungi colonize the root of most terrestrial plants, including ferns. Mycorrhizae are known to affect plant responses in many ways: improving plant nutrition, promoting plant tolerance or resistance to pathogens, drought, salinity and heavy metal stresses. It has been observed that plants growing on arsenic polluted soils are usually mycorrhizal and that AM fungi enhance arsenic tolerance in a number of plant species. The aim of the present work was to study the effects of the AM fungus Glomus mosseae on P. vittata plants treated with arsenic using a proteomic approach. Image analysis showed that 37 spots were differently affected (21 identified). Arsenic treatment affected the expression of 14 spots (12 up-regulated and 2 down-regulated), while in presence of G. mosseae modulated 3 spots (1 up-regulated and 2 down-regulated). G. mosseae, in absence of arsenic, modulated 17 spots (13 up-regulated and 4 down-regulated). Arsenic stress was observed even in an arsenic tolerant plant as P. vittata and a protective effect of AM symbiosis toward arsenic stress was observed.

Proteomic analysis of Pteris vittata fronds: two arbuscular mycorrhizal fungi differentially modulate protein expression under arsenic contamination

Arbuscular mycorrhizae (AM) are the most widespread mutualistic symbioses between the roots of most land plants and a phylum of soil fungi. AM are known to influence plant performance by improving mineral nutrition, protecting against pathogens and enhancing resistance or tolerance to biotic and abiotic stresses. The aim of this study was to investigate the frond proteome of the arsenic hyperaccumulator fern Pteris vittata in plants that had been inoculated with one of the two AM fungi (Glomus mosseae or Gigaspora margarita) with and without arsenic treatment. A protective role for AM fungi colonisation in the absence of arsenic was indicated by the down-regulation of oxidative damage-related proteins. Arsenic treatment of mycorrhizal ferns induced the differential expression of 130 leaf proteins with specific responses in G. mosseae- and Gi. margarita-colonised plants. Up-regulation of multiple forms of glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and enolase, primarily in G. mosseae-inoculated plants, suggests a central role for glycolytic enzymes in arsenic metabolism. Moreover, a putative arsenic transporter, PgPOR29, has been identified as an up-regulated protein by arsenic treatment.

Effects of mercury on Dictyostelium discoideum: proteomics reveals the molecular mechanisms of physiological adaptation and toxicity

Dictyostelium discoideum amoebae were exposed to Hg 2 microM corresponding to a sublethal concentration and Hg 10 microM with the first effects on mortality and replication rate. A total of 900 spots were visualized by 2-DE electrophoresis. Two-hundred fifty single proteins were identified by mass spectrometry. Low Hg concentration (2 microM) treatment induced up-regulation of 13 spots, mainly involved in oxidative stress response/detoxification, oxidoreductase activity, and metabolic processes. High Hg concentration (10 microM) treatment showed a different PES with 12 proteins downregulated and only two up-regulated, mainly involved in cellular metabolic processes, metal ion binding, and transferase activity. The analyses for the carbonylation show no changes after 2 microM Hg(2+) treatment and 13 differentially carbonylated proteins after 10 microM Hg(2+) involved in a broad range of cellular processes. Our findings provide insight into the mechanisms of physiological adaptation and toxicity to a low and an high mercury concentration, respectively, of Dictyostelium amoebae.

Proteolysis of Milk Fat Globule Membrane Proteins in Preterm Milk: A Transient Phenomenon with a Possible Biological Role?

Milk fat globule membrane (MFGM) proteins constitute a milk fraction currently of great interest, as they appear to significantly contribute to milk protective role. We investigated these proteins in human preterm colostrum and milk. For the former we found a peculiar 2-DE pattern, with a spot concentration at low molecular weight, which mass spectrometry analysis showed to be fragments belonging to some MFGM proteins with a well-known biological and especially immunological role: lactadherin, membrane-associated lactoferrin, butyrophilin, clusterin and heavy-chain immunoglobulin. Since we were able to rule out protease activity after specimen collection, we hypothesize the localization of the proteolytic enzymes in the alveolar cell membranes of the mammary gland. This mechanism is probably under hormonal control and the unexpected advent of preterm delivery would not allow hormonal conditions typical of lactation to occur immediately, causing a delay in enzymatic inhibition. This hypothesis is supported by some of our results, picturing a peculiar transient phenomenon of adaptation of the mammary-gland-membrane proteins after preterm delivery. Further studies will be required to verify whether the presence of protein fragments exerts a specific biological and immuno-defensive role in preterm infants, thus adding evidence to the outstanding biological role and benefits of mother's own milk in feeding preterm infants.

Proteomic characterization of copper stress response in Cannabis sativa roots

Cannabis sativa is an annual herb with very high biomass and capability to absorb and accumulate heavy metals in roots and shoots; it is therefore a good candidate for phytoremediation of soils contaminated with metals. Copper is an essential micronutrient for all living organisms, it participates as an important redox component in cellular electron transport chains; but is extremely toxic to plants at high concentrations. The aim of this work was to investigate copper effects on the root proteome of C. sativa, whose genome is still unsequenced. Copper stress induced the suppression of two proteins, the down-regulation of seven proteins, while five proteins were up-regulated. The resulting differences in protein expression pattern were indicative of a plant adaptation to chronic stress and were directed to the reestablishment of the cellular and redox homeostasis.

Biochemical characterization and quantitative gene expression analysis of the multi-stress inducible metallothionein from Tetrahymena thermophila

A cadmium-binding protein with biochemical features of a metallothionein (MT) has been isolated and purified to homogeneity from the ciliate Tetrahymena thermophila. N-terminal sequencing revealed the posttranslational cleavage of the first two amino acids and, in general, a high degree of identity with known MTs from other ciliates. Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) analysis of the apothionein revealed a molecular mass (16,763 Da) higher to those of mammals and of other protozoa. Finally, quantitative real-time PCR has been used to investigate the susceptibility of this ciliate MT to gene activation in response to heavy metals and to other stressors. Our data indicate that while zinc is not effective at all and cadmium is the best inducer, other stress factors, such as mercury, copper, heat and hydrogen peroxide, also activated gene transcription. As in vertebrate cells, interleukin-6 (IL-6) that stimulates ciliate growth, was able to enhance MT gene synthesis. This complex of data seems to indicate a general role of this protein in stress response.

The proteomic approach to analysis of human milk fat globule membrane

Lactating mammary epithelial cells do not adhere to the classical rule of lipid secretion since lipids are secreted enveloped by the milk fat globule membrane (MFGM) via a budding process. Historically, biochemical studies of MFGM proteins focused on the analysis of single molecules. Today, thanks to proteomic technologies, it is now possible to comprehensively analyse the protein component of MFGM. Questions concerning: (1) protein organization within the MFGM structure; (2) correlation to the intracellular secretion pathway; and (3) display of multiple specialized functions, can now be addressed. Proteomics allows for rapid identification of the total MFGM proteins thereby providing a global functional screen of the lactating cell. In addition to their nutritional value, human MFGM proteins have important protective functions against bacteria, viruses and protozoa. Identifying the complex nature of protein-protein interactions would further enhance our present knowledge of MFGM function. A speculative molecular architecture of the human MFGM is proposed.

Structural roles of the active site iron(III) ions in catechol 1,2-dioxygenases and differential secondary structure changes in isoenzymes A and B from Acinetobacter radioresistens S13

The reversible active site metal ion removal process for two catechol 1,2-dioxygenase isoenzymes (IsoA and IsoB) isolated from Acinetobacter radioresistens S13 has been monitored using circular dichroism and fluorescence spectroscopic techniques. IsoA and IsoB are homodimers, containing one iron(III) ion per subunit. Their amino acid sequence identity is 48.4%. Previous experiments suggested that structural diversities could be responsible for the differential thermal and pH stabilities of the two isoenzymes and of their distinct demetallation kinetics. The far-UV CD spectra of IsoA and IsoB catechol 1,2-dioxygenases from A. radioresistens S13 provide information on their secondary structures. IsoB appears to have a content of alpha-helices higher than IsoA. Upon metal ion removal, both proteins reversibly lose part of their secondary structure following distinct pathways. CD spectra simulations allowed us to estimate the content of alpha-helices, beta-sheets, and turns for each isoenzyme and to monitor the secondary structure rearrangements. The metal ion withdrawal has large influence on the secondary structure: in particular a significant reduction of alpha-helices content is observed for both isoenzymes. Intrinsic fluorescence emission spectra clearly support such results, adding information on the local environment changes of the tryptophan residues. The positioning of Trp250 in IsoB has been shown to be of particular interest for monitoring the local structure changes occurring upon metal ion removal. For the first time these studies allow to underline the role of active site iron ions on dioxygenases folding and stability, further evidencing the differences in structural assembling between the two isoenzymes from A. radioresistens S13.

Effects of surface hydrophobicity on the catalytic iron ion retention in the active site of two catechol 1,2-dioxygenase isoenzymes

The different behaviour of two isozymes (IsoA and IsoB) of catechol 1,2-dioxygenase (C 1,20) from Acinetobacter radioresistens S13 on a hydrophobic interaction, Phenyl-Sepharose chromatographic column, prompted us to investigate the role of superficial hydrophobicity on structural-functional aspects for such class of enzymes. The interaction of 8-anilino-1-naphtalenesulphonate (ANS), a fluorescent probe known to bind to hydrophobic sites in proteins, revealed that the two isoenzymes have a markedly different hydrophobicity degree although a similar number of hydrophobic superficial sites were estimated (2.65 for IsoA and 2.18 for IsoB). ANS is easily displaced by adding the substrates catechol or 3-methylcatechol to the adduct, suggesting that the binding sites are in the near surroundings of the catalytic clefts. The analysis of the hydropathy profiles and the possible superficial cavities allowed to recognize the most feasible region for ANS binding. The lower hydrophobicity detected in the near surroundings of the catalytic pocket of IsoB supports its peculiarity to lose the catalytic metal ions more easily than IsoA. As previously suggested for other metalloenzymes, the presence of more hydrophilic and/or smaller residues near to the active site of IsoB is expected to increase the metal ligands mobility thus increasing the metal ion dissociation rate constants, estimated to be 0.078 h(-1) and 0.670 h(-1) for IsoA and IsoB respectively.

Structural proteome of human colostral fat globule membrane proteins

Milk fat globule membrane (MFGM) contains proteins derived from the apical membrane of secreting epithelial cells of the mammary gland. Between 2-4% of total human milk protein content is associated with the fat globule fraction, as MFGM proteins. While MFGM proteins have very low classical nutritional value, they play important roles in various cell processes and defence mechanisms for the newborn. To date, fewer than 30 human MFGM proteins have been identified and characterized, either by immunological methods or by Edman sequencing and mass spectrometry. This study aimed to update the structural proteome of human colostral MFGM proteins and to create an annotated two-dimensional electrophoresis (2-DE) MFGM protein database available on-line. More than one hundred 2-DE spots derived from human colostral MFGM proteins were investigated by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and proteins were identified by three different software packages available on the web (PeptIdent, MS-Fit and ProFound); uncertain identifications were solved by nanoelectrospray ionization-ion trap mass spectrometry using SEQUEST software.

The oxygenase component of phenol hydroxylase from Acinetobacter radioresistens S13

Phenol hydroxylase (PH) from Acinetobacter radioresistens S13 represents an example of multicomponent aromatic ring monooxygenase made up of three moieties: a reductase (PHR), an oxygenase (PHO) and a regulative component (PHI). The function of the oxygenase component (PHO), here characterized for the first time, is to bind molecular oxygen and catalyse the mono-hydroxylation of substrates (phenol, and with less efficiency, chloro- and methyl-phenol and naphthol). PHO was purified from extracts of A. radioresistens S13 cells and shown to be a dimer of 206 kDa. Each monomer is composed by three subunits: alpha (54 kDa), beta (38 kDa) and gamma (11 kDa). The gene encoding PHO alpha (named mopN) was cloned and sequenced and the corresponding amino acid sequence matched with that of functionally related oxygenases. By structural alignment with the catalytic subunits of methane monooxygenase (MMO) and alkene monooxygenase, we propose that PHO alpha contains the enzyme active site, harbouring a dinuclear iron centre Fe-O-Fe, as also suggested by spectral analysis. Conserved hydrophobic amino acids known to define the substrate recognition pocket, are also present in the alpha-subunit. The prevalence of alpha-helices (99.6%) as studied by CD confirmed the hypothized structural homologies between PHO and MMO. Three parameters (optimum ionic strength, temperature and pH) that affect kinetics of the overall phenol hydroxylase reaction were further analyzed with a fixed optimal PHR/PHI/PHO ratio of 2/1/1. The highest level of activity was evaluated between 0.075 and 0.1 m of ionic strength, the temperature dependence showed a maximum of activity at 24 degrees C and finally the pH for optimal activity was determined to be 7.5.

Phenol hydroxylase from Acinetobacter radioresistens S13. Isolation and characterization of the regulatory component

This paper reports the isolation and characterization of the regulatory moiety of the multicomponent enzyme phenol hydroxylase from Acinetobacter radioresistens S13 grown on phenol as the only carbon and energy source. The whole enzyme comprises an oxygenase moiety (PHO), a reductase moiety (PHR) and a regulatory moiety (PHI). PHR contains one FAD and one iron-sulfur cluster, whose function is electron transfer from NADH to the dinuclear iron centre of the oxygenase. PHI is required for catalysis of the conversion of phenol to catechol in vitro, but is not required for PHR activity towards alternative electron acceptors such as cytochrome c and Nitro Blue Tetrazolium. The molecular mass of PHI was determined to be 10 kDa by SDS/PAGE, 8.8 kDa by MALDI-TOF spectrometry and 18 kDa by gel-permeation. This finding suggests that the protein in its native state is a homodimer. The isoelectric point is 4.1. PHI does not contain any redox cofactor and does not bind ANS, a fluorescent probe for hydrophobic sites. The N-terminal sequence is similar to those of the regulatory proteins of phenol hydroxylase from A. calcoaceticus and Pseudomonas CF 600. In the reconstituted system, optimal reaction rate was achieved when the stoichiometry of the components was 2 PHR monomers: 1 PHI dimer: 1 PHO (alphabetagamma) dimer. PHI interacts specifically with PHR, promoting the enhancement of FAD fluorescence emission. This signal is diagnostic of a conformational change of PHR that might result in a better alignment with respect to PHO.

A proteomic approach to evaluate the butyrophilin gene family expression in human milk fat globule membrane

Human butyrophilin (BTN) expression in milk fat globule (MFGM) was evaluated using two dimensional electrophoresis (2-DE) as the separation technique, and peptide mass mapping by matrix-assisted laser desorption/ionisation-mass spectrometry (MALDI-MS) as the identification tool. Since milk composition changes throughout lactation time, 2-DE maps in the pH range 4-7 of colostral MFGM and mature MFGM were compared, showing only slight differences in BTN spot distribution. The BTN gene family codes for seven proteins (BTN, BTN2A1, BTN2A2, BTN2A3, BTN3A1, BTN3A2, BTN3A3), their presence in human tissues has to date been evaluated only at a transcriptional level. Among 70 spots, analyzed and identified by MALDI-MS, 13 spots were identified as BTN spots and only one as a fragment of BTN2A1. BTN was present in multiple glycoforms, and two smaller BTN forms of about 45 kDa were also identified. We propose an array of BTNs on human MFGM, which could provide breast-fed infants with immune molecules during the neonatal period.

Effect of hydrogen peroxide on antioxidant enzymes and metallothionein level in the digestive gland of Mytilus galloprovincialis. cavalett@unipmn.it

The pro-oxidant effect of H2O2 at a concentration of 20 microM was examined in the digestive gland of Mytilus galloprovincialis, a bivalve mollusc frequently used in biomonitoring programs. The oxidative stress caused by H2O2 has been evaluated in terms of lipid peroxidation and lysosomal system alteration. Complex cellular antioxidant defence mechanisms of the mussel were investigated at the enzymatic and non-enzymatic level in order to explain their relative role in reducing the risk of oxidative injury. Metallothionein, glutathione, superoxide dismutase, catalase and glutathione peroxidase were assayed after 1, 4 and 7 days of exposure to H2O2. The metallothionein content showed an increase by 43% after 4 days of exposure, followed by a decrease back to control values at 7 days. Antioxidant enzyme activities followed a similar pattern with a moderate increase after 1 or 4 days of treatment and a return to control values at 7 days. All data indicate a 'transient' oxidative stress response, after which mussel cells restore the redox balance.

Improved resistance to transition metals of a cobalt-substituted alcohol dehydrogenase 1 from Saccharomyces cerevisiae

Cobalt-substituted alcohol dehydrogenase 1 was purified from a yeast culture of Saccharomyces cerevisiae. Its reactivity towards different transition metals was tested and compared with the native zinc enzyme. The cobalt enzyme displayed a catalytic efficiency 100-fold higher than that of the zinc enzyme. Copper, nickel and cadmium exerted a mixed-type inhibition, with a scale of inhibition efficiency: Cu(2+)>Ni(2+)>Cd(2+). In general, a higher resistance of the modified protein to the inhibitory action of transition metals was observed, with two orders of magnitude for copper I(50). The presence of nickel in the complexes enzyme-coenzyme-inhibitor-substrate resulted in a decrease of the ampholytic nature of the catalytic site. On the contrary, cadmium and copper exerted an enhancement of this parameter. Electrostatic or other types of interactions may be involved in conferring a good resistance in the basic pH range, making cobalt enzyme very suitable for biotechnological processes.

Human proteome enhancement: high-recovery method and improved two-dimensional map of colostral fat globule membrane proteins

The human milk fat globule membrane protein composition is still largely unknown, although it counts for 2-4% of the total milk protein content and contains several important biologically active components. The aim of this work was to create a two-dimensional electrophoresis (2-DE) map of the human milk fat globule membrane proteins, both integral and membrane-associated, and to identify and characterize as many protein components as possible. A new protocol for the solubilization and extraction of the human milk fat globule membrane proteins with a double extraction procedure is presented, and the results compared with the extraction methods reported in the literature. The proteins were separated, in the first dimension, by isoelectric focusing (IEF) in the pH range 3-10 on strips of 13 cm length and, in the second dimension, by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) on 11.5% T homogeneous gels. A reproducible 2-DE map of integral and membrane-associated proteins was obtained and the first 23 spots, representing the major components, were identified by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometric analysis and/or by amino acid sequencing.

Role of metallothionein against oxidative stress in the mussel Mytilus galloprovincialis

Metallothionein (MT) is a sulfhydryl-rich protein involved mainly in heavy metal homeostasis and detoxification. In this study, the use of the mussel as an experimental model allowed us to test MT antioxidant properties at the molecular, cellular, and organism level. MT induction was achieved by mussel exposure to Cd (200 microg/l) in aquaria for 7 days followed by detoxification in the sea for 28 days. Cd-preexposed and nonexposed mussels were then treated with Fe (300-600 microg/l) in aquaria for 3 days. Biochemical assays on digestive gland tissue showed that treatment with Fe led to a significant increase in oxyradical production and malondialdehyde level only in mussels not preexposed to Cd. The Cd-dependent resistance to oxidative stress was ascribed to MT induction, as Cd produced no significant variation of reduced glutathione and major antioxidant enzymes. Digital imaging of isolated digestive gland cells showed lower oxyradical rise and higher viability in cells from Cd-preexposed mussels after treatments with 0.5-5 mM H2O2. Analyses on whole organisms showed that anoxic survival was lowered in mussels that had been treated with Fe, but such an effect was less pronounced in Cd-preexposed mussels compared with nonpreexposed ones. In conclusion, data suggest an antioxidant role for MT, which seems to occur through oxyradical scavenging and is able to protect both isolated cells and the entire organism from oxidative stress.

Phenol hydroxylase from Acinetobacter radioresistens is a multicomponent enzyme. Purification and characterization of the reductase moiety

This paper reports the isolation and characterization of phenol hydroxylase (PH) from a strain belonging to the Acinetobacter genus. An Acinetobacter radioresistens culture, grown on phenol as the only carbon and energy source, produced a multicomponent enzyme system, located in the cytoplasm and inducible by the substrate, that is responsible for phenol conversion into catechol. Because of the wide diffusion of phenol as a contaminant, the present work represents an initial step towards the biotechnological treatment of waste waters containing phenol. The reductase component of this PH system has been purified and isolated in large amounts as a single electrophoretic band. The protein contains a flavin cofactor (FAD) and an iron-sulfur cluster of the type [2Fe-2S]. The function of this reductase is to transfer reducing equivalents from NAD(P)H to the oxygenase component. In vitro, the electron acceptors can be cytochrome c as well as other molecules such as 2, 6-dichlorophenolindophenol, potassium ferricyanide, and Nitro Blue tetrazolium. The molecular mass of the reductase was determined to be 41 kDa by SDS/PAGE and 38.8 kDa by gel permeation; its isoelectric point is 5.8. The N-terminal sequence is similar to those of the reductases from A. calcoaceticus NCIB 8250 (10/12 identity) and Pseudomonas CF600 (8/12 identity) PHs, but much less similar (2/12 identity) to that of benzoate dioxygenase reductase from A. calcoaceticus BD413. Similarly, the internal peptide sequence of the A. radioresistens PH reductase displays a good level of identity (9/10) with both A. calcoaceticus NCIB 8250 and Pseudomonas CF600 PH reductase internal peptide sequences but a poorer similarity (3/10) to the internal peptide sequence of benzoate dioxygenase reductase from A. calcoaceticus BD413.

Multiple forms of lactadherin (breast antigen BA46) and butyrophilin are secreted into human milk as major components of milk fat globule membrane

In the lactating mammary gland, epithelial cells secrete triacylglycerols in the form of droplets enveloped by an apical surface membrane. This membrane is known as the milk fat globule membrane (MFGM; Mather & Keenan, 1983). MFGM-associated proteins have been studied and employed in developing antibodies against surface antigens of breast epithelial cells, which are used in breast cancer immunodiagnosis and histopathology (Salinas et al. 1987; Larocca et al. 1991; Peterson et al. 1995). So far, only a small number of proteins have been analysed and their sequence identified in bovine, murine and human MFGM; among them are butyrophilin (Jack & Mather, 1990; Ishii et al. 1995; Taylor et al. 1996), MFG-E8 (Stubbs et al. 1990), PAS 6/7 (Hvarregaard et al. 1996) and lactadherin or breast antigen BA46 (Couto et al. 1996; Taylor et al. 1997). Several minor proteins have yet to be characterized, since it is not easy to isolate them in large quantities from the membrane. SDS gel patterns give useful information about MFGM proteins, such as concentration, relative molecular mass and presence of carbohydrate. Over forty membrane components have been separated by electrophoretic techniques from bovine MFGM (Mather et al. 1980).

The research reported here combined SDS-PAGE with sequencing analysis and describes the composition of human MFGM, with the exception of high molecular mass mucin, which only penetrates an acrylamide gel of 40 g/l. Mucins have been extensively studied and the sequence predicted from cDNA (Gendler et al. 1990). Surprisingly, identification of the protein bands in the present study revealed that three proteins alone constituted the major components of human MFGM: xanthine oxidase (EC 1.1.3.22), butyrophilin and lactadherin. Lactadherin belongs to a family of proteins possessing epidermal growth factor-like and factor V/VIII C1/C2-like domains, including bovine PAS 6/7, guinea pig GP55 (Hvarregaard et al. 1996) and murine MFG-E8 (Stubbs et al. 1990). In a previous investigation, we characterized lactadherin (formerly breast antigen BA46) and its truncated 30 kDa form as components of healthy human MFGM (Giuffrida et al. 1998). Human butyrophilin has recently been cloned and sequenced (Taylor et al. 1996); the presence of two extracellular immunoglobulin superfamily domains suggested a potential cell surface receptor function. This study was aimed at identifying and characterizing the multiple forms of the major proteins of MFGM.

Absence in human milk of bovine beta-lactoglobulin ingested by the mother. Unreliability of ELISA measurements

OBJECTIVES

To analyze the presence of bovine beta-LG in breast milk.

METHODS

Human milk samples from 14 healthy non-atopic women on diets with different cow's milk contents were examined. The total concentration of beta-LG immuno-like proteins (beta-LGIP) was determined by enzyme linked immunosorbent assay (ELISA). Identification of antigens was done by N-terminal sequencing.

RESULTS

beta-LGIP reactivity of the milk from subjects on different diets was not significantly different. Human lactoferrin, beta-casein and alpha-lactalbumin, were identified as cross-reacting antigens.

CONCLUSIONS

False-positive results in ELISA determinations of bovine beta-LG in human milk might be due to cross-reactions between polyclonal antibodies and different protein antigens.

Isolation and characterization of full and truncated forms of human breast carcinoma protein BA46 from human milk fat globule membranes

We have isolated and characterized two proteins of 50 and 30 kDa from human milk fat globule membranes of healthy donors. N-terminal and internal sequencing revealed that the 50-kDa protein is the full-length human breast carcinoma protein BA46 that is highly expressed in human breast tumors. The 30-kDa protein is a truncated form of protein BA46 which consists of the C-terminal factor V/VIII-like domain of BA46 and which appears to anchor BA46 to the milk fat globule membrane. Defective release of the epidermal growth factor domain containing a surface RGD motif may be related to involvement of BA46 in breast cancer.

The unusual amino acid triplet Asn-Ile-Cys is a glycosylation consensus site in human alpha-lactalbumin

Human alpha-lactalbumin has not been described as a glycoprotein, despite the fact that several alpha-lactalbumins of both ruminant and nonruminant species are known to be glycosylated. In all these species the glycosylation site is the 45Asn in the usual triplet 45Asn-Gly/Gln-47Ser. We have found that human alpha-lactalbumin is glycosylated and the glycosylation site has been determined by protein sequencing and mass spectrometry. We report an unusual glycosylation site at 71Asn in the triplet 71Asn-Ile-73Cys, which is conserved in all known alpha-lactalbumins except red-necked wallaby. That a relatively small proportion of the protein is glycosylated (about 1%) may reflect the importance of this region of the protein sequence to the molten globule state of alpha-lactalbumin.

Human milk proteins may interfere in ELISA measurements of bovine beta-lactoglobulin in human milk

It is widely believed that cow's milk proteins ingested by the mother, in particular beta-lactoglobulin (beta-LG), can pass into breast milk and thus sensitize predisposed infants. However, studies to evaluate bovine beta-LG in human milk have given conflicting results. The aim of this study was to analyse the correlation between the amount of cow's milk in the mother's diet and the presence of bovine beta-LG in breast milk. Human milk samples from 14 healthy non-atopic women on diets with different cow's milk contents were examined. The total concentration of bovine beta-LG or beta-LG immuno-like proteins (beta-LGIP) was determined by enzyme-linked immunosorbent assay (ELISA). Two separation procedures utilizing ELISA plates and an affinity chromatography column were set up to identify the human whey components recognized by the anti-beta-LG antibodies. beta-LGIP reactivities of milk from three groups on different diets were not significantly different. After splitting the antigen-antibody complexes, three main protein components, human lactoferrin, human beta-casein and human alpha-lactalbumin, were identified. This study would suggest that, at least in healthy subjects, false-positive results in ELISA determinations of bovine beta-LG in human milk might be due to cross-reactions between polyclonal antibodies and different protein antigens.

Human alpha S1-casein like protein: purification and N-terminal sequence determination

Casein components of human milk are generally reported to belong to the beta- and kappa-groups. In this research human casein fraction was obtained from pooled mature milk, either by ultracentrifugation or by acid precipitation. In both cases a minor component with a slightly higher mobility in SDS-PAGE than beta-casein was identified. The protein was purified to homogeneity, the N-terminal sequence of the first 14 amino acid residues of this new human casein subunit shows a high degree of homology with the alpha s1-casein sequences from other species.

Modulation of Na+/K+ pump in intact erythrocytes by cardioglycosides, steroid hormones and ouabain-like compounds

1. Pure erythrocytes preparations, free from platelets and white cells, were incubated for a long time without hemolysis. 2. Dose-response experiments performed with (a) cardioglycosides (ouabain and K-strophantoside), (b) steroid hormones and their glucuronides (tetrahydrocortisol, oestradiol and the respective 3-glucuronic derivatives) and (c) ouabain-like compounds purified in our laboratory (0.7 kDa and 2-4 kDa respectively) emphasise a modulatory effect [activation of Na+ efflux rate and K+ uptake at very low ligand concentrations, inhibition at higher levels; maximum enhancement of cation transport: (a) and (b) 10-0.1 nM (+40-50%), (c) 1-0.01 nM (2.5-fold)]. 3. Binding experiments show upward-curved Scatchard graphs, with the Kd values of 50 nM and 18 microM and the Bmax values of 10.2 and 984.5 fmol/100 microliters RBC (red blood cells) respectively.

Modulatory effect of two cardioglycosides on reconstituted Na+/K(+)-ATPase in proteoliposomes

1. Na,K-ATPase was extracted from Cavia cobaya kidneys, solubilized with nonionic detergent C12E8 (octaethyleneglycol dodecyl monoether) in mixed lipid-detergent-protein micelles. The Na,K-ATPase specific activity was 30-35 IU/mg protein. 2. The enzyme was reconstituted in vesicles, made of phosphatidylethanolamine and cholesterol: an enhancement of +60% in specific activity was obtained. 3. Two different vesicle-types were carried out: open liposomes (partially organized membranes) and closed liposomes. 4. Proteoliposomes were employed for measuring the modulatory effect of two cardioglycosides: ouabain and digoxin. 5. Inhibition of the Na,K-ATPase activity revealed apparent Ki of 1.25 microM for ouabain and 0.25 microM for digoxin in open liposomes, and apparent Ki of 0.75 microM for ouabain and of 1.75 microM for digoxin in closed liposomes. 6. Maximum enhancement of enzymatic activity was found at concentrations of 5-0.5 nM for ouabain and 5-1 nM for digoxin in open liposomes, and 25-1 nM for both digoxin and ouabain in closed liposomes.

Extraction, purification and characterization of ADH1 from the budding yeast Kluyveromyces marxianus

The enzyme ADH1 has been extracted and purified from the budding yeast Kluyveromyces marxianus, and its enzymatic activity has been compared, with the ADH1 extracted and purified in the same way from the well known yeast Saccharomyces cerevisiae. K. marxianus ADH1 has an optimal temperature higher than the S. cerevisiae enzyme (45-50 degrees vs 35 degrees C), a better stability to pH variations in the oxidative reaction (pH optimum 7.5), a lower Michaelis constant for acetaldehyde, and a good catalytic activity both for fermentative and oxidative reactions. In fact, while in Saccharomyces the constants ratio (velocity constant fermentation/velocity constant oxidation) is about 20,000, in Kluyveromyces the same ratio is only 15. Even if these two Genera are quite related (they belong to the same subfamily) it seems that their ADH1s possess different catalytic properties.

Modulatory effect of some steroid hormones, their glucuronides and ouabain-like compounds on Cavia cobaya kidney Na+,K(+)-ATPase activity

1. Ouabain-like compounds (approx. mol. wt 700, 2,000 and 4,000 Da) were purified from plasma of essential hypertensive patients. 2. Dose-response experiments performed with (a) steroid hormones, (b) their glucuronides and (c) ouabain-like compounds, emphasize a modulatory effect [activation of the Na,K-ATPase at very low concentrations of ligand, inhibition at higher levels; apparent Ki: (a) between 1 and 0.5 mM; (b) between 1 and 0.5 microM; and (c) between 10 and 1 nM; maximum enhancement of the enzymatic activity: (a) +20%; (b) +45%; and (c) +100%]. 3. Displacement experiments of [3H]ouabain evidence a high competition of the ligands towards the cardioglycoside. The relative I50s are: (a) between 1 and 0.5 mM; (b) between 10 and 1 microM; and (c) between 10 and 0.01 nM.