Glycosylation characteristics of the mouse liver lactogenic receptor

The structural characteristics and glycosylation properties of the lactogenic receptor were examined in 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS)-solubilized plasma membranes from female mouse liver. The specific binding of the radioiodinated human growth hormone [( 125I]hGH) was displaced with an equivalent potency by both hGH and prolactin. After a mild neuraminidase treatment, this binding was increased by 40%, as a result of an increase in receptor affinity. Affinity chromatography on immobilized lectins revealed that the [125I]hGH-receptor complexes were specifically retained and eluted from ricin lectin-agarose, concanavalin A and lentil lectin, indicating the presence of N-linked glycans. Covalent cross-linking of solubilized [125I]hGH-receptor complexes with disuccinimidyl suberate, followed by analysis by sodium dodecyl sulfate-gel electrophoresis (SDS-PAGE) under reducing conditions, and autoradiography resulted in the appearance of two bands with apparent Mr approximately 62,000 and approximately 100,000. The labelling of these bands was prevented by unlabelled hGH or ovine prolactin (oPrl) but not by bovine growth hormone (bGH). Neuraminidase treatment of the two receptor forms resulted in increased electrophoretic mobility which was inhibited by simultaneous addition of sialyl-lactose, a neuraminidase substrate. The both cross-linked forms were unaffected by endoglycosidase H, while endoglycosidase F decreased the molecular weight of each of the forms by about 8000 Da, yielding bands at Mr approximately 54,000 and approximately 92,000. In conclusion, taking into account that hGH is a Mr 22,000 polypeptide, the two forms of the receptor correspond to glycoproteins of Mr approximately 40,000 and approximately 78,000, respectively. They contain polypeptide backbones of Mr approximately 32,000 and approximately 70,000, and complex N-linked oligosaccharide chains with terminal sialic acid residues which could be involved in receptor binding affinity.

Tyrosine-kinase defect of the insulin receptor in cultured fibroblasts from patients with lipoatropic diabetes

Postbinding defects in insulin action were described previously in cultured fibroblasts from six patients with lipoatropic diabetes. To define the contribution of the insulin receptor tyrosine kinase in these defects, we studied autophosphorylation and kinase activity of lectin purified receptors from these six patients and six normal cell lines. The patients' insulin receptors, prepared by precipitation with polyethylene glycol, had normal insulin binding characteristics and autophosphorylation properties, but a 56% decrease in the tyrosine kinase activity toward an exogenous substrate. To identify more subtle qualitative defects in autophosphorylation, insulin receptors were sequentially immunoprecipitated and analyzed for their phosphoaminoacid content. The phosphorylated receptors precipitated with an antiphosphotyrosine antibody contained labeled phosphotyrosine, whereas those in the supernatant, when further precipitated with an antireceptor antibody, contained only phosphoserine. Under these conditions, the insulin-stimulated autophosphorylation of tyrosine was significantly decreased by 54% in the patient receptors compared to normal subjects' receptors. In addition, insulin-like growth factor-I stimulation of autophosphorylation of its receptor was reduced by 59% in the patients' cells compared to those from normal subjects. We conclude that fibroblasts from patients with lipoatropic diabetes have defects in the tyrosine kinase activity of their insulin and their insulin-like growth factor-I receptors that might give rise to the in vitro hormone resistance and be related to the in vivo hormone resistance that occurs in these patients.

Insulin action is mimicked by polyclonal antireceptor antibodies that activate the insulin receptor tyrosine kinase

The insulin-like properties of anti-insulin receptor antibodies (P95 Ab) that have been characterized as being directed against the receptor beta-subunit, were studied as probes to assess the interrelationship between insulin action and receptor phosphorylation. When tested on intact cells, P95 Ab mimicked insulin effects. On isolated fat cells, they stimulated 2-deoxyglucose (2-DG) transport and lipogenesis and the P95 antibody maximal effects (173 and 232% of the control values, respectively) represented about 50% of the maximal effects elicited by insulin (317 and 475% of the control values). On cultured Zajdela hepatoma cells (ZHC cells), P95 Ab also mimicked insulin action on the incorporation of [U-14C]glucose into glycogen (158 and 207% of the control value for antibody- and insulin-treated cells, respectively). In all cases the antibody effects were dose-dependent, specific and, when maximal, were not additive with those elicited by insulin. When tested in a cell-free system, P95 Ab faithfully reproduced insulin action on the phosphorylation of the receptor beta-subunit. The maximal antibody and insulin effects (317 and 328% of the control value, respectively) were not additive. P95 Ab were also equally potent as insulin to stimulate the receptor-mediated phosphorylation of an exogenous substrate (365 and 379% of the control value in P95 antibody- and insulin-treated receptors, respectively). As well, P95 Ab proved as able as insulin in stimulating the tyrosine kinase activity of the receptor (89% of the hormone effect) when the activation was carried out in vivo. Taken together, these results are consistent with a role for the kinase activity of the insulin receptor in mediating the action of insulin.

Purification and characterization of a galactoside-binding lectin from human brain

A beta-galactoside-binding hemagglutinin was detected in soluble extracts of human brain. This soluble lectin was purified to homogeneity by affinity column chromatography on lactose coupled to divinylsulfone-activated agarose. The purified lectin had an isoelectric point of 3.9 and its subunit molecular mass estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate was 14,500. Human brain lectin was not a glycoprotein and its amino acid composition was characterized by a high content of serine, glutamic acid, and glycine, and a low content of methionine and cysteine. The most potent saccharide inhibitors tested were thiodigalactoside, lactose, and p-nitrophenyl-beta-D-galactoside. An antibody was raised to the pure lectin. Immunological relationships were found between the brain lectin and several other soluble lectins of various vertebrate origins.

Immunohistochemical localization of a beta-galactoside-binding lectin in rat central nervous system. II. Light- and electron-microscopical studies in developing cerebellum

An endogenous brain lectin exhibiting beta-galactoside specificity (RBL-16) was localized during postnatal cerebellum development both at the light- and electron-microscopical level. The lectin was widely distributed in neurons, astroglial and perivascular cells. Its levels were nearly constant during development in the two latter cell types. The lectin was developmentally regulated with a transient accumulation in Purkinje dendritic spines between the 10th- and 13th day, then it decreased until adult age. From electron-microscopical observations, it could be concluded that, in Purkinje cells, the lectin remained in the intracellular compartment, in dendrites and cell bodies. It was never externalized in the region where synaptogenesis takes place. A role in the intracellular transport of molecules should be expected from such a localization. The lectin was also transiently found on the surface of postmitotic neuroblasts in the external germinative layer and on the parallel fibers of the upper part of the molecular layer. However, it was not expressed inside neuroblasts. This suggests that part of the lectin found on the surface of neuroblasts originates from heavily stained astrocytes which could secrete it. RBL-16 could be making bridges between neuroblasts in the premigratory zone and between growing axons. A role in transient neuroblast adhesion in the external germinative layer and in parallel fiber fasciculation is expected from such a localization.

Immunohistochemical localization of a beta-galactoside-binding lectin in rat central nervous system. I. Light- and electron-microscopical studies on developing cerebral cortex and corpus callosum

From a lectin isolated from human brain (HBL-14), that specifically binds beta-galactosides, a polyclonal antiserum was raised that also recognizes a similar rat brain lectin (RBL-16). These antibodies allowed the immunocytochemical localization of the lectin during rat brain development by optical and electron microscopy. The presence of RBL-16, first detected at embryonic day 15, was specially increased from postnatal day 1 to 10. Its level decreased thereafter but it could still be detected in adult rat brain. The lectin, predominantly neuronal until postnatal day 13, was also present in astrocytes and perivascular cells where no developmental regulation was observed in contrast to neurons. Electron microscopy showed that the lectin was transiently expressed in the axoplasm of almost all neurons in layer I around the birth date, after which it remained inside neurons, including cell bodies and dendrites, in all examined regions. The lectin was clearly localized in postsynaptic structures. This beta-galactoside-specific lectin may be involved in synaptogenesis and neurite fasciculation as well as in intracellular traffic as discussed.

Genetic convergence during serial in vitro passage of a polyclonal squamous cell carcinoma

A cell line was established from an in situ squamous cell carcinoma of the skin (Bowen's disease), and its in vitro karyotypic evolution was cytogenetically analyzed. Initially, considerable genetic heterogeneity was evident. Nine cytogenetically abnormal clones, eight of which were apparently unrelated, were found among the 83 metaphases analyzed from the primary culture and the first passage. With increasing time in culture this complexity was reduced, so that a single clone dominated passages 7-11. The clone that emerged from this genetic convergence had a t(12;17)(p13;q21) as the sole abnormality. Our findings indicate that the cytogenetic multiclonality that has been repeatedly detected in short-term cultures of squamous cell carcinomas is not caused by the in vitro conditions. Instead, the principles of Darwinian selection apply: the altered, but stable, selection pressure facing a newly established and initially multiclonal cell line will lead to a reduction of genetic heterogeneity until the one clone that now has the proliferative advantage outgrows the other subpopulations.

Effect of protein kinase C activation and depletion on insulin stimulation of glycogen synthesis in cultured hepatoma cells

Insulin stimulation of glycogen synthesis was nearly abolished in hepatoma cells shortly treated with 4 beta-phorbol 12 beta-myristate, 13 alpha-acetate (protein kinase C activation) but remained unmodified in cells chronically treated with the phorbol ester (protein kinase C depletion). Thus, although exogenous activation of protein kinase C results in an inhibition of insulin action, protein kinase C depletion has no influence on this process. The results suggest that, in hepatoma cells, no endogenous activation of protein kinase C may occur in response to the signal triggered by insulin.

Characterization of the radioiodinated analogue of SCH 23390: in vitro and in vivo D-1 dopamine receptor binding studies

A new radioiodinated molecule, 125I-SCH 38840 (previously referred to as 125I-SCH 23982), has been recently reported to be a D-1 dopamine receptor ligand. The current study confirms and expands the characterization of both the radiolabeled and unlabeled forms of this compound, as well as describing the development of an in vivo D-1 receptor binding assay utilizing the 125I-SCH 38840. The binding of 125I-SCH 38840 to rat striatal membranes, in vitro, was saturable and exhibited a KD of 1.47 nM. Competition studies using 125I-SCH 38840 exhibited a pharmacological profile consistent with the proposal that 125I-SCH 38840 was binding to the D-1 receptor. Further studies with the unlabeled SCH 38840 demonstrated that it inhibited dopamine-stimulated adenylate cyclase with a KI of 66.1 nM, indicating that SCH 38840 was acting as a D-1 antagonist. Behavioral studies demonstrated that SCH 38840 (MED = 1.0 mg/kg, s.c.) blocked conditioned avoidance responding in rats, a measurement considered predictive of anti-psychotic activity in man. In vivo binding of 125I-SCH 38840 to rat striatum following s.c. administration was specific. Peak striatal levels were observed 1 h after injection, with measurable binding observed out to 8 h post-treatment. The displacement of the in vivo binding by unlabeled standards again suggested a D-1 selective interaction. The half-life of the in vivo binding of 125I-SCH 38840 was approximately 1.25 h, and was nearly equivalent to the half-life of the anti-CAR activity of unlabeled SCH 38840. These results clearly demonstrate the D-1 nature of SCH 38840's behavioral activity and strengthen the anti-psychotic potential of a D-1 antagonist.

Purification and some characteristics of a beta-galactoside binding soluble lectin from amphibian ovary

Soluble extracts of Bufo ovaries agglutinate sialidase-treated rabbit erythrocytes. Unlike other amphibian lectins this agglutination activity does not require the presence of calcium ions. It is specifically inhibited by D-galactose and its derivatives. Thiodi-D-galactoside is the most potent saccharide inhibitor followed by lactose and methyl-beta-D-galactoside, respectively. D-Fucose, D-glucose and D-mannose do not inhibit the activity at concentrations at or above 100 mM. The lectin has been purified 500-fold to apparent homogeneity from the ovaries by salt extraction and affinity chromatography on lactose-aminophenyl-agarose, with a yield of about 0.2%. The molecular mass determined by gel filtration under native conditions was 30 kDa; polyacrylamide gel electrophoresis in SDS gave a molecular mass of 15 kDa, suggesting that the lectin is a dimer. The lectin has an isoelectric point of 40 and contains a high proportion of acidic amino acids.

Brain lectin-mediated agglutinability of dissociated cells from embryonic and postnatal mouse brain

Brain extracts contain a soluble lectin which enables the agglutination of dissociated mouse brain cells via saccharidic receptors. The ability of the brain cells to be agglutinated depends on their stage of development in vivo. Furthermore, after birth, the mechanism of the lectin-promoted agglutination is complicated by the appearance of a self-aggregation of the dissociated cells. Lactose and galactosides are inhibitors of lectin-mediated agglutination as well as of the dissociated cells' self-aggregation.

Purification and characterization of a beta-galactoside-binding soluble lectin from rat and bovine brain

A beta-galactoside-binding activity has been detected in mammalian brain extracts using a hemagglutination test and a nerve cell aggregation assay. Inhibition studies suggested the involvement of lectin-carbohydrate interactions in these processes. In an attempt to explore further the biological role of brain lectins, the beta-galactoside-binding activity has been purified to apparent homogeneity from bovine and rat brain by salt extraction of the brain tissue and affinity chromatography on asialofetuin-agarose. The molecular weights determined by gel filtration, under native conditions on Ultrogel AcA-34, were 30,000 for the bovine brain lectin and 32,000 for the rat brain lectin; polyacrylamide gel electrophoresis in SDS gave molecular weights of 15,000 and 16,000, respectively, suggesting that the two brain lectins are dimers. Both lectins have an isoelectric point of 3.9. Amino acid composition data indicate that both lectins contain high proportions of glycine and acidic amino acids. The lectins are specific for beta-D-galactosides and related sugars and the configuration of carbon atoms 1, 2 and 4 seems of primary importance. Moreover, the nerve cell aggregation-promoting activity of the purified lectin is 300-fold that of the crude extracts.

Decreased insulin responsiveness in fat cells rendered protein kinase C-deficient by a treatment with a phorbol ester

Insulin stimulation of 2-deoxyglucose transport and lipogenesis from glucose was examined in fat cells in which protein kinase C had been down-modulated by a 3 h pretreatment with 5 X 10(-7) M 4 beta-phorbol 12 beta-myristate, 13 alpha-acetate (PMA). As compared to control fat cells, the down-modulated cells exhibited a 55-65% decrease in insulin responsiveness with no change in either the hormone sensitivity or the insulin receptor affinity. The present study shows that fat cells made protein kinase C-deficient by chronic treatment with PMA exhibit an insulin-resistant state, distal to the initial step of hormone binding.

The Kapandji technique and its evolution in the treatment of fractures of the distal end of the radius. Report on a series of 159 cases

The authors analyse the results of treatment of 159 fractures of the distal end of the radius by the "Kapandji Technique". Of these 159 fractures, 129 were extra-articular, 27 intra-articular and 3 fractures affected both the two bones of the forearm. The technique should be applied strictly, with primary reduction and direct control of the tendinous and nervous elements through the incisions. A third pin is sometimes necessary. A 5 years postoperative period is sufficient to get a meaningful analysis of the results which were very good or good in 93% of our cases. The only real problem was anterior over-reduction due to progressive secondary displacement which necessitated regular postoperative follow-up.

Alteration by concanavalin A of the slow dissociable component in the human growth hormone-receptor interaction

In mice liver plasma membranes (PM), the binding affinity of receptors for [125I] human growth hormone (hGH) was dependent on the association time: after 18 hours, a high affinity receptor form with KA = 6.8 X 10(9) M-1 accumulated and, as compared to after 1 hour, an increase up to 88%, in a slow dissociating component was observed. Preincubation of PM with concanavalin A (Con A) or other lectins from Lens culinaris (LCA), Ricinus communis (RCA I), Wheat germ agglutinin (WGA) specifically inhibited the binding of hGH to receptors by 54, 28, 50 and 25%, respectively. Furthermore, PM pretreatment with Con A concomitantly increased the rate of dissociation of the hormone-receptor (H-R) complex to 92 or 65% after association for 1 or 18 hours. These Con A-induced alterations resulted from a reduced fraction of the slow dissociable component together with an increased rate constant. The treatment of PM with Con A subsequent to incubation with the hormone did not decrease hormone binding but caused the conversion of the class of hGH receptors exhibiting fast dissociation kinetics towards a form exhibiting slow ones. These data strongly suggest a role for glycoproteins of the N-acetyllactosaminic type in the affinity state of liver membrane hGH receptors.

Biochemical markers in the assessment of protein-calorie malnutrition in premature neonates

We studied 135 premature newborns of 26 to 36 weeks gestation, divided into three groups: the control group, 66 premature infants with uncomplicated course; 51 premature neonates with appropriate birth weight for gestational age (AGA), who suffered from clinical problems that delayed oral feeding; and 18 premature infants with small birth weight for gestational age (SGA). When neonates of the same postnatal age were compared, prealbumin concentrations were the lowest in the SGA group at the third and fourth postnatal week. Although the AGA group had the most infants with serious illnesses and the lowest protein-calorie intakes, their prealbumin concentrations did not differ significantly from those of the control group. But when the infants of each group were subdivided on the basis of intakes and weight gain regardless of postnatal age, those with greater intakes showed significantly higher prealbumin values; however, in all groups, the infants with higher intakes were also significantly older. Total proteins and albumin showed similar changes in all groups. Prealbumin concentrations showed great interindividual variability in infants of the same postnatal age. We conclude that prealbumin, albumin, and serum total proteins are not sufficiently sensitive biochemical markers to assess alterations of the nutritional status of premature infants.

Biochemical markers in the assessment of protein-calorie malnutrition in premature neonates

We studied 135 premature newborns of 26 to 36 weeks gestation, divided into three groups: the control group, 66 premature infants with uncomplicated course; 51 premature neonates with appropriate birth weight for gestational age (AGA), who suffered from clinical problems that delayed oral feeding; and 18 premature infants with small birth weight for gestational age (SGA). When neonates of the same postnatal age were compared, prealbumin concentrations were the lowest in the SGA group at the third and fourth postnatal week. Although the AGA group had the most infants with serious illnesses and the lowest protein-calorie intakes, their prealbumin concentrations did not differ significantly from those of the control group. But when the infants of each group were subdivided on the basis of intakes and weight gain regardless of postnatal age, those with greater intakes showed significantly higher prealbumin values; however, in all groups, the infants with higher intakes were also significantly older. Total proteins and albumin showed similar changes in all groups. Prealbumin concentrations showed great interindividual variability in infants of the same postnatal age. We conclude that prealbumin, albumin, and serum total proteins are not sufficiently sensitive biochemical markers to assess alterations of the nutritional status of premature infants.

Insulin stimulation of glucose metabolism in rat adipocytes: possible implication of protein kinase C

The hypothesis that insulin stimulation of glucose and lipid metabolism in rat adipocytes may involve the activation of protein kinase C was evaluated. 4 beta-Phorbol 12 beta-myristate, 13 alpha-acetate (PMA, 0.1-1000 ng/ml), a potent tumor promoter acting as a substitute for diacylglycerol to activate protein kinase C, stimulated 2-deoxyglucose transport in a time- and dose-dependent manner, without affecting passive glucose diffusion. PMA (0.1-1000 ng/ml) also elicited a dose-dependent activation of lipogenesis from [3-3H] glucose. Maximal PMA effects (100 ng/ml) on both processes were 60% of insulin maximal effects. In contrast, PMA (1-1000 ng/ml) failed to mimic the ability of insulin to stimulate lipogenesis from [3H]acetate. 4 beta-Phorbol 12,13 dibutyrate, mezerein, 1-oleyl-2-acetyl-glycerol, 1,2 diolein, known as protein kinase C activators, also markedly stimulated glucose metabolism whereas 4 alpha-phorbol 12,13 didecanoate and 4 beta-phorbol 13-monoacetate, shown not to activate protein kinase C, were ineffective. Mellitin, a cytotoxin-inhibiting protein kinase C, markedly decreased both PMA and insulin stimulation of glucose metabolism. PMA decreased insulin submaximal effects on 2-deoxyglucose transport without inhibiting insulin binding. Maximal PMA and insulin effects on 2-deoxyglucose transport and lipogenesis from [3-3H]glucose were not additive. Both PMA and insulin activated each metabolic process in a calcium-dependent manner. PMA, like insulin, no longer stimulated 2-deoxyglucose transport in fat cells treated with 2,4-dinitrophenol. These data show that PMA exhibited specific insulin-like properties on glucose metabolism in fat cells, without any effect on lipid synthesis from acetate. They indicate that PMA and insulin bioeffects may share a common step implicating a calcium- and energy-dependent process, distal to the initial insulin binding event. Our results suggest that protein kinase C may play a role in insulin regulation of glucose metabolism.

Effect of Glomus intraradices on infection by Fusarium oxysporum f.sp. radicis-lycopersici in tomatoes over a 12-week period

The interaction between Glomus intraradices Schenck & Smith, a vesicular–arbuscular mycorrhizal fungus, and Fusarium oxysporum Schlecht f.sp. radicis-lycopersici Jarvis & Shoemaker and its effect on tomato plants were investigated over a 12-week period. The root colonization by Glomus was not affected by the presence of Fusarium. The number of Fusarium propagules was consistently lower when the plants were inoculated with Glomus. The presence of Glomus decreased root necrosis caused by Fusarium in weeks 5, 11, and 12, but no significant effect was observed for the other 9 weeks. The results obtained at any observation time for the endomycorrhizal colonization and the Fusarium population, but not for the percent of root necrosis evaluation, were consistent throughout the 12-week experiment. It is concluded that the parameters used to study the interaction between a vesicular–arbuscular mycorrhizal fungus, a fungal root pathogen, and a host plant must be measured at different times after inoculation with the pathogen to make sure that observations are representative of the interaction under study.

Investigation on the occurrence of soluble lectins in mammalian nervous tissue extracts

Five brain or retina crude extracts obtained from adult mammalians and nine fractions of brain extracts prepared by chromatography were screened for their lectin activities. All crude extracts and several fractions contained agglutinins reacting with neuraminidase-treated rabbit red blood cells. Hemagglutination activity varied widely with the method of preparation of the extracts. Hemagglutination inhibition tests were carried out to look for possible differences in the specificities of the agglutinins. All were found to be D-galactosyl specific. Each crude extract was found to contain a second lectin activity, which was detected using ethanol-treated rabbit erythrocytes known to react with heparin-binding lectins. Hemagglutination and inhibition studies showed that they completely differ from the galactoside-binding lectins detected previously. The possible functions of these lectins are discussed.

Difference in blister fluid penetration after single and multiple doses of ceftriaxone

Plasma and suction skin blister fluid concentrations of ceftriaxone were studied in 12 subjects after intravenous administration of 1 g of ceftriaxone every 12 h (q12h) and 2 g every 24 h (q24h) after single and multiple doses. Ceftriaxone concentrations were determined by high-pressure liquid chromatography. Mean peak plasma concentrations (at the end of the 5-min infusion) were 254.0 and 374.8 micrograms/ml after administration of 1 g q12h after single and multiple doses, respectively. Similarly, with 2 g q24h, maximum levels were 409.6 and 443.5 micrograms/ml. Forty-eight hours after the last dose of ceftriaxone, plasma concentrations were still detectable: 1.2 micrograms/ml after 1 g q12h and 3.0 micrograms/ml after 2 g q24h. Higher ceftriaxone concentrations were observed in blister fluid after multiple doses than after a single dose. Peak concentrations almost doubled in the blister fluid after multiple doses: 36.0 versus 67.0 micrograms/ml and 38.6 versus 68.9 micrograms/ml for 1 g q12h and 2 g q24h, respectively. Elimination half-life of ceftriaxone in the blister (8.3 and 11.5 h) was longer than plasma half-life (6.3 h). With the area under the concentration-time curve ratio, a 113% increase in tissue penetration was observed after multiple doses for the 1 g q12h regimen. The free plasma and blister fluid ceftriaxone concentrations observed at the end of the dosing interval of the 2 g q24h regimen were higher than the MIC for 90% of the susceptible microorganisms and justified the once-a-day use of ceftriaxone.

[Quantitative measurement of lectin activities using an autoanalyser]

Today, an increasing number of lectins are available for a diagnostical purpose. Using an autoanalyser, it is possible to study and to measure the agglutination of red blood cells, one of their main properties.

Further evidence for the involvement of a membrane proteolytic step in insulin action

The hypothesis that insulin action involves a membrane proteolytic step was further explored, by using isolated rat adipocytes and liver plasma membranes. (1) The maximal insulin stimulation of 2-deoxyglucose transport and lipogenesis in fat-cells was selectively inhibited (73-88%) by N alpha-p-tosyl-L-lysine chloromethyl ketone (Tos-Lys-CH2Cl; active-site inhibitor of trypsin; 30-125 microM), p-nitrophenyl p'-guanidinobenzoate (active-site inhibitor of serine proteinases; 30-125 microM) and p-tosyl-L-arginine methyl ester (arginine ester substrate analogue of proteinases; 1-2 mM), under conditions where neither the basal rate of each metabolic process nor insulin binding nor cellular ATP content were affected. In contrast, N-acetyl-L-alanyl-L-alanyl-L-alanine methyl ester (alanine ester substrate analogue of proteinases; 1-2 mM) was ineffective. (2) Endoproteinase Arg-C (0.25-40 micrograms/ml) exerted dose-dependent insulin-like effects on both 2-deoxyglucose transport and lipogenesis in fat-cells, whereas endoproteinase Lys-C (5-100 micrograms/ml) was ineffective. The maximal activation by endoproteinase Arg-C of both processes (200 and 177% of control values respectively) was shown to occur under conditions where membrane integrity (assessed by measurement of lactate dehydrogenase leakage and passive glucose diffusion) was preserved. This effect was inhibited by Tos-Lys-CH2Cl (125 microM) and was not additive with the maximal insulin effect. (3) Insulin (1-100 ng/ml) produced a dose-dependent increase in the trichloroacetic acid-soluble 125I radioactivity released after a 30 min incubation at 37 degrees C of 125I-labelled liver plasma membranes, but was ineffective on 125I-labelled bovine serum albumin. Insulin effects on both radio-labelled proteins were reproduced by wheat-germ agglutinin (20 micrograms/ml), an insulin mimicker shown to act through the insulin receptor. These data provide further evidence for the hypothesis that insulin bioeffects involve the activation of a membrane serine proteinase with arginine specificity.