Oligoclonal beta-galactoside-specific gamma immunoglobulins allow the immunocytochemical detection of cellular antigenic determinants expressed in mouse brain after surgical injury

Histological brain sections were probed with human oligoclonal lectin-like IgGs (L-IgG) purified from normal serum. In intact brain, antigenic determinants for these IgG were restricted to some blood vessel endothelial cells. By contrast, during the inflammatory reaction following a surgical injury, these determinants were detected at the cell surface of different cell types, within and near the lesion site. The cells reacting with L-IgG consisted of endothelial cell, mature astrocytes, activated microglial and ependymal cells.

Networking guru cherishes 'the links'. Interview by Damon Braly

"The links" takes on several meanings to avid sportsfan and networking guru Mark Caron, director of networking and personal computing for Healthsource, Inc., Hookset, N.H. Caron is attempting to lead the way among integrated healthcare delivery networks by setting up a client/server architecture, videoconferencing and Internet connections between Healthsource sites.

Purification and characterization of natural antibodies that recognize a human brain lectin

We have recently identified oligoclonal IgG antibodies that are related to a human brain lectin (HBL14) from serum and cerebrospinal fluid of patients with neurological disorders. They were termed lectin-like IgG (L-IgG) (Joubert-Caron et al., 1994a,b). In this paper, the occurrence of antibodies reactive both towards HBL14 and L-IgG was investigated. Binding of antibodies to HBL14 was demonstrated by solid-phase ELISA and chromatography on immobilized HBL14. Fab fragments of these antibodies were also shown to bind to HBL14. The specificity of the antibodies towards HBL14 was studied using a panel of different antigens. Our data show that individual sera from healthy people as well as a pool of immunoglobulins from 80 blood donors contain an IgG autoreactivity to HBL14, while no IgM autoreactivity was detected. Anti-HBL14 antibodies from sera were purified using affinity chromatography on immobilized HBL14. Affinity chromatography further allowed us to demonstrate that the binding of anti-HB14 antibodies was mediated through their Fab fragments. A higher amount of anti-HBL14 antibodies was purified using a L-IgG-depleted fraction of sera. The binding of anti-HBL14 antibodies to L-IgG was confirmed by ELISA. Finally, anti-HBL14 antibodies were found to be polyreactive. These results indicate the occurrence of a novel class of natural antibodies reactive towards a human brain lectin and suggest that these antibodies may participate in immunoregulatory mechanisms probably though idiotypic/anti-idiotypic interaction.

Use of thiophilic adsorption in the purification of biotinylated Fab fragments

A method for the purification and biotinylation of Fab fragments, using thiophilic adsorption (T-gel), is described. The T-gel was used to purify an IgG fraction directly in the buffer suitable for biotinylation, and to adsorb intact IgGs and papain after enzymatic digestion. For the final step, Fc fragments were removed with a protein A column.

Phosphorylation and palmitoylation of the human D2L dopamine receptor in Sf9 cells

We have expressed and biochemically characterized the human D2long (D2L) dopamine receptor isoform using the baculovirus/Sf9 cell system. The expressed receptor bound ligands with a pharmacological profile similar to that reported for neuronal and cloned D2L receptors expressed in mammalian cell lines. Dopamine binding to D2L receptor was sensitive to guanine nucleotides, indicating receptor coupling to endogenous G proteins. A D2L receptor-specific antibody identified two major protein species at approximately 44 kDa and at approximately 93 kDa in immunoblots, suggesting the presence of D2L receptor monomers and dimers. Both species were purified by immunoprecipitation from digitonin-solubilized preparation of cells expressing D2L receptor prelabeled with 32P(i) or [3H]-palmitate. These results constitute the first direct evidence for D2L receptor phosphorylation and palmitoylation.

The extracellular domain of the epidermal growth factor receptor. Studies on the affinity and stoichiometry of binding, receptor dimerization and a binding-domain mutant

The binding of epidermal growth factor (EGF) or an EGF-like growth factor to the EGF receptor is the initial event which leads to receptor activation, and consequently the induction of cell growth. In order to study this binding interaction in detail, we produced the extracellular domain of the EGF receptor (EGFR) using the baculovirus expression system. Affinity-labeling and Western-blot analyses revealed that the baculovirus-infected insect cells secrete active EGFR extracellular domain relatively efficiently, however a significant amount of inactive EGFR extracellular domain is retained within the cells. The apparent dissociation constant (Kd) of the secreted EGFR extracellular domain for EGF and transforming growth factor alpha (TGF-alpha), as determined using an immobilized receptor binding assay, was approximately 200 nM. Interestingly, this Kd value is 30-40-fold lower than that of the full-length EGFR derived from detergent-solubilized A431 cell membranes. The stoichiometry of binding of the EGFR extracellular domain to EGF and TGF-alpha was examined by band-shift analysis on non-denaturing PAGE and was estimated to be 1:1. We have also shown, using sedimentation equilibrium analysis, that ligand binding induces significant dimerization of the EGFR extracellular domain. Finally, we carried out site-specific mutagenesis on the EGFR extracellular domain in order to define the ligand-binding region. We identified amino acid residues which are close to the binding site since they are common to the epitopes of several ligand-competitive monoclonal antibodies. However, these residues do not contribute directly to ligand binding since the affinity of the mutated EGFR extracellular domain for EGF and TGF-alpha was unaffected.

Changes in S-type lectin localization in neuroblastoma cells (N1E115) upon differentiation

The distribution of a 14.4 kDa S-type lectin was examined in murine neuroblastoma cells, either undifferentiated or after differentiation induced by dibutyryl-cyclic adenosine monophosphate. In undifferentiated cells the immunoreactivity was detected extracellularly, associated with the plasma membrane and in bulges released into the extracellular milieu. Important modifications of the lectin localization were associated with the differentiation process that induced an increased cytosolic expression and a decreased externalization. Possible functions for the lectin expressed intracellularly in the differentiated cells are also considered.

Evidence for a role of protein kinase C in the activation of the pyruvate dehydrogenase complex by insulin in Zajdela hepatoma cells

The signal transduction pathway involved in the activation of pyruvate dehydrogenase (PDH) by insulin is still unknown. In this study, we have examined the possible involvement of protein kinase C (PKC) in the process. In addressing this question, we examined (1) the insulin-like effects of the PKC activator 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) on the PDH complex, (2) the effects of various PKC inhibitors on the PDH activation by insulin, and (3) the response of PKC-depleted cells to insulin. We used as an experimental model Zajdela hepatoma cultured (ZHC) cells, which have been demonstrated to be responsive to physiological doses of insulin. Half-maximal and maximal stimulations of the PDH complex by insulin were observed at 0.05 and 5 nmol/L, respectively. Stimulation of PDH activity by insulin (5 nmol/L) occurred within 5 minutes of incubation and was maximal (+70%) at 7.5 minutes. In the presence of PMA (162 nmol/L), enzyme activity increased within 30 seconds, was maximal (+90%) at 5 minutes, and was no longer detectable after 10 minutes. Total PDH activity was unchanged by insulin or PMA treatment. The effects of PMA and insulin on basal PDH activity were not additive. Moreover, various inhibitors of PKC--staurosporine, sphingosine, acridine orange--completely blocked the stimulation of PDH activity induced by insulin or PMA. A 17-hour treatment of ZHC cells with 500 nmol/L PMA efficiently downregulated PKC, as attested by the marked decrease in the enzyme activity and the loss of phorbol 12,13-dibutyrate binding to intact cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin receptor mutation at tyrosines 1162 and 1163 alters both receptor serine phosphorylation and desensitization

Chinese hamster ovary (CHO) cells expressing human insulin receptor (hIR) of the wild-type (CHO R) or hIR mutated at tyrosines 1162 and 1163 (CHO Y2) were compared for agonist-induced receptor phosphorylation of serine/threonine residues and receptor desensitization. Relative to CHO R cells, CHO Y2 cells exhibited a marked decrease in their response to insulin and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) for hIR phosphorylation on serine residues. Moreover, the tyr1162,1163 mutant hIR could not be normally phosphorylated by purified protein kinase C (PKC) in vitro. Finally, in contrast to CHO R cells, CHO Y2 cells were refractory to PMA-induced IR desensitization for subsequent activation by insulin of exogenous tyrosine kinase and glycogen synthesis. These results strongly suggest that the replacement of tyrosines 1162 and 1163 by phenylalanine residues changes the IR beta-subunit conformation and thus impedes phosphorylation of the IR at crucial serine residues and prevents PMA-induced desensitization. This supports the hypothesis that IR serine phosphorylation and desensitization are related.

Oligoclonal beta-galactoside-binding immunoglobulins antigenically related to 14 kDa lectin in human serum and cerebrospinal fluid: purification and characterization

1. An antiserum raised against a 14 kDa beta-galactoside specific lectin from human brain (HBL14) was used to probe blots from samples of serum and cerebrospinal fluid. The only HBL14-immunoreactive material detected was heavy and light chains of a beta-galactoside-binding IgG fraction (lectin-like IgG). 2. Lectin-like IgG, as well as IgG Fab fragments, compete with HBL14 for binding either to anti-HBL14 antibody or to a lactosyl polyacrylamide-based copolymer. 3. Purification of lectin-like IgG was obtained by affinity chromatography on immobilized rabbit anti-lectin immunoglobulins. The carbohydrate-binding specificity of the purified molecules was restricted to beta-Gal-containing structures and close to the HBL14 one.

Normal qualitative and quantitative Tc-99m sestamibi myocardial SPECT: spectrum of intramyocardial distribution during exercise and at rest

Exercise myocardial perfusion imaging with Tc-99m sestaMIBI is routinely used to detect underlying coronary stenoses. Ischemia is diagnosed in regions that display decreased tracer uptake during exercise as compared to rest. Tc-99m sestaMIBI SPECT images of 42 healthy volunteers were assessed both qualitatively (tomographic slices) and quantitatively (sectored polar map) for potential sources of misinterpretation. On the myocardial tomographic slices, the most common culprit artifacts were diaphragmatic attenuation and bowel interposition, which caused fixed or reversible "perfusion defects" in the inferior and posterior regions (in 19/35 abnormal segments), and artifacts related to the presence and shift of hot spots (observed in 11/28 men; in women, they were more difficult to demonstrate because of the overriding effect of breast attenuation). Hot spots shifts between exercise and rest usually resulted in pseudo-reversible defects in the anterolateral and lateral walls. The quantified polar map display of the myocardium showed a physiologic decrease in sestaMIBI activity in the basal anterolateral and basal posterolateral areas in men during exercise. There are many normal variants that may mimic coronary artery disease on tomographic sestaMIBI images. Before reporting an area of decreased activity as either a fixed or reversible perfusion defect, the interpreter should ensure that it does not represent an artifact or a normal variation in the intramyocardial distribution of sestaMIBI during exercise.

Desensitization, phosphorylation and palmitoylation of the human dopamine D1 receptor

The regulation and post-translational modifications of the human dopamine D1 receptor were studied in the baculovirus-eukaryotic cell expression system. Baculovirus constructs containing either the DNA encoding the dopamine D1 receptor or a DNA encoding a c-myc epitope tagged dopamine D1 receptor (c-myc-dopamine D1 receptor) were used to infect Spodoptera frugiperda (Sf9) insect cells. Expressed dopamine D1 and c-myc-dopamine D1 receptors bound agonists and antagonists with affinities and a rank order of potency characteristic of a classical dopamine D1 receptor pharmacological profile. In membrane preparations from cells expressing c-myc-dopamine D1 receptor, the photoaffinity label [125I](3-methyl-2-[4'-azidophenyl]-2,3,5-tetrahydro-2H-3-benzazepine) ([125I]MAB) bound specifically upon photolysis. A major broad band of approximately 48 kDa was detected. This species was identified in immunoblots by the monoclonal antibody raised against the c-myc epitope of c-myc-dopamine D1 receptor was isolated by immunoprecipitation from whole cells and was shown to be post-translationally modified by phosphorylation and palmitoylation. Exposure of cells expressing c-myc-dopamine D1 receptor to dopamine for 15 min resulted in a reduction in the maximal dopamine stimulated adenylyl cyclase activity, which was accompanied by an increased phosphorylation of the receptor and a rapid redistribution of surface c-myc-dopamine D1 receptor as detected by in situ immunofluorescence. Dopamine exposure also resulted in an increased level of incorporation of [3H]palmitic acid into the receptor. Thus, we provide the first evidence that the human dopamine D1 receptor undergoes agonist-dependent desensitization, phosphorylation and palmitoylation.

Insulin receptor autophosphorylation sites tyrosines 1162 and 1163 control both insulin-dependent and insulin-independent receptor internalization pathways

We previously reported that Chinese hamster ovary (CHO) cell lines overexpressing mutated human insulin receptors (hIRs) in which the tyrosine residues 1162 and 1163 were replaced by phenylalanines (CHO-Y2) exhibited a marked defect in hormone-induced receptor internalization as compared to CHO transfectants overexpressing wild-type hIRs (CHO-R). These two cell lines are now used to compare the role of tyrosines 1162-1163 in basal and ligand-stimulated receptor internalization as well as in receptor turnover. We show here that (1) in CHO-Y2 cells, basal endocytosis, like insulin-induced internalization, was markedly altered despite normal receptor turnover and (2) in both CHO-R and CHO-Y2 cells, basal receptor endocytosis was altered by tunicamycin, an inhibitor of protein N-glycosylation, whereas insulin-induced internalization was not. These results support a role for tyrosines 1162-1163 of the IR beta-subunit major autophosphorylation domain in both basal and ligand-stimulated receptor endocytosis and provide evidence that the two processes follow distinct pathways.

Regional cerebral blood flow trends in head injured patients with focal contusions and cerebral edema

Focal contusions following head injury may be associated with focal or diffuse cerebral edema. Early global hyperemia and perifocal hyperemia may play a role in cerebral edema, although causal relationships have yet to be clearly been defined. We studied 27 patients with head injury (admission GCS 3-12) resulting in focal contusions (without evidence of subarachnoid, intraventricular or intraparenchymal hemorrhage by CT). Patients were studied with ICP monitors, head CTs, and intravenous 133Xenon regional cerebral perfusion studies serially over several days post injury. Low cortical blood flow and a low mean CBF15 flow were evident on the day of the injury. Additionally, F1 analysis indicated significantly (p < 0.05) greater cortical blood flow in the surrounding brain (mean 60 cc/100 g/min) compared to the contusion area (mean 43 cc/100 g/min) on the day of trauma. Mean regional CBF remained below normal in the contused areas (CBF15 < 35 cc/100 g/min), however the cortical flow increased in the first few days post-injury (peak F1 = 95 cc/100 g/min on day 3) then decreased to sub-normal levels. The mean CBF in the surrounding brain was low on the day of injury (CBF15 = 29 cc/100 g/min), although higher than the contused area, and increased to a peak of 45 cc/1009/min on day 3 posttrauma. Cortical flow in the surrounding brain, however, exhibited a different trend. The mean F1 was low on the day of trauma and significantly higher one day after trauma (mean 105 cc/100 g/min). Only 15 of the 27 patients with focal contusions had evidence of cerebral edema. Eleven of these exhibited focal edema and 4 exhibited diffuse edema. Focal edema developed over the first few days posttrauma as seen in followup CT, whereas patients with diffuse edema exhibited edema on the admission CT. Initial oligemia in the contused areas was associated with a subsequent hyperemic rim about the contusion. Focal hyperemia was associated with focal edema in 41% of the patients, whereas diffuse edema appeared to be independent of the hyperemic response in contusions.

Human serotonin1B receptor expression in Sf9 cells: phosphorylation, palmitoylation, and adenylyl cyclase inhibition

Analysis of the primary protein structure of the human serotonin1B (5-HT1B) receptor reveals consensus sites for phosphorylation and a putative site for palmitoylation. To investigate these posttranslational modifications, we have expressed a c-myc epitope-tagged 5-HT1B (m5-HT1B) receptor in Sf9 cells. This strategy enabled receptors to be detected by immunoblot analysis and purified by immunoprecipitation using a monoclonal antibody, 9E10, specific for the c-myc epitope. Agonist radioligand [3H]5-HT binding studies showed that the expressed 5-HT1B and m5-HT1B receptors displayed the characteristic pharmacological profile of the neuronal 5-HT1B receptor. The expressed receptors displayed both high- and low-affinity states for [3H]5-HT, suggesting that the receptors were coupled to endogenous G-proteins. Indeed, agonist binding to the high-affinity receptor state was regulated in the presence of GTP gamma S, Gpp(NH)p, and pertussis toxin. [32P]ADP-ribosylation experiments identified a major approximately 41-kDa ADP-ribosylated protein present in Sf9 membranes that comigrated with partially purified bovine brain Gi alpha/G(o) alpha subunits. Measurements of adenylyl cyclase activity in membranes from cells expressing m5-HT1B receptors showed that serotonergic agonists mediated the inhibition of adenylyl cyclase activity with a rank order of potency comparable to their affinity constants. Immunoblot analysis of membranes prepared from cells expressing m5-HT1B receptors and photoaffinity labeling of the immunoprecipitated material revealed photolabeled species at approximately 95 and at approximately 42 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of lectin-ganglioside interactions by high-performance liquid affinity chromatography

A high-performance affinity column containing immobilized modified GM1 (lyso-GM1) was used to study the binding of an endogenous human brain lectin (HBL) in comparison with other carbohydrate-binding proteins. The proteins are previously converted into biotinylated derivatives. Detection of biotinylated proteins in the eluates by a microtitre plate assay ensures good sensitivity. The maximum binding capacity of the adsorbent for HBL is obtained in Tris buffer supplemented with beta-mercaptoethanol. The binding is inhibitable by specific sugar. It is concluded that the use of immobilized glycolipids in analytical high-performance liquid affinity chromatographic methods may serve as models in the study of interactions between gangliosides and carbohydrate-binding proteins.

Agonist-modulated palmitoylation of beta 2-adrenergic receptor in Sf9 cells

The palmitoylation of the human beta 2-adrenergic receptor (beta 2-AR) was studied in recombinant baculovirus-infected insect Sf9 cells. At 48 h post-infection, a high level expression of an epitope-tagged beta 2-AR (10-25 pmol/mg protein) was detected by [125I]iodocyanopindolol ([125I]CYP) binding assays. The identity of the receptor was confirmed both by photoaffinity labeling and immunoblotting. The fusion receptor displayed typical beta 2-AR pharmacological properties and conferred a beta-adrenergic sensitive adenylyl cyclase activity to the Sf9 cells. Moreover, exposure of the Sf9 cells to the beta-adrenergic agonist isoproterenol induced a rapid desensitization of the receptor-stimulated adenylyl cyclase activity. Purification of the epitope-tagged beta 2-AR by immunoprecipitation as well as by alprenolol-Sepharose affinity chromatography revealed that the receptor is covalently modified with palmitic acid in the insect cells as is observed in mammalian cells. In addition, short-term incubation of the cells with isoproterenol led to a specific increase in the incorporation of [3H]palmitate in the receptor, consistent with a rapid agonist-modulated turnover of the beta 2-AR-attached palmitic acid. These results suggest that agonist-mediated regulation of beta 2-AR post-translational palmitoylation could represent an other regulatory process for G protein-coupled receptors.

Use of an immobilized human endogenous lectin for the purification of complementary ligands

1. A galactoside-specific endogenous lectin isolated from human brain was covalently immobilized on divinylsulfone-activated agarose. This highly selective affinity adsorbent proved to be useful in purifying soluble protein ligands. 2. The maximum binding capacity of the adsorbent for complementary proteins was calculated to be 618 micrograms per g of gel (wet resin). 3. Sequential elutions using 0.1 M lactose, 0.3 M lactose and 0.5 M NaCl, and competition assays using incorporation in the presence 0.1 M lactose revealed differences in lectin-ligand interactions.

Differential role of insulin receptor autophosphorylation sites 1162 and 1163 in the long-term insulin stimulation of glucose transport, glycogenesis, and protein synthesis

The long-term regulatory effect of insulin on glucose transport activity and glucose transporter expression was examined in Chinese hamster ovary (CHO) transfectants that overexpress either human insulin receptors of the wild type (CHO-R cells) or human insulin receptors mutated at two major autophosphorylation sites, Tyr1162 and Tyr1163 (CHO-Y2 cells). Previous studies showed that, when acutely stimulated by insulin, CHO-Y2 cells exhibit decreased receptor kinase activity along with decreased signaling of several pathways, including that for glucose transport, as compared with CHO-R cells. We now report the following. (i) When treated for 24 h with insulin (10(-10) to 10(-6) M), CHO-R and CHO-Y2 cells displayed closely similar concentration-dependent increases in 2-deoxyglucose uptake. In both transfectants, the maximal insulin-induced increase (approximately 3.5-fold) in uptake was cycloheximide-sensitive and was paralleled by equivalent increases in the levels of GLUT-1 immunoreactive protein and mRNA. (ii) By contrast, under similar conditions, CHO-Y2 cells exhibited a marked decrease in their response to insulin for [U-14C]glucose incorporation into glycogen (decreased sensitivity and maximal responsiveness) and for [U-14C]leucine incorporation into protein (decreased sensitivity) as compared with CHO-R cells. (iii) After a 24-h treatment with 10(-7) M insulin, CHO-R (but not CHO-Y2) cells showed a decreased ability to respond to a subsequent acute insulin stimulation of either receptor exogenous kinase activity or 2-deoxyglucose uptake as compared with respective untreated controls. These results indicate that (i) insulin receptors mutated at Tyr1162 and Tyr1163 retain normal signaling of the long-term stimulatory effect of insulin on glucose transport activity and GLUT-1 expression, but not on glycogenesis and overall protein synthesis; (ii) these three insulin signaling pathways may be triggered by distinct domains of the insulin receptor beta-subunit; and (iii) wild-type (but not twin-tyrosine mutant) receptors undergo negative regulation by chronic insulin treatment for subsequent signaling of acute biological actions of insulin.

Electrophoretic study of conformational changes of a human soluble beta-D-galactoside-binding lectin upon storage

Human brain lectin (HBL), a beta-galactoside specific soluble lectin, was purified by affinity chromatography. An alkylated derivative of this lectin was also prepared. Both native and modified molecules were conserved at -20 degrees C in the presence or absence of beta-mercaptoethanol, a reducing agent which was described to maintain the lectin activity in vitro or in the presence of beta-mercaptoethanol and lactose. The impact of storage conditions, over one year, on the native and derivated lectins, was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing and titration curve, using the PhastSystem (Pharmacia). Western-blot analysis using an anti-HBL antibody and size-exclusion high performance liquid chromatography were used to complete the study. The subunit M(r)s were estimated before freezing (T0) and after three and twelve months (T3, T12). They were comparable for all preparations. In all samples tested, isoelectric focusing demonstrated the existence of at least three acidic proteins, with the pI ranging between 4.7-4.9. Titration curves clearly showed pH-dependent conformational changes, resulting in a panel of differently charged molecular species, some of which may be related to different oxidative states of the cysteine residues. We concluded that lectin can be stored at -20 degrees C for at least one year before use as a reagent since the modifications revealed by electrophoretic analysis do not alter the hemagglutination activity and carbohydrate binding properties. The immunoreactivity also remained unchanged.

Development of screening methods for detection of carbohydrate-binding proteins by use of soluble glycosylated polyacrylamide-based copolymers

Mammalian endogenous carbohydrate-binding proteins (lectins) play fundamental roles in a variety of mechanisms of interactions both at the molecular and cellular levels. We have investigated the binding of one of them (human brain lectin) to soluble acrylamide copolymerized with derivatives of either lactose (O-beta-lactosyloxyallylallylaminoacrylamide copolymer) or D-mannose (D-alpha-mannosyloxyallylallylaminoacrylamide copolymer) in direct enzyme affinoassays, in an attempt to develop simple procedures for detection and estimation of its carbohydrate-binding activity. Biotinylated plant lectins were utilized as reference standards. Affinoassays employed the polymer dotted on nitrocellulose and the polymer coated on microtiter plates as well as detection of bound biotinylated lectin by streptavidin/horseradish peroxidase reagent. Both assays provided reproducible binding, inhibitable by specific sugars. The microtiter plate assay is well suited to sensitive detection of the negative endogenous lectin by competition with biotinylated brain lectin. We conclude that the use of derivatized acrylamide in dotting and microtiter plate assays may prove practical for detection of endogenous lectins and that such polymers may serve as model substances in the study of biological partners of these carbohydrate-binding proteins.

Baculovirus expression of mammalian G protein alpha subunits

Complementary DNAs encoding three subtypes of the alpha subunit (alpha i-1, alpha o and alpha s) of rat guanyl nucleotide regulatory proteins were used to construct recombinant baculoviruses which direct high-level expression of the corresponding proteins in cultured Sf9 insect cells. The expressed proteins were recognized by polyclonal antisera specific for the different alpha chains, and co-migrated with the native proteins from rat brain membranes in immunoblotting analyses. Soluble and particulate forms of all three immunoreactive alpha chains were observed following ultracentrifugation of cell lysates. Biosynthetic radiolabelling of infected cells with [35S]methionine or [3H]myristate showed that both soluble and particulate forms of alpha i-1 and alpha o were myristoylated; in contrast, alpha s did not incorporate myristate. The soluble fractions from cells expressing alpha chains showed high levels of GTP-binding activity over that observed in uninfected cells, or in cells infected with wild-type virus. The peak expression levels observed at 72 h post-infection were highest for alpha o at ca. 400 pmol of GTP-gamma-35S/mg protein, or roughly 2% of the total soluble protein. The results of this work show that the baculovirus system can be employed for high-level production of mammalian G protein alpha chains which retain GTP-binding activity and are appropriately modified by myristoylation.