Antiallergic activity of novel isoflavone methyl-glycosides from Cordyceps militaris grown on germinated soybeans in antigen-stimulated mast cells

Isoflavones are known to possess immunomodulating and antiallergic activities. Previously we identified novel isoflavone methyl-glycosides (daidzein 7-O-β-d-glucoside 4″-O-methylate (CDGM), glycitein 7-O-β-D-glucoside 4″-O-methylate (CGLM), genistein 7-O-β-D-glucoside 4″-O-methylate (CGNMI) and genistein 4'-O-β-D-glucoside 4″-O-methylate (CGNMII)) from Cordyceps militaris grown on germinated soybeans (GSC). The biological activity of novel isoflavone methyl-glycosides, however, remains unknown. In this study, CGNMII showed the strongest inhibition of degranulation. Additionally, the release of interleukin (IL)-4 and tumor necrosis factor (TNF)-α was decreased by CGNMII in antigen-stimulated RBL-2H3 cells. To elucidate the antiallergic mechanism of CGNMII, we examined whether it affected levels of signaling molecules responsible for degranulation. The levels of activated Lyn, Syk, PLCγ1 and LAT proteins were reduced in CGNMII treated RBL-2H3 cells. CGNMII also inhibited the activation of AKT and ERK1/2 proteins. These results suggest that CGNMII might be used as a therapeutic agent for allergic diseases.

Secondary metabolites and insecticidal activity of Anemone pavonina

The insecticidal properties of the crude extracts of the leaves and flowers of Anemone pavonina were evaluated on Pheidole pallidula ants and showed significant levels of activity. Bioassay-guided fractionations led to the isolation of the butenolide ranunculin (1) as the active principle. Chemical investigations of the extracts showed them to contain as major components the sitosterol glycopyranoside lipids 2-5 and the glycerides 6-8. The structures of the metabolites were elucidated, following acetylation and hydrolysis of the natural products, by interpretation of their NMR and mass spectral data. The uncommon lipid metabolites 2-8 were isolated for the first time from the genus Anemone and this is the first report of insecticidal activity of the Anemone metabolite ranunculin against ants.

β-Methyl-xyloside: positive effect on xylanase induction in Cellulomonas flavigena

Synthesis of extracellular xylanase in Cellulomonas flavigena is induced in the presence of xylan and sugarcane bagasse as substrates. The essential factors for efficient production of xylanase are the appropriate medium composition and an inducing substrate. The increase in xylanase production levels in C. flavigena were tested with a number of carbon sources and different culture conditions. Xylose, arabinose, glycerol and glucose did not induce xylanase production in this microorganism. beta-Methyl-xyloside (beta-mx), a structural analog of xylobiose, also did not induce xylanase when used as the sole carbon source, but when xylan or sugar cane bagasse was supplemented with beta-mx, extracellular xylanase production increased by 25 or 46%, respectively. The response of C. flavigena to xylan plus beta-mx was accompanied by a significant accumulation of reducing sugar, an effect not observed with the combination sugarcane bagasse plus beta-mx as substrate. To our knowledge, this is the first report on the effect of beta-mx on the induction of xylanase in C. flavigena.

Further evidence for the gelation ability-structure correlation in sugar-based gelators

Eight methyl glycosides of 4,6-O-benzylidene derivatives of the monosaccharides D-glucose, D-mannose, D-allose and D-altrose were synthesized to systematically study the effect of small configurational changes on the ability to gelate organic solvents. Among the beta anomers, only the D-mannose glycoside exhibits a strong gelation ability, whereas in the alpha-series the D-glucose and D-mannose derivatives act as versatile gelators. Also, as a general rule we found that the beta anomers possess a higher ability to gelate solvents than the alpha anomers. The gelation properties are discussed on the basis of SAXS, FTIR, differential scanning calorimetric (DSC) measurements and scanning electron microscopy (SEM) observations. The temperature-dependent SAXS measurements were carried out to elucidate the sol-gel transition temperature. The present study emphasizes that the saccharide family provides, not only valuable information of the structural requirements for the design of new gelators, but also for molecular assembly systems in general.

Adherence of Mycoplasma pneumoniae to human alveolar macrophages

The human pathogen Mycoplasma pneumoniac causes primary atypical-cold agglutinin-positive pneumonia. Since alveolar macrophages internalize mycoplasma as part of their immune defense, we studied characteristics of the human macrophage receptor for opsonized and nonopsonized M. pneumoniae. The glass-adhering subpopulation of M. pneumoniae attached more than the non-adherent subpopulation. The attachment was dose-dependent and enhanced by opsonization in the presence of human serum. It is inhibited by sulfated compounds such as dextran-sulfate and polyanetholsulfonic acid, but not by dextran or several monosaccharides, suggesting that sulfated glycolipids on the macrophage surface may act as receptors for M. pneumoniae binding. In addition, sialylated compounds, such as fetuin and alpha 1-acid glycoprotein, were found to be potent inhibitors of the attachment, also indicating the role of sialic acid residue in recognition and attachment of M. pneumoniae to human alveolar macrophages.

Substrate specificity of small-intestinal lactase. Assessment of the role of the substrate hydroxyl groups

Lactase-phlorizin hydrolase is a disaccharidase present in the small intestine of mammals. This enzyme has two active sites, one being responsible for the hydrolysis of lactose. Lactase activity is thought to be selective towards glycosides with a hydrophilic aglycon. In this work, we report a systematic study on the importance of each hydroxyl group in the substrate molecule for lactase activity. For this purpose, all of the monodeoxy derivatives of methyl beta-lactoside and other lactose analogues are studied as lactase substrates. With respect to the galactose moiety, it is shown here that HO-3' and HO-2' are necessary for hydrolysis of the substrates by lactase. Using these chemically modified substrates, it has been confirmed that lactase does not behave as a typical beta-galactosidase, since it does not show an absolute selectivity with respect to substitution and stereochemistry at C4' in the galactose moiety of the substrate. However, the glucose moiety, in particular the HO-6, appears to be important for substrate hydrolysis, although none of the hydroxyl groups seemed to be essential. In order to differentiate both activities of the enzyme, a new assay for the phlorizin-hydrolase activity has also been developed.

Studies on pH regulatory mechanisms in cultured astrocytes of DBA and C57 mice

pH regulatory mechanisms in primary cultures of astrocytes from the cerebral cortex of neonatal audiogenic-seizure-susceptible DBA/2J (DBA) and genetically controlled C57BL/6J (C57) mice were studied with [14C]dimethyloxazolidine-2-4-dione (DMO) and [3H]-methyl-D-glucose (MDG). Effects of changing the concentration of Na+, K+, HCO3- or Cl- in medium, and/or of different transport blockers and metabolite inhibitor on intracellular pH (pHi) of cultured astrocytes were also studied. In nominal HCO3(-)-free HEPES-buffered Hanks' balanced salt solution (HEPES HBSS), when the pH of medium (pHo) was maintained at 7.4, the steady-state pHi of cultured astrocytes from DBA mice was 6.98 +/- 0.03, and that from C57 mice was 7.01 +/- 0.03. When the cells were incubated in HBSS containing 25 mM HCO3- and equilibrated with 5% CO2 (HCO3- HBSS, pHo = 7.4), pHi of both DBA and C57 astrocytes was approximately 0.1-0.15 pH units higher than that in HEPES HBSS. Reducing the pH or the Na+ concentration in media (pHo, [Na+]o) of either HEPES HBSS or HCO3- HBSS, pHi of both DBA and C57 astrocytes decreased markedly (0.25-0.45 pH units lower than the controls). The decrease in pHi was greater in HEPES HBSS than in HCO3- HBSS. Reducing the Cl- concentration ([Cl-]o) in either HEPES or HCO3- HBSS, pHi of astrocytes increased by 0.05-0.1 pH units. Increasing the K+ concentration ([K+]o) of or adding Ba2+ to the media increased the pHi of both DBA and C57 astrocytes accordingly. SITS, an anion transport inhibitor, decreased the pHi of both DBA and C57 astrocytes in HCO3- HBSS but not in HEPES HBSS. It enhanced the response of pHi to reduction in pHo. Amiloride, a Na(+)-H+ exchange inhibitor, decreased the pHi of both DBA and C57 astrocytes more in HEPES HBSS than in HCO3- HBSS. It enhanced the response of pHi to reduction in pHo and [Na+]o. Ouabain, an Na+,K(+)-ATPase inhibitor, decreased the pHi of cultured astrocytes in HEPES HBSS, but not in HCO3- HBSS. It also enhanced the response of pHi to changing pHo and [Na+]o in HEPES HBSS. Acetazolamide, a carbonic anhydrase inhibitor, decreased the pHi of astrocytes in both HEPES and HCO3- HBSS. Both bumetanide, an Na+,K+/Cl- cotransport blocker, and KCN, a metabolic inhibitor, produced no significant effect on the steady-state pHi or the response of pHi to changing ionic concentration in media in both DBA and C57 astrocytes.

Free-radical synthesis of 3-(2-cyanoethyl)- and 3-(2-methoxycarbonylethyl)-2,3-dideoxy-alpha-D-erythro-pentofu ranoside and their application in the synthesis of potential antiviral nucleosides

Free-radical reaction of different carbohydrate educts 2, 5, and 7 with acrylonitrile in the presence of tributyltin hydride and a radical initiator (AIBN) gave the methyl 3-(2-cyanoethyl)-2,3-dideoxypentofuranosides 3a and 6. Similar reaction of 2 with methyl acrylate gave 3-(2-methoxycarbonylethyl)-2,3-dideoxypentofuranose 3b. Nucleoside coupling of 3a with silylated uracil gave an anomeric mixture of beta- and alpha-nucleoside 8 and 9 which were deprotected to give 10 and 11, respectively. Similar reaction of 3b with silylated N4-isobutyrylcytosine gave 12 and 13 which were deprotected to give the final nucleosides 16 and 17, respectively. None of the compounds 10a, 11, 14-17 showed significant activity against HIV.

Derivatives of methyl beta-lactoside as substrates for and inhibitors of beta-D-galactosidase from E. coli

The 2'-,4'-, and 6'-deoxy derivatives of methyl beta-lactoside have been synthesised by deoxygenation at positions 2', 4', and 6', and the 3'-deoxy derivative was obtained by a glycosylation reaction. The 2'-O-methyl, 2'-O-benzyl, 2'-amino-2'-deoxy, and 1'-deuterio derivatives have been synthesized also. Only the 6'-deoxy and 1'-deuterio derivatives were substrates for the beta-D-galactosidase from E. coli, and the 2'-deoxy- and 2'-amino-2'-deoxy derivatives were potent inhibitors for the hydrolysis of methyl beta-lactoside by the enzyme.

Whole cell recording of sugar-induced currents in LLC-PK1 cells

Gigaohm-seal whole cell recording techniques were used to monitor function of the Na(+)-coupled sugar transport system in LLC-PK1 cells. The currents coupled to sugar transport were identified as those that are induced by the presence of 10 mM alpha-methylglucoside (AMG) in either the extracellular or intracellular compartment and were inhibited by addition of 320-800 microM phlorizin to the extracellular bathing medium. The sugar-induced currents are small, 15-20 pA, but of the expected magnitude as determined from the known kinetic parameters for Na(+)-coupled sugar transport in LLC-PK1 cells. The phlorizin-sensitive currents are Na+ dependent and can be studied under conditions in which the net Na+ and sugar flux (and consequently the Na+ electrical current) is in either the inward or outward direction. The reversal potential of the sugar-induced currents measured under conditions with high Na+ and AMG concentrations inside the cell is close to values predicted from thermodynamic principles, assuming a coupling stoichiometry of 2 Na+: 1 sugar for the transport system. The reversal potential of the sugar-induced currents with high extracellular Na+ and AMG is not equal to the predicted value, but it is of the polarity expected for inward-imposed solute gradients. Reasons for the observed discrepancy between observed and calculated values are discussed.

Sugar-dependent selective induction of mouse jejunal disaccharidase activities

1. Sugar-containing diets chosen not to affect intestinal structure or enterocyte turnover have been fed to mice previously maintained on a low carbohydrate diet in order to determine their ability to induce disaccharidase enzymes in the small intestine. 2. Glucose-, fructose- and 3-O-methyl-glucose-containing diets increased sucrase and maltase but not lactase activities in mouse jejunal homogenates. These effects were either absent or negligible in more distal regions of the small intestine. 3. Placing mice on glucose-, fructose- or 3-O-methyl-glucose-containing diets was further shown, by quantitative cytochemistry, to cause a 1.6-, 2.6- and 3.2-fold increase in the initial rate at which alpha-glucosidase activity (sucrase + maltase) appeared in the brush-border membrane of developing enterocytes. 4. The time during which alpha-glucosidase activity increased in enterocyte brush-border membranes fell from 30 h for low carbohydrate fed mice to 21, 19 and 17 h in mice fed glucose, fructose and 3-O-methyl-glucose respectively. Change of diet had no effect on the kinetics of lactase expression by developing enterocytes. 5. Maximal alpha-glucosidase activity detected in enterocyte brush-border membranes is equal to RT, where R is the initial rate of enzyme appearance and T is the time during which this rate operates. The ability of sugars to increase R selectively, but only at the expense of T, defines unexpected limits to the capacity of enterocytes to adapt to changes in luminal nutrition. 6. The above results are discussed in relation to other aspects of enterocyte differentiation recently subjected to quantitative analysis. The need to standardize other aspects of intestinal physiology and redefine the energy content of diets containing non-metabolizable substrates in this type of work is also emphasized.

The role of glucose uptake and metabolism in hyperglycemic exacerbation of neurological deficit in the paraplegic rat

Previous studies indicate that hyperglycemia, particularly that induced by exogenous glucose administration, exacerbates neurological deficits in the rat spinal cord ischemic model. The effect of inhibition of glucose uptake (glucose transporter) and initial metabolism (hexokinase) on neurological outcome was evaluated in the present investigation using the competitive inhibitors 2-deoxyglucose (2-DG) and 3-O-methylglucose (3-OMG). Sprague-Dawley rats, weighing 200 to 300 gm each, received either 0.25, 1, or 2 gm/kg 2-DG; 2 gm/kg 3-OMG; 2 gm/kg glucose; or an equivalent volume of 0.9% saline intraperitoneally. Rats were intubated and ventilated with 1% to 1.5% halothane. The aortic arch was exposed and snares were placed on the right and left subclavian arteries and the aorta distal to the left subclavian artery. The three vessels were occluded for 10, 11, 12, or 13 minutes. Lower-extremity neurological deficits were evaluated at 1, 4, 18, and 24 hours postocclusion based on a 15-point scale (normal = 0, severe deficit = 15). Lower-extremity neurological deficits were significantly less severe in the groups treated with 2-DG (0.25 and 1 gm/kg) at 18 and 24 hours postocclusion (p less than 0.05 for 0.25 gm/kg and p less than 0.005 for 1 gm/kg, Student's t-test with Bonferroni correction). The lower 2-DG dose of 0.25 gm/kg did not significantly increase the plasma glucose level, suggesting that the glucose transporter was not markedly inhibited, and that the improved neurological outcome was more likely due to inhibition of hexokinase. The higher 2-DG dose of 1 gm/kg afforded protection despite significantly increasing the plasma glucose level, implying a strong inhibition of both the glucose transporter and hexokinase. Administration of 3-OMG, which only inhibits glucose uptake and not hexokinase, actually worsened the neurological deficit in a manner similar to that observed in rats treated with glucose. The authors conclude that the activity of the glucose transporter by itself does not significantly contribute to hyperglycemic exacerbation of neurological deficits. In contrast, the hexokinase step, at least in combination with the transporter and possibly alone, plays a significant role in hyperglycemic exacerbation of the lower-extremity neurological deficit in the paraplegic rat.

Effects of inhibition of proteoglycan synthesis on the differentiation of cultured rat Schwann cells

Schwann cells synthesize two heparan sulfate proteoglycans, one that is a component of the Schwann cell basement membrane and a smaller one that is an integral component of the Schwann cell plasma membrane. To determine the functions of these molecules, Schwann cell-nerve cell cultures were grown in medium containing a specific inhibitor of proteoglycan biosynthesis, 4-methylumbelliferyl-beta-D-xyloside. Treatment with 1 mM beta-D-xyloside caused a 90% reduction in the accumulation of 35SO4-labeled proteoglycans in the cell layer of the cultures. Gel filtration analysis revealed that both the basement membrane and plasma membrane proteoglycans were affected. Inhibition of proteoglycan biosynthesis was accompanied by an inhibition of laminin deposition into extracellular matrix as determined by immunostaining of cultures and by immunoblotting of cell-associated proteins. This occurred even though there was no decrease in the amount of laminin detected in the medium of beta-D-xyloside-treated cultures. Deposition of collagen type IV was similarly affected. In addition, there was no myelin produced in beta-D-xyloside treated cultures. However, when beta-xyloside-treated cultures were supplied with exogenous basement membrane, Schwann cells produced numerous myelin segments. These results indicate that Schwann cell proteoglycans play an essential role in basement membrane assembly, and that the integral plasma membrane proteoglycan is not required for the basement membrane to exert its effects on Schwann cell differentiation.

Prevention of streptozotocin-induced alterations in the rat heart by 3-O-methyl glucose and insulin treatments

Streptozotocin-induced diabetes has previously been shown to alter the sensitivity and responsiveness of rat myocardial tissues to cardiotonic agonists. The objective of the present study was to determine if these alterations were due to the diabetogenic or possible direct cardiotoxic effects of streptozotocin. One month after streptozotocin treatment the following changes were observed in the rat: decrease in body weight; elevation of blood glucose and glycosylated hemoglobin levels; decrease in spontaneously beating atrial rate; elevation in basal developed force of electrically driven right ventricle; and inotropic subsensitivity of right ventricle to isoproterenol, which was associated with decreased beta-adrenoceptor density and supersensitivity to calcium. Pretreatment with the nonmetabolizable glucose analog 3-O-methyl glucose prevented these alterations. Chronic insulin replenishment also reversed the effects of streptozotocin, with the exception of complete normalization of elevations in blood glucose and basal developed force. Acute exposure to high glucose in the medium preserved the subsensitivity to isoproterenol but resulted in an elevated basal developed force in both control and streptozotocin groups. These observations indicate that myocardial alterations after streptozotocin treatment are not the result of direct cardiotoxic effects but rather a consequence of the drug-induced diabetic state. They also suggest that the increase in basal developed force might be related to elevated glucose concentrations.

Effect of pharmacological doses of 3-0-methyl-D-glucose and 2-deoxy-D-glucose on rat brain glucose and lactate

The present investigation examined the effects of two glucose analogues, 3-0-methyl-D-glucose (30MG) and 2-deoxy-D-glucose (2DOG) on basal levels of rat brain glucose and lactate. The results showed that pretreatment (iv) with 30MG up to 2 g/kg caused a transient drop in brain glucose levels to 42% of control value within 2.5 min and a drop in lactate levels to 75% of control value by 5 min. 2DOG administration (2 g/kg) affected glucose in a biphasic response with an initial drop to 46% of control value seen by 2.5 min, followed by a progressive increase to 290% of the control value by 40 min. This elevated level of glucose was sustained for approximately 40 min. Lactate levels responded to 2DOG administration by a decrease to 37% of control value within 10 min post-injection and returned to near basal levels by 160 min. A dose response was also examined for both compounds. Behaviorally 30MG had no apparent effects. However, the response to 2DOG was a reduction in voluntary movements, piloerection, irregular clonic jerks, splayed limbs and fits of wild running. These experiments were designed to evaluate the potential of 30MG or 2DOG for attenuating the well documented rise in brain lactate levels following an ischemic insult. Our results suggest that under certain experimental conditions either 30MG or 2DOG could prevent brain lactate rise and might have beneficial effects in minimizing the neuropathological consequences of ischemic damage that could be related to increases in brain lactate.

A structure-activity study on the sucrose taste antagonist methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside

In order to assess the effect of the antagonist methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside (MAD-diCl-Gal) upon the gerbil's chorda tympani sucrose taste response, we tested several concentrations of this compound, as well as single concentrations of closely related derivatives, and found that MAD-diCl-Gal was the most potent inhibitor tested. It appears that the inhibition mechanism is very specific. For example, we have found that 2 chlorine atoms at the C-4 and C-6 positions on the glucopyranoside ring are required for inhibition. In addition, with regard to the orientation of the chlorine atoms, the galacto derivative seems to be more potent than the gluco derivative. We have also found that the methyl glycoside is more potent than the free sugar. With regard to the orientation of the methyl group, MAD-diCl-Gal is more potent than its beta-anomer. (Because of this discovery of the methyl group enhancement and orientation effect, we shall discontinue using the acronym diCl-Gal and replace it with the more specific MAD-diCl-Gal.) Of particular significance is the fact that there appears to be a structure-activity relationship between the most active stimulants and inhibitors in that the requirement for an axial orientation at C-1 and the enhancement by the methyl group at that position are the same in both cases. These results suggest that both the stimulator and the antagonist are acting at the same receptor site.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular matrix proteoglycans and cell-substratum adhesion of human endothelial cells: the effect of methyl beta-D-xylopyranoside

The influence of methyl beta-D-xylopyranoside on human endothelial cell proteoglycans isolated from the medium and extracellular matrix was investigated. Confluent cultures of human endothelial cells incorporate significant amounts of heparan sulfate (78%), chondroitin sulfate (10%), and dermatan sulfate (12%) into the extracellular matrix. Chondroitin sulfate (35%) and dermatan sulfate (37%) were the major glycosaminoglycans present in the medium. In the presence of methyl beta-D-xylopyranoside, incorporation of labeled proteoglycans into extracellular matrix was diminished by approximately 70%. Heparan sulfate comprised the major proteoglycan present in extracellular matrix (89%) in cells grown in the presence of methyl beta-D-xylopyranoside. In contrast to the incorporation of proteoglycan into extracellular matrix, methyl beta-D-xylopyranoside stimulated the secretion of labeled glycosaminoglycan chains into the medium 2.5-fold. In the presence of methyl beta-D-xylopyranoside, secretion of chondroitin sulfate into the medium was markedly stimulated, with a slight increase in secretion of heparan sulfate. Chondroitin sulfate (62%) and heparan sulfate (34%) were the major labeled glycosaminoglycans present in medium from methyl beta-D-xylopyranoside-treated cultures. The effect of methyl beta-D-xylopyranoside on cell adhesion and detachment was investigated. Cell detachment from extracellular matrix depleted of proteoglycan was significantly faster than detachment from normal matrix. Conversely, human endothelial cells adhered faster to normal matrix than to matrix depleted of proteoglycan.

Plasmodium falciparum: carbohydrates as receptor sites of invasion

Monosaccharides, disaccharides, and trisaccharides were tested as inhibitors of the in vitro growth of Plasmodium falciparum (strain FCB). While certain monosaccharides (N-acetyl-D-glucosamine, D-mannose, and 3-O-methyl-D-glucose) proved to exhibit a toxic or reversibly retarding effect on the intraerythrocytic development of the parasite, the corresponding alpha- or beta-methylglycosides did not. Several methylglycosides, synthetic di- and tri-saccharides, and artificial blood group antigens were further tested for inhibitory effects on invasion of host red blood cells in vitro. The synthetic disaccharides beta DGlcNAc(1----4) alpha DManOMe and beta DGlcNAc(1----4) DGlcNAc (chitobiose) were good inhibitors of invasion at 10 mM concentration, whereas beta DGal(1----4)beta DGlcNAcOMe was negligibly inhibitory. The inhibition rate of N-acetyl-D-glucosamine, beta-glycosidically linked to bovine serum albumin (BSA) by an alipathic spacer, -(CH2)8CO-, was not enhanced, compared to the corresponding hapten, beta DGlcNAcO(CH2)8COOCH3. The inhibition rates of blood group A- and B-trisaccharide haptens, which were inhibitors of invasion, were also not significantly enhanced when coupled to BSA by way of the corresponding amide spacer, -(CH2)2NHCO(CH2)7CO-. A remarkable enhancement of the inhibition rate was, however, observed when beta DGal(1----3) alpha DGalNAcO(CH2)2NHCO(CH2)7COOCH3 (T-hapten) was coupled to BSA. A clear-cut decrease in the inhibition rates of different beta-glycosides of N-acetyl-D-glucosamine, beta DGlcNAcOR, was observed, depending on the nature of the aglycon R(p-nitrophenyl greater than -(CH2)8COOCH3 greater than -(CH2)2NHCO(CH2)2COOCH3 greater than -CH3). Also, p-nitrophenyl-alpha-D-glucopyranoside was a much better inhibitor of invasion than the corresponding methyl glycoside, alpha DGlcOMe, which was not inhibitory. The properties of the aglycon spacer, used for the covalent attachment of the carbohydrate to the carrier protein, may thus be crucial for the outcome of the inhibition rate.

Calcium-dependent aggregation of human serum amyloid P component. Inhibition by the cyclic 4,6-pyruvate acetal of galactose

Serum amyloid P component is a normal plasma glycoprotein which is the precursor of amyloid P component, a minor but universal constituent of amyloid deposits. When isolated human P component is exposed to free ionised Ca2+ it aggregates and precipitates. This phenomenon is completely inhibited by the presence of 10(-4)-10(-2) M methyl 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranoside, a recently synthesised specific ligand for amyloid P component. This observation suggests that the autoaggregation of human amyloid P component involves the Ca2+ dependent specific ligand binding property of P component, but does not distinguish between receptor-site-mediated and allosteric mechanisms.

Effect of serine hydroxamate and methyl alpha-D-glucopyranoside treatment on nucleoside polyphosphate pools, RNA and protein accumulation in Streptomyces hygroscopicus

The accumulation of RNA and protein and the kinetics of nucleoside triphosphate and guanosine polyphosphate pools during amino acid starvation and carbon source downshift were investigated in Streptomyces hygroscopicus. RNA accumulation was controlled stringently during both amino acid starvation and carbon source downshift. The pool size of ppGpp increased dramatically under these conditions. However, the intracellular concentrations of nucleoside triphosphates were low and the concentration of guanosine polyphosphates was much lower than in Escherichia coli. The possible significance of this phenomenon in the regulation is discussed.

Release of cell-associated concanavalin A by methyl alpha-D-mannopyranoside reveals three binding states of concanavalin-A receptors on mouse fibroblasts

Based on the partial reversibility of concanavalin A binding by saturating concentrations of methyl alpha-D-mannopyranoside (MeManp) three states of cellular association could be characterized: type I, most rapidly established and most tightly bound, not released by MeManp at 0 degrees C or at 37 degrees C; type II, most loosely bound, released by MeManp at 0 degrees C, therefore not critically dependent on the temperature at which the release reaction is performed; type III, intermediate strength of binding, released by MeManp only at 37 degrees C, thus reflecting the temperature-sensitive nature of these cell complexes. A similar temperature dependence was found for cell-bound concanavalin A when it was displaced by an excess of the same lectin. The types of binding are seen irrespective of the temperature at which the cellular association was established. About 10% of the concanavalin A molecules bind to receptor structures in a saturable way and represent the type I association. Type I association is clearly distinct from types II and III. Type II seems to be the precursor of type III. Most of the type II associations can be converted into type III associations since ConA-cell complexes originally sensitive to the action of MeManp at low temperature gradually do become resistant after prolonged association at the same temperature. The temperature dependence in binding to cells was, however, not related to receptor mobility since glutaraldehyde-treated cells had most of the release properties that were observed in untreated cells and which did not markedly differ between 3T3 cells and their SV40-transformed counterparts. In contrast to cellular binding, dissociation of concanavalin A from Sephadex beads by saturating concentrations of MeManp was complete irrespective of temperature.

Suppression of T cell cytotoxicity by nude mouse spleen cells: reversal by monosaccharides and interleukin 2

The effects of monosaccharides on the suppression of cytotoxic T cell generation by spleen cells from nu/nu mice were examined. Suppression of the B6 anti-BALB/c response and the B6 anti-C3H response was reversed by alpha-methyl-D-galactoside (alpha MG) but not other sugars, including beta MG. Suppression was associated with a decrease in the level of IL 2, which suggests competition; this decrease was also reversed by alpha MG.

Contrasting modes of action of D-glucose and 3-O-methyl-D-glucose as protectors of the rat pancreatic B-cell against alloxan

Both D-glucose and its nonmetabolized analog 3-O-methyl-D-glucose are known to protect the pancreatic B-cell against the toxic action of alloxan, as if the protective action of hexoses were to involve a membrane-associated glucoreceptor site. In the present study, the protective actions of the two hexoses were found to differ from one another in several respects. Using the process of glucose-stimulated insulin release by rat pancreatic islets as an index of alloxan cytotoxicity, we observed that the protective action of D-glucose was suppressed by D-mannoheptulose and menadione, impaired by NH4Cl, and little affected by aminooxyacetate. These findings and the fact that D-glucose failed to decrease [2-14C]alloxan uptake by the islets suggest that the protective action of D-glucose depends on an increase in the generation rate of reducing equivalents (NADH and NADPH). The latter view is supported by the observation that the protective action of a noncarbohydrate nutrient, 2-ketoisocaproate, was also abolished by menadione. Incidentally, the protective action of 2-ketoisocaproate was apparently a mitochondrial phenomenon, it not being suppressed by aminooxyacetate. In contrast to that of glucose, the protective action of 3-O-methyl-D-glucose was unaffected by D-mannoheptulose, failed to be totally suppressed by menadione, and coincided with a decreased uptake of [2-14C]-alloxan by the islets. It is concluded that the protective action of D-glucose in linked to the metabolism of the sugar in islet cells, whereas that of 3-O-methyl-D-glucose results from inhibition of alloxan uptake. This conclusion reinforces our opinion that the presence in the B-cell of an alleged stereospecific membrane glucoreceptor represents a mythical concept.

Methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside: an inhibitor of sweet taste responses in gerbils

The sugar methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside (DiCl-gal) is a new type of inhibitor of the gerbil's electrophysiological taste response to sucrose or saccharin. Saturated solutions of this compound alone barely stimulate the gerbil's taste nerve. But, when mixed with sucrose or saccharin, DiCl-gal suppresses the gerbil's taste response to these two sweeteners. In contrast, when mixed with sodium chloride or hydrochloric acid, DiCl-gal does not affect the taste responses to these compounds. However, unlike other inhibitors of sweet taste, the DiCl-gal taste suppression is short-lived and occurs only when the inhibitor is combined with the sweetener.

The lack of insulin mimetic or antagonistic effects of methyl-alpha-D-Mannoside in iso-osmolar solutions

Transduction of insulin binding into metabolic control in isolated rat adipocytes apparently requires intact cell surface carbohydrate. The ability of certain lectins and some glycosides to mimic and/or inhibit the actions of insulin had been cited as evidence supporting the hypothesis that a concanavalin A-like binding site on fat cells is crucial to this function. Such a binding site could explain the stimulation by methyl-alpha-D-mannoside of glucose oxidation or its ability to antagonize the effect of insulin on lipolysis. The present study corroborated these effects of methyl-alpha-D-mannoside in hyperosmolar medium, but shows that the effects vanish when osmolarity is maintained within physiological limits. Osmolarity alone could not explain all of the complex effect observed, but it can be concluded that earlier data suggesting methyl-alpha-D-mannoside mimics or antagonizes the actions of insulin cannot be used to support the above hypothesis.

Increased hexose transport in Chinese hamster ovary cells resistant to 3-O-methyl-D-glucose

3-O-Methyl-D-glucose-resistant mutants were selected from Chinese hamster ovary cells after mutagenesis with ethyl methanesulfonate. A mutant, MegR24, was isolated which was significantly more resistant than the parent to 3-O-methylglucose. Uptake of 50 microM D-glucose by metabolizing MegR24 cells was 2- to 3-fold higher than the parental cells in the absence or presence of 100 mM 3-O-methylglucose. A study of transport of D-[3H]glucose in ATP-depleted cells indicated an apparent Km for D-glucose transport that was 3-fold lower for the mutant (2.7 +/- 0.3 mM) than for the parent (8.9 +/- 1.0 mM). The apparent Km for transport of 3-O-methylglucose by the mutant (10.9 +/- 2.4 mM) was almost 2-fold lower than that of the parent (21.4 +/- 4.7 mM). The Vmax values for transport of D-glucose or 3-O-methylglucose by the mutant and parental cell lines were not significantly different. The MegR24 mutant also exhibited enhanced countertransport of D-[3H]glucose following preloading of ATP-depleted cells with 100 mM 3-O-methylglucose. Simple diffusion of hexoses as measured by L-glucose uptake was not altered in the mutant. These results suggest that the MegR24 hexose carrier has an increased affinity for transport of hexoses and that the resistance to the cytotoxic effects of 3-O-methylglucose exhibited by MegR24 is due to its ability to transport D-glucose 2- to 3-fold more efficiently than the parental strain.

Maximizing differences in the concanavalin A-induced blastogenic responses of lymphocytes from breast cancer patients and controls by the use of alpha-methyl-D-mannoside

In an attempt to magnify differences in the immune responses of potentially immunosuppressed cancer patients and normal controls, an assessment was made on the effects of the competitive inhibitor alpha-methyl-D-mannoside on the concanavalin A (Con A)-induced blastogenic responses of lymphocytes from each of these populations. Lymphocytes from breast cancer patients with metastatic disease were significantly deficient in their capability to undergo blast transformation regardless of whether the monosaccharide inhibitor was added to the assay cultures. In contrast, lymphocytes from breast cancer patients who did not display metastatic disease were capable of normal blastogenic responses to Con A. The addition of alpha-methyl-D-mannoside to lymphocyte cultures caused a significantly greater inhibition of the blastogenic responses of these patients' cells as compared to cells of normal controls. Thus the monosaccharide seems to serve as a useful reagent for optimizing differences between lymphocyte blastogenic responses of normal donors and those of immunodepressed donors. The results suggest that lymphocytes from breast cancer patients without clinically evident metastases possess some modification of their cell membrane. One possibility discussed was that the number or distribution of receptors for Con A on the membrane of lymphocytes of these patients is deficient.

Commitment and proliferation kinetics of human lymphocytes stimulated in vitro: effects of alpha-MM addition and suboptimal dose on concanavalin A response

We have examined the effect of alpha-methylmannoside (alpha-MM) addition to concanavalin A (con A)-stimulated peripheral human lymphocytes. With a previously established kinetic model, we have, from the time course of proliferation, extracted the responding clone size, rate of entry of this clone into S phase and the length of the lag period. We have studied the effect of con A dose and time of addition of alpha-MM to optimally stimulated cells on these kinetic parameters. We show that neither a low dose of con A nor an early addition of alpha-MM to optimally stimulated cells results in a change in the responding clone size. This is, all of the potentially cells appears to become "committed" to enter the cell cycle regardless of the presence of alpha-MM early in the culture or in the presence of suboptimal stimulation. However, the rate at which these committed cells enter the first S phase is a function of the dose of con A and time of addition of alpha-MM and varies over a wide range. It is the variation in this parameter that accounts for virtually all of the diminished response previously interpreted as a time-dependent irreversible commitment of mitogen-stimulated cells. The previous work using only fixed time points for measuring thymidine uptake and the concept of commitment must be reevaluated in light of the kinetic evidence presented.

The simultaneous binding of lanthanide and N-acetylglucosamine inhibitors to hen egg-white lysozyme in solution by 1H and 13C nuclear magnetic resonance

Lanthanide ions and the N-acetylglucosamine (GlcNAc) sugars are able to bind simultaneously to hen egg-white lysozyme (EC 3.2.1.17). The present study characterizes the properties of the ternary complexes with lysozyme, which involve up to seven paramagnetic lanthanides and two diamagnetic lanthanides, together with alpha GlcNAc, beta GlcNAc, alpha MeGlcNAc and beta MeGlcNAc. pH titrations and binding titrations of the GlcNAc sugars with lysozyme-La(III) complexes show that the GlcNAc sugars bind to at least two independent sites and that one of them competes with La(III) for binding to lysozyme. Given the known binding site of lanthanides at Asp-52 and Glu-35, the competitive binding site of GlcNAc is identified as subsite E. A simple analysis of the paramagnetic-lanthanide-induced shifts shows that the GlcNAc sugar binds in subsite C, in accordance with crystallographic results [Perkins, Johnson, Machin & Phillips (1979) Biochem. J. 181, 21-36]. This finding was refined by several computer analyses of the lanthanide-induced shifts of 17 proton and carbon resonances of beta MeGlcNAc. Good fits were obtained for all the signals, except for two that were affected by exchange broadening phenomena. No distinction could be made between a fit for a two-position model of Ln(III) binding with axial symmetry to lysozyme, according to the crystallographic result, or a one-position model with axial symmetry where the Ln(III) is positioned mid-way between Asp-52 and Glu-35. Although this work establishes the feasibility of lanthanide shift reagents for study of protein-ligand complexes, further work is required to establish the manner in which lanthanides bind to lysozyme in solution.

Effect of 3-O-methyl-D-glucose on the production of glycosidases by Cryptococcus laurentii and Saccharomyces cerevisiae

3-O-Methyl-D-glucose (3-O-MeGlc) or a mixture of 3-O-MeGlc and glucose stimulate invertase, beta-glucosidase, alpha-glucosidase, and alpha-galactosidase production by Cryptococcus laurentii. They also increase invertase and alpha-glucosidase production by Saccharomyces cerevisiae. The stimulatory effect of 3-O-MeGlc is not caused by competition with glucose for transport nor by a direct action on glycosidases. It is proposed that 3-O-MeGlc acts as a structural rather than as a functional analogue of glucose displacing it from regulatory sites to relieve catabolite repression. Evidence is presented suggesting that intracellular cAMP levels may be related to the effect of 3-O-MeGlc.

Influx of gamma-aminobutyric acid and alpha-aminoisobutyric acid into mouse cerebrum slices incubated in a pyruvate medium with or without added glucose or glucose analogues compared with influx from a glucose medium

Concentrative influx of gamma-aminobutyric acid (GABA) and alpha-amino-isobutyric acid (AIB) into incubated mouse cerebrum slices is decreased when pyruvate is substituted for glucose. Influx of GABA from pyruvate medium is not increased by presence of glucose, 2-deoxy-D-glucose (2-DOG), or 3-O-methyl-D-glucose (3-O-MeG). Influx of AIB is restored to the rate from glucose medium if 2-DOG is present initially, but is not restored if 2-DOG is added with AIB. Influx is not restored if 3-O-MeG is present initially, but is restored if 3-O-MeG is added with AIB. Influx is restored if glucose is present initially or is added with AIB.

The dual effect of alloxan modulated by 3-O-methylglucose or somatostatin on insulin secretion in the isolated perfused rat pancreas

While alloxan treatment stimulated insulin secretion, alloxan pretreatment reduced arginine and glucose-induced insulin secretion in the isolated perfused rat pancreas. The transient insulin secretion by alloxan was inhibited by 3-O-methylglucose and somatostatin. Diminished insulin response to arginine and glucose induced by pretreatment with alloxan was restored by the addition of 3-O-methylglucose, whereas the addition of somatostatin did not improve the impaired insulin secretion. These results indicate that alloxan induced insulin secretion is not due to an uncontrolled leakage, but that the stimulatory and inhibitory action of alloxan on insulin secretion might be initiated by the binding of alloxan to the hexose transport site.

Sugar derivatives and liver mitochondria. I. - Effect of methyl-3,5-di-O-benzyl-2-chloro-2-deoxy-D-arabinofuranoside

Effect of fifteen sugar derivatives on oxygen uptake and oxidative phosphorylation by liver mitochondria were tested. Full details of the possible mechanism of action of methyl-3,5-di-O-benzyl-2-chloro-2-deoxy-D-arabinofuranoside (VI) was presented. This sugar derivative seems to act as inhibitor of the electron transport in the respiratory chain and as an uncoupler.

Prevention of colonization of the urinary tract of mice with Escherichia coli by blocking of bacterial adherence with methyl alpha-D-mannopyranoside

Methyl alpha-D-mannopyranoside (alpha MM), a competitor inhibitor of the binding of mannose by Escherichia coli, was tested for its ability to prevent infection of the urinary tract of mice with infective strains of the organisms. Injection of the bacteria in the presence of the drug resulted in a considerable reduction in the number of bacteriuric mice. In this system alpha MM was inactive against Proteus mirabilis in accordance with its inability to inhibit the adherence of this organism to epithelial cells in vitro, and methyl alpha-D-glucopyranoside proved inactive against both E. coli and P. mirabilis.

Property and activity of mycoloyl esters of methyl glucoside and trehalose. Effect on mitochondrial oxidative phosphorylation related to organization of suspensions and to acyl-chain structures

Methyl alpha-D-glucoside and alpha, alpha'-D-trehalose acylated on their primary hydroxyl group by alpha-alkyl-beta-hydroxy acids (mycolic acids) with 18, 32 and more than 80 carbon atoms were studied. These cord factors and analogues when dispersed in water gave hydrated and organized phases which bore resemblances and differences to phospholipid liposomes. Phase transition temperature was determined by fluorescence for the C32 derivatives and by differential scanning calorimetry for the C80 derivatives. A narrow temperature interval between the gel and the fluid states was observed, indicating that this transition was a strongly cooperative phenomenon. The activity on mitochondria of these diacyl trehaloses was studied with succinate as substrate. The fluid suspensions were more active than the rigid ones. There was no influence of the relative configuration of the mycoloyl residue. Acyl chains with 18, 32 and more than 80 carbon atoms had rather similar activities on phosphorylation, but differences appeared when considering effects on respiration. Electron microscopy suggested that cord factor weakened the peripheral part of the inner membrane, but cristae looked unchanged. These observations, together with the results of our previous monolayer studies of these glycolipids, led us to propose a model for interaction of cord factor with mitochondria.

Reduction of streptozotocin toxicity by 3-O-methyl-D-glucose with enhancement of antitumor activity in murine L1210 leukemia

3-O-Methyl-D-glucose (3-OMG), a nontoxic nonmetabolizable derivative of glucose, is effective in reducing the toxicity of streptozotocin (SZ). In mice the administration of 3-OMG prior to SZ increased the dose that killed 50% of the animals from 240 to 340 mg/kg. Furthermore, the combination of 3-OMG plus nicotinamide (also effective in reducing SZ toxicity) increased the dose that killed 50% of the animals to 540 mg/kg. In L1210 leukemic mice treated with SZ, there was a 2-fold increase in the median survival of animals pretreated with 3-OMG and a 3-fold increase in that of animals pretreated with the combination of 3-OMG and nicotinamide. Neither 3-OMG nor nicotinamide alone enhanced the survival of the leukemic mice. Pretreatment of normal mice with 3-OMG partially prevented the expected fall in hepatic nicotinamide adenine dinucleotide content. This study suggests that 3-OMG, by protecting normal tissue, will permit the administration of larger therapeutic doses of SZ in leukemic L1210 mice. The protective effect of 3-OMG against SZ toxicity appears to be partially mediated through conservation of the nicotinamide adenine dinucleotide content in the tissue.

Glucose and 3-O-methylglucose protection against alloxan poisoning of pancreatic alpha and beta cells

Alloxan infused into the isolated perfused rat pancreas caused transient insulin secretion release. Alloxan poisoning also prevented subsequent induction of glucose-mediated unsulin release and also prevented the inhibition of glucagon release by glucose. Glucose or 3-O-methylglucose infused simultaneously with alloxan protected the alpha- and beta-cell, allowing subsequent glucose inhibition of glucagon secretion and stimulation of insulin release. The above alloxan effects were dose-related, the alpha-cell being one fourth as sensitive to alloxan as the beta-cell. The data indicate that (1) alloxan and glucose suppression of amino-acid-stimulated glucagon secretion is independent of concomitant insulin secretion; (2) alloxan, like glucose, affects alpha-and beta-cells directly, stimulating the beta-cell and inhibiting the alpha-cell; and (3) alloxan acts on a glucoreceptor system with comparable physicochemical characteristics common to both cell types.

Effects of iodoacetate, mannoheptulose and 3-O-methyl glucose on the secretory function and metabolism of isolated pancreatic islets

The ability of iodoacetate, mannoheptulose, and 3-O-methyl glucose to alter islet cell metabolism and glucose-stimulated insulin secretion was examined. A method for the sequential analysis of the releasing and fuel function of glucose in isolated islets was applied. Insulin release was measured by radioimmunoassay and the metabolism of glucose by determining the rate of tritiated water production from [5-3H]glucose and lactate accumulation. It was found that iodoacetate, in the range of 0.2-1.0 mM, inhibited the metabolism of glucose linearly while release was not blocked until metabolism was reduced by 30-40%. The KI for both processes, release and metabolism, was the same. Pyruvate did not protect against or reverse the effects of iodoacetate. Mannoheptulose inhibited both release and metabolism half-maximally at about 5 mM when 27.5 mM glucose was used as the stimulatory agent. A mannoheptulose-resistant component of glucose metabolism, amounting to 30% of the maximal rate was observed. 3-O-Methyl glucose had no effect on insulin release but reduced glucose utilization and lactate production from low glucose. The results are discussed in light of the two prevailing hypotheses explaining glucose induced insulin release, i.e., the receptor and the metabolism hypotheses.

Studies on 6C3HED murine ascites tumor cell receptors for mannosyl-binding lectins

We have investigated the receptor site activity present on 6C3HED tumor cells for concanavalin A, fava, lentil and pea lectins. The binding of the tritiated lectins to the tumor cells was inhibited by methyl-alpha-D-mannoside but not by D-galactose. The number of binding sites for the lectins was 3.5-10(6)/cell for concanavalin A, 3.3-10(6)/cell for fava, 3.6-10(6)/cell for lentil and 4.8-10(6)/cell for pea. The apparent association constants were 3.6 and 1.3 muM-1 for concanavalin A, 3.9 muM-1 for fava, 4.2 muM-1 for lentil and 4.6 and 0.6 muM-1 for pea. Competitive inhibition studies showed that lentil was a good inhibitor of pea binding; concanavalin A was a poor inhibitor of pea binding; and fava was a better inhibitor than concanavalin A but not as good as lentil. Reciprocal inhibition experiments indicated that concanavalin A and pea may bind to different receptors as well as to common receptors. This was also indicated by the observation that trypsin or protease treatment of the cells decreased the binding of pea lectin by 20-40 percent whereas concanavalin A binding was unaffected.

Studies on streptozotocin diabetes

Both alloxan and streptozotocin produce beta-cell necrosis in the rat. Previous studies have shown protection against alloxan toxicity by D-glucose, D-mannose, and the nonmetabolized analogue 3-0-methyl-D-glucose and removal of this protective effect by D-mannoheptulose. The effect of several agents (i.v. infusion) against the beta-cell toxic effect of streptozotocin (60 mg./kg. i.v. in 24-hour-fasted 200-gm. male rats) was studied. Protection was determined by plasma glucose concentrations 24 and 48 hours later and, in certain experiments, by histologic examination of the islets. D-glucose and D-mannose provided no protection. Similarly, D-galactose, D-fructose, alpha-methyl-D-glucoside, D-L-glyceraldehyde, D-xylose, and D-glucosamine had no effect. However, 3-0-methyl-D-glucose administered immediately before streptozotocin resulted in progressive inhibition of beta-cell toxicity with complete protection at 0.83 mMoles per rat. The protective effect of 3-0-methyl-D-glucose was not altered by mannoheptulose. 2-Deoxy-D-glucose, which has no effect against alloxan, provided nearly complete protection against streptozotocin at 2.2 mMoles per rat. The effects of 3-0-methyl-D-glucose and 2-deoxy-D-glucose were additive and were not altered by glucose. Furthermore, the 3-0-methyl-D-glucose as well as 2-deoxy-D-glucose protective effects were still present, albeit attenuated, when these agents were given following the administration of streptozotocin. This is in contrast to alloxan, against which 3-0-methyl-D-glucose provides protection only when given before alloxan. 3-0-Methyl-D-glucose is the only carbohydrate protective against both streptozotocin and alloxan in the rat. However, several silent differences seem to exist between the mechanisms of beta-cytotoxic effects of these two diabetogenic compounds.

Inhibition of the in vivo effects of concanavalin-A on mammalian epidermis by alpha-methyl-D-glucopyranoside

Concanavalin-A (Con-A) injected intradermally into newborn rats produces inhibition of granular-cell formation, accumulation of spinous cells, glycogen deposition, and a decrease followed by an increase in the number of basal cells in DNA synthesis. These changes were maximal with a dose of 0.1 mg Con-A, although 0.005, 0.01, and 0.05 mg caused some epidermal changes. The Con-A effects were partially blocked when 0.1 ml of 0.3 or 0.1 M alpha-methyl-D-glucopyranoside (alphaMG) solution was injected 2 hr after 0.1 mg Con-A and completely inhibited by injection of 0.1 ml of 3.0 M alphaMG solution. The inhibitory effects were not seen after injection of 0.1 ml of 3.0 M N-acetyl-galactosamine saline solution, or 0.1 ml normal saline. Injection of alphaMG alone did not cause any changes in epidermal cells. These results indicate that specific sugar inhibits Con-A effects on mammalian epidermis in vivo.

Renal proximal tubular buffer-(glycodiazine) transport. Inhomogeneity of local transport rate, dependence on sodium, effect of inhibitors and chronic adaptation

Using the stop flow microperfusion technique with simultaneous capillary perfusion the secretory rate of H+ ions in the proximal tubule was evaluated by measuring the level flow reabsorption as well as the static head concentration difference of 3H labeled glycodiazine. At ambient glycodiazine concentration of 21 mmol/l the level flow reabsorption is in the same range as that of bicarbonate. In the early proximal loops the reabsorption is 20% greater than in the late proximal loops. The carbonic anhydrase inhibitors acetazolamide and 3,4-methylene-dioxyphenyl-sulfonamide (both 10(-4) M) as well as furosemide (10 (-3) M) inhibit the glycodiazine reabsorption 43%, 27% and 22% respectively. Thiocyanate (2-10(-2) M), however, exerted only an insignificant inhibition (12%). When Na+ in the ambient perfusion solutions was replaced by Li+ or choline+ the glycodiazine transport was strongly reduced. Ouabain (5-10(-2) M) inhibited too, but amiloride (10(-3) M) had no effect on glycodiazine transport. The glycodiazine transport was 28% reduced in metabolic alkalosis and to a smaller although significant extent (17%) in metabolic acidosis; it was unchanged in chronic hypercapnia. In chronic K+ depletion the glycodiazine reabsorption was accelerated by 12% only in the early proximal loops. Chronic parathyroidectomy as well as acute substitution with parathyroid hormone had no effect on the glycodiazine absorption. The main conclusions are: Proximal H+ transport proceeds with suitable buffers. Although independent of HCO3- and carbonic anhydrase, it could be partially inhibited by CA inhibitors. H+ transport is supposed to proceed as countertransport with Na+ ions. In chronic alkalosis the H+ transport is reduced.