Molecular characterization and diagnostic value of Taenia solium low-molecular-weight antigen genes

Neurocysticercosis (NCC) caused by infection with the larvae of Taenia solium is an important cause of neurological disease worldwide. In order to establish an enzyme-linked immunosorbent assay (ELISA) for this infection using recombinant proteins, we carried out molecular cloning and identified four candidates as diagnostic antigens (designated Ag1, Ag1V1, Ag2, and Ag2V1). Except for Ag2V1, these clones could encode a 7-kDa polypeptide, and Ag2V1 could encode a 10-kDa polypeptide. All of the clones were very similar. Except for Ag2V1, recombinant proteins were successfully expressed using an Escherichia coli expression system. Immunoblot analysis of NCC patient sera detected recombinant proteins, but because reactivity to recombinant Ag1 was too weak, Ag1 was not suitable as an immunodiagnostic antigen. So, Ag1V1 and Ag2 were chosen as ELISA antigens, and the Ag1V1/Ag2 chimeric protein was expressed. Of 49 serum samples from NCC patients confirmed to be seropositive by immunoblot analysis, 44 (89.7%) were positive by ELISA. No assays of serum samples from patients with other parasitic infections recognized the Ag1V1/Ag2 chimeric protein. The Ag1V1/Ag2 chimeric protein obtained in this study had a high value for differential immunodiagnosis.

Mitochondrial genetic code in cestodes

The flatworm mitochondrial genetic code, which has been used for all species of the Platyhelminthes, is mainly characterized by AUA codon for isoleucine, AAA codon for asparagine and UAA codon for tyrosine. In eight species of cestodes (Echinococcus multilocularis, Echinococcus granlosus, Taenia solium Taenia saginata, Taenia hydatigena, Taenia crassiceps, Hymenolepis nama and Mesocestoides corti), the cytochrome c oxidase subunit I (COI) genes were partially sequenced to verify this genetic code. Comparison of the COI-encoding nucleotide sequences with those of human, sea urchin, fruit fly, nematode and yeast indicated that the assignments of AUA and AAA codons are adequate for cestodes. In addition, the nucleotide sequences of ATPase subunit 6 (ATP6) gene and its flanking region were compared to examine initiation and stop codons. In the related species of T. solium and T. saginata, the deduced amino acid sequences of ATP6 were homogeneous; however, the conversion of initiation codon AUG into GUG was observed in T. saginata. We also found the similar conversion in T. crassiceps. The C-terminal sequences of putative ATP6 proteins were highly conserved among the eight species and the stop codon UAG was altered to UAA in all Taenia species. The features of the gene-junctional region between NADH dehydrogenase subunit 4 (ND4) and glutamine tRNA (tRNAGln) genes also supported that UAA serves as a stop codon. Based on these results, we propose that the flatworm mitochondrial code should be modified for cestodes, particularly, in an initiating methionine codon (GUG) and a terminating codon (UAA).

Chronic sulfonylurea treatment and hyperglycemia aggravate disproportionately elevated plasma proinsulin levels in patients with type 2 diabetes

It is established that disproportionately elevated plasma proinsulin levels occur in patients with Type 2 diabetes. In the present study, multivariate analysis was performed to determine what factors contributed to the disproportionately elevated plasma proinsulin levels in Japanese patients with Type 2 diabetes (n=276). Results from univariate analysis showed that both fasting proinsulin/C-peptide ratio and proinsulin/IRI ratio were approximately 2-fold higher in patients with Type 2 diabetes than those in healthy nondiabetic subjects (n=45). In patients with Type 2 diabetes, both proinsulin/C-peptide ratio and proinsulin/IRI ratio were significantly positively correlated with fasting plasma glucose level (FPG) and HbA1c. Neither proinsulin/C-peptide ratio nor proinsulin/IRI ratio was significantly correlated with BMI. Sulfonylurea-treated subjects had a significant elevation in both proinsulin/C-peptide ratio and proinsulin/IRI ratio compared with diet-treated subjects, whereas nonsulfonylurea hypoglycemic agent-treated subjects did not. Multivariate analysis confirmed that sulfonylurea treatment and FPG were significant determinants of both fasting proinsulin/C-peptide ratio (P=0.006 and P=0.030, respectively) and proinsulin/IRI ratio (P=0.003 and P=0.016, respectively) in patients with Type 2 diabetes. These results imply that disproportionate hyperproinsulinemia may reflect an excessive overwork of beta cells under chronic sulfonylurea treatment as well as hyperglycemia.

Reconstitution of brefeldin A-induced golgi tubulation and fusion with the endoplasmic reticulum in semi-intact chinese hamster ovary cells

The fungal metabolite brefeldin A (BFA) induces the disassembly of the Golgi complex in mammalian cells. The drug seems to accentuate tubule formation and causes the subsequent fusion with the endoplasmic reticulum (ER). To investigate the biochemical requirements and kinetics of BFA-induced Golgi disassembly, we have reconstituted the process of green fluorescent protein-tagged Golgi complex disassembly in streptolysin O-permeabilized semi-intact Chinese hamster ovary cells. For quantitative analysis of the morphological changes to the Golgi complex in semi-intact cells, we developed a novel morphometric analysis. Based on this analysis, we have dissected the BFA-induced Golgi disassembly process biochemically into two processes, Golgi tubule formation and fusion with the ER, and found that the formation is induced by only ATP and the residual factors in the cells and that the subsequent fusion is mediated in an N-ethylmaleimide-sensitive factor-dependent manner via Golgi tubules. Tubulation occurs by two pathways that depend on either microtubule integrity or exogenously added cytosol. In the presence of GTPgammaS, coat protein I inhibited the Golgi tubule fusion with the ER but showed no apparent effect on tubulation. Additionally, we analyzed the kinetics of tubulation and fusion independently in nocodazole-treated and -untreated semi-intact cells and found that tubulation is a rate-limiting step of the Golgi disassembly.

Single-molecule imaging of EGFR signalling on the surface of living cells

The early events in signal transduction from the epidermal growth factor (EGF) receptor (EGFR) are dimerization and autophosphorylation of the receptor, induced by binding of EGF. Here we observe these events in living cells by visualizing single molecules of fluorescent-dye-labelled EGF in the plasma membrane of A431 carcinoma cells. Single-molecule tracking reveals that the predominant mechanism of dimerization involves the formation of a cell-surface complex of one EGF molecule and an EGFR dimer, followed by the direct arrest of a second EGF molecule, indicating that the EGFR dimers were probably preformed before the binding of the second EGF molecule. Single-molecule fluorescence-resonance energy transfer shows that EGF-EGFR complexes indeed form dimers at the molecular level. Use of a monoclonal antibody specific to the phosphorylated (activated) EGFR reveals that the EGFR becomes phosphorylated after dimerization.

Novel prenyltransferase gene encoding farnesylgeranyl diphosphate synthase from a hyperthermophilic archaeon, Aeropyrum pernix. Molecularevolution with alteration in product specificity

Prenyltransferases catalyse sequential condensations of isopentenyl diphosphate with allylic diphosphates. Previously, we reported the presence of farnesylgeranyl diphosphate (FGPP) synthase activity synthesizing C25 isoprenyl diphosphate in Natronobacterium pharaonis which is a haloalkaliphilic archaeon having C20-C25 diether lipids in addition to C20-C20 diether lipids commonly occurring in archaea [Tachibana, A. (1994) FEBS Lett. 341, 291-294]. Recently, it was found that a newly isolated aerobic hyperthermophilic archaeon, Aeropyrum pernix, had only C25-C25 diether lipids, not the usual C20-containing lipids [Morii, H., Yagi, H., Akutsu, H., Nomura, N., Sako, Y. & Koga, Y. (1999) Biochim. Biophys. Acta 1436, 426-436]. In this report, we describe the isoloation from A. pernix of the novel prenyltransferase gene, fgs, encoding FGPP synthase. The protein encoded by fgs was expressed in Escherichia coli as a glutathione S-transferase fusion protein and produced FGPP as a final product. Phylogenetic analysis of fgs with other prenyltransferases revealed that the short-chain prenyltransferase family is divided into three subfamilies: bacterial subfamily I, eukaryotic subfamily II, and archaeal subfamily III. fgs is clearly contained within the archaeal geranylgeranyl diphosphate (GGPP) synthase group (subfamily III), suggesting that FGPP synthase evolved from an archaeal GGPP synthase with an alteration in product specificity.

Resurgence of cases of epileptic seizures and burns associated with cysticercosis in Assologaima, Jayawijaya, Irian Jaya, Indonesia, 1991-95

Historically, neurocysticercosis (NCC) caused by the larval stage, cysticercus or cysticerci, of the pork tapeworm Taenia solium was recognized in Paniai District, western Irian Jaya Province, Indonesia, in the early 1970s. In the 1990s, we observed a rapid increase in the number of cases of epileptic seizures and burns in Assologaima Sub-District, Jayawijaya District, eastern Irian Jaya. There were totals of 1120 new cases of burns and 293 new cases of epileptic seizures during 1991-95 in Assologaima where the number of inhabitants was 15,939. Histopathological examination of resected cysts from patients and a pig revealed that they were cysticerci of T. solium. DNA analysis of these cysts revealed that the nucleotide sequences of 391 base-pair fragments of the mitochondrial cytochrome c oxidase subunit 1 gene were exactly the same in those from patients and the pig. Although 3 of 391 base-pair fragments might differ from that of T. solium reported previously, there were no differences in the amino-acid sequences. Approximately 67% and 65% of persons with epileptic seizures and with subcutaneous nodules, respectively, showed antibody responses highly specific to cysticercosis. Therefore, most cases of epileptic seizures and burns were considered to be associated with cysticercosis in Irian Jaya.

Two family B DNA polymerases from Aeropyrum pernix, an aerobic hyperthermophilic crenarchaeote

DNA polymerase activities in fractionated cell extract of Aeropyrum pernix, a hyperthermophilic crenarchaeote, were investigated. Aphidicolin-sensitive (fraction I) and aphidicolin-resistant (fraction II) activities were detected. The activity in fraction I was more heat stable than that in fraction II. Two different genes (polA and polB) encoding family B DNA polymerases were cloned from the organism by PCR using degenerated primers based on the two conserved motifs (motif A and B). The deduced amino acid sequences from their entire coding regions contained all of the motifs identified in family B DNA polymerases for 3'-->5' exonuclease and polymerase activities. The product of polA gene (Pol I) was aphidicolin resistant and heat stable up to 80 degrees C. In contrast, the product of polB gene (Pol II) was aphidicolin sensitive and stable at 95 degrees C. These properties of Pol I and Pol II are similar to those of fractions II and I, respectively, and moreover, those of Pol I and Pol II of Pyrodictium occultum. The deduced amino acid sequence of A. pernix Pol I exhibited the highest identities to archaeal family B DNA polymerase homologs found only in the crenarchaeotes (group I), while Pol II exhibited identities to homologs found in both euryarchaeotes and crenarchaeotes (group II). These results provide further evidence that the subdomain Crenarchaeota has two family B DNA polymerases. Furthermore, at least two DNA polymerases work in the crenarchaeal cells, as found in euryarchaeotes, which contain one family B DNA polymerase and one heterodimeric DNA polymerase of a novel family.

A cambialistic SOD in a strictly aerobic hyperthermophilic archaeon, Aeropyrum pernix

The superoxide dismutase (SOD) gene of Aeropyrum pernix, a strictly aerobic hyperthermophilic archaeon, was cloned and expressed in Escherichia coli, and its gene product was characterized. The molecular mass of the protein, based on the deduced amino acid sequence, was 24.6 kDa. The sequence showed overall similarity to the sequences of known Mn- and Fe-SODs. The metal binding residues conserved in Mn- and Fe-SODs were also found in A. pernix SOD. When the SOD gene was expressed in E. coli cells, the product formed a homodimer, and contained both Mn and Fe. Metal reconstitution experiments showed that A. pernix SOD is cambialistic, i.e. active with either Fe or Mn. The specific activities were 906 U/mg with Mn and 175 U/mg with Fe. No loss of activity of Mn-reconstituted SOD was observed at 105 degrees C even after 5 h incubation. Sodium azide, an inhibitor of SODs, did not inhibit the Mn-reconstituted SOD from A. pernix even at concentrations up to 400 mM. This SOD from an aerobic hyperthermophilic archaeon, Aeropyrum pernix, was extremely thermostable and active with either Mn or Fe. With Mn as a metal cofactor, it was more thermostable, and less sensitive to sodium azide and sodium fluoride than with Fe.

Molecular cloning and characterisation of 23-kDa piroplasm surface proteins of Theileria sergenti and Theileria buffeli

The cDNA encoding a 23-kDa piroplasm membrane protein (p23) of Theileria sergenti Chitose (C)-type was isolated and its nucleotide sequence was determined. The gene encodes a polypeptide of 223 aa with a 28 residue N-terminal signal sequence and a hydrophobic, valine-rich, C-terminal transmembrane domain, as deduced from its nucleotide sequence. Southern blot hybridisation analysis proved that p23 gene was a single copy gene and had allelic forms of the gene in the parasite population. By PCR, the open reading frames of T. sergenti Ikeda (I)-type and Theileria buffeli (B)-type p23 were amplified from genomic DNA and their nucleotide sequences were also determined. Comparison of C-type sequence with that of I-type and B-type revealed 90.5% and 93.5% sequence similarity, respectively, at the aa level. These results suggest that a conserved molecule in these benign Theileria spp. could be a candidate antigen for the development of an anti-piroplasm vaccine.

Molecular characterization of a Haemaphysalis longicornis tick salivary gland-associated 29-kilodalton protein and its effect as a vaccine against tick infestation in rabbits

The use of tick vaccines in mammalian hosts has been shown to be the most promising alternative tick control method to current use of acaricides, which suffers from a number of limitations. However, the success of this method is dependent on the identification, cloning, and in vitro expression of tick molecules involved in the mediation of key physiological roles with respect to the biological success of a tick as a vector and pest. We have sequenced and characterized a Haemaphysalis longicornis tick salivary gland-associated cDNA coding for a 29-kDa extracellular matrix-like protein. This protein is expressed in both unfed and fed immature and mature H. longicornis ticks. The predicted amino acid sequence of p29 shows high homology to sequences of some known extracellular matrix like-proteins with the structural conservation similar to all known collagen proteins. Immunization with the recombinant p29 conferred a significant protective immunity in rabbits, resulting in reduced engorgement weight for adult ticks and up to 40 and 56% mortality in larvae and nymphs that fed on the immunized rabbits. We speculate that this protein is associated with formation of tick cement, a chemical compound that enables the tick to remain attached to the host, and suggest a role for p29 as a candidate tick vaccine molecule for the control of ticks. We have discussed our findings with respect to the search of tick molecules for vaccine candidates.

Expression of a major piroplasm surface protein of Theileria sergenti in sporozoite stage

A 32 kilodalton major piroplasm surface protein (MPSP) is expressed abundantly on the surface of intraerythrocytic piroplasms of Theileria sergenti and is considered to be a candidate antigen for vaccine development against piroplasmosis. In this study, transcripts of MPSP gene were detected in an expression cDNA library prepared from T. sergenti-infected tick salivary glands. Expression of MPSP in the sporozoite stage was also confirmed by immunoblot analysis. Its expression at the sporozoite and intraerythrocytic stages gives scope for possible induction of protective immunity being targeted at both stages by immunization with recombinant MPSP.

Cloning of a cysteine proteinase gene of Theileria sergenti

A cDNA encoding cysteine proteinase of Theileria sergenti was isolated from a piroplasm cDNA library and its nucleotide sequence was determined. The gene encodes a polypeptide of 402 amino acids with predicted molecular mass of 46.4 kDa. Analysis of the predicted amino acid sequence revealed a number of features common to known cysteine proteinases. Southern blot analysis showed that the cysteine proteinase gene was likely to be a single copy per genome.

A novel phosphoglycolipid archaetidyl(glucosyl)inositol with two sesterterpanyl chains from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1

The structures of two novel polar lipids (AGI and AI) of an aerobic hyperthermophilic archaeon, Aeropyrum pernix, were elucidated. AGI and AI were the only two major lipids and accounted for 91 mol% and 9 mol%, respectively, of total polar lipids of this organism. The core lipid of A. pernix total lipids consisted solely of 2,3-di-O-sesterterpanyl-sn-glycerol (C25,25-archaeol). The molecular weights of the free acid forms of AGI and AI were shown by FAB-mass spectrometry to be 1196 and 1034, respectively. AI was completely hydrolyzed by phosphatidylinositol-specific phospholipase C, while AGI was not hydrolyzed at all under the same condition for the hydrolysis of AI. The molar ratio of phosphate, myo-inositol, and glucose in AGI was 1.0:0.97:0.95. The positions of linkages between myo-inositol and glucose, and between myo-inositol and phosphate in AGI were determined by NMR analyses of intact AGI and glucosylinositol prepared from AGI. Finally, it was concluded that the structures of AGI and AI were 2,3-di-O-sesterterpanyl-sn-glycerol-1-phospho-1'-(2'-O-alpha-D-glu cosyl)- myo-inositol (C25,25-archaetidyl(glucosyl)inositol) and 2,3-di-O-sesterterpanyl-sn-glycerol-1-phospho-myo-inositol (C25,25-archaetidylinositol), respectively. This is the first example that a core lipid of whole polar lipids is composed of only one species C25,25-archaeol in one organism and that glucosylinositol is found in a polar lipid as a polar head group.

Purification and characterization of an intracellular heat-stable proteinase (pernilase) from the marine hyperthermophilic archaeon Aeropyrum pernix K1

A novel intracellular serine proteinase from the marine aerobic hyperthermophilic archaeon Aeropyrum pernix K1 (JCM 9820) that we designated pernilase was purified by ammonium sulfate precipitation, anionic-exchange chromatography, affinity chromatography, and gel filtration chromatography. The purified enzyme was composed of a single polypeptide chain with a molecular mass of 50 kDa as determined by SDS-PAGE. The proteinase had a broad pH profile (pH 5-10) with an optimum pH of 9.0 for peptide hydrolysis. The optimum temperature for enzyme activity was 90 degrees C. The enzyme was strongly inhibited by diisopropyl fluorophosphate (DFP) and phenylmethyl sulfonylfluoride (PMSF), suggesting that it corresponds to a serine proteinase. The enzyme was highly resistant to the reducing agents dithiothreitol and 2-mercaptoethanol but sensitive to the denaturing reagents guanidine-HCl and urea and also to the detergent sodium dodecyl sulfate (SDS). Pernilase showed high substrate specificity for Boc-Leu-Gly-Arg-MCA peptide. Thermostability of this enzyme showed half-lives of 85min at 100 degrees C and 12 min at 110 degrees C.

Regulation mechanism of the lateral diffusion of band 3 in erythrocyte membranes by the membrane skeleton

Mechanisms that regulate the movement of a membrane spanning protein band 3 in erythrocyte ghosts were investigated at the level of a single or small groups of molecules using single particle tracking with an enhanced time resolution (0.22 ms). Two-thirds of band 3 undergo macroscopic diffusion: a band 3 molecule is temporarily corralled in a mesh of 110 nm in diameter, and hops to an adjacent mesh an average of every 350 ms. The rest (one-third) of band 3 exhibited oscillatory motion similar to that of spectrin, suggesting that these band 3 molecules are bound to spectrin. When the membrane skeletal network was dragged and deformed/translated using optical tweezers, band 3 molecules that were undergoing hop diffusion were displaced toward the same direction as the skeleton. Mild trypsin treatment of ghosts, which cleaves off the cytoplasmic portion of band 3 without affecting spectrin, actin, and protein 4.1, increased the intercompartmental hop rate of band 3 by a factor of 6, whereas it did not change the corral size and the microscopic diffusion rate within a corral. These results indicate that the cytoplasmic portion of band 3 collides with the membrane skeleton, which causes temporal confinement of band 3 inside a mesh of the membrane skeleton.

Vaccine development against Theileria parasite

Bovine piroplasmosis caused by Theileria sergenti is a major cause of economical loss in grazing cattle in Japan. We found that parasite stocks and isolates consist of genetically and antigenically mixed population. To differentiate parasite populations bearing 2 allelic forms of p32, an immunodominant piroplasm surface protein, 2 sets of oligonucleotide primers were designed to amplify either of the 2 alleles by polymerase chain reaction (PCR). By using this allele-specific PCR, we found that the majority of T. sergenti-infected calves in Japan harbored mixed parasite populations with C and I type parasites. Amino acid sequence of p32 contains Lys-Glu-Lys (KEK) motif which is one of tripeptide necessary for malaria parasite to invade erythrocytes. We produced 2 vaccine candidates, recombinant baculovirus p32 and synthetic peptide containing KEK motif. Immunization of either recombinant p32 or synthetic peptide containing a KEK sequence with adjuvant resulted in low parasitemia and reduced the clinical symptoms compared to control calves. Interestingly, parasites with a p32 allelic form corresponding to one used as the immunogen were suppressed. Therefore, a cocktail vaccine containing KEK peptides derived from C and I type parasites is desired for control Theileria parasite infection in Japan.

Molecular characterization and postsplicing fate of three introns within the single rRNA operon of the hyperthermophilic archaeon Aeropyrum pernix K1

The single rRNA operon (arnS-arnL) of the hyperthermophilic archaeon Aeropyrum pernix K1 was sequenced. The DNA sequence data and detailed RNA analyses disclosed an unusual feature: the presence of three introns at hitherto undescribed insertion positions within the rRNA genes. The 699-nucleotide (nt) intron Ialpha was located at position 908 (Escherichia coli numbering [H. F. Noller, Annu. Rev. Biochem. 53:119-162, 1984]) of the 16S rRNA, while the 202-nt intron Ibeta and 575-nt intron Igamma were located at positions 1085 and 1927 (E. coli numbering), respectively, of the 23S rRNA. They were located within highly conserved sites which have been implicated as crucial for rRNA function in E. coli. All three introns were remarkably AT rich (41.5 to 43.1 mol% G+C) compared with the mature rRNAs (67.7 and 69.2 mol% G+C for 16S and 23S rRNAs, respectively). No obvious primary sequence similarities were detected among them. After splicing from rRNA transcripts in vivo, a large quantity of intronic RNAs were stably retained in the linear monomeric form, whereas a trace of topoisomeric RNA molecules also appeared, as characterized by their behavior in two-dimensional gel electrophoresis. Secondary structural models of the Ialpha-, Ibeta-, and Igamma-containing rRNA precursors agree with the bulge-helix-bulge motif. Two of the introns, Ialpha and Igamma, contained open reading frames whose protein translation exhibited no overall similarity with proteins reported so far. However, both share a LAGLI-DADG motif characteristic of homing endonucleases.

[Slowly progressive IDDM with rheumatoid arthritis and Hashimoto disease in high elderly]

We report a 79-year-old woman case of slowly progressive IDDM (SPIDDM) with rheumatoid arthritis (RA) and Hashimoto disease. High titer of anti-glutamic acid decarboxylase antibody (GAD) with a value of 16,400 U/ml (normal value: less than 5 U/ml) and deteriorated secretion of insulin, and clinical course led to the diagnosis of SPIDDM. Both anti-islet cell and anti-insulin antibodies were negative. One year prior to the diagnosis, at 78 years of age, she was newly diagnosed with NIDDM and had been medicated with sulfonylurea and voglibose, resulting her glucose levels well-controlled. Four months before admission, a gradual increase of plasma glucose was noticed, while oral hypoglycemic agents were fully administrated. On admission, her glycemic control was revealed as follows; a fasting blood glucose level of 458 mg/dl and an HbA1 C level of 14.3%. Urinary CPR was 22.5 micrograms day. Her insulin secretion was proved not to be induced with intravenous glucagon injection. Hyperinsulinemic euglycemic glucose clamp test showed the normal glucose uptake ratio; 9.5 mg/kg/min. Moderate doses of subcutaneous insulin (20 units daily) were effective on her diabetes control. She was newly diagnosed with Hashimoto disease that required thyroid hormone replacement 50 micrograms per day after having developed NIDDM. High titer of anti-thyroglobulin antibody (46.9 U/ml) and anti-thyroid peroxidase antibody (81.5 U/ml) were observed. The patient had been medicated for RA with anti-inflammatory drugs since her early seventieth. Rheumatoid factor was elevated to 127.7 IU/L and, anti-nuclear antibody (x 80) and anti-DNA antibody (x 80) were present. It may be of interest that a specific phenotype of HLA; A24 (9) and DR9 recognized to be susceptible to IDDM was detected in the high-elderly onset SPIDDM. Taken together HLA typing with her history of both RA and Hashimoto disease, our case may provide the information to the mechanism of pathogenesis of SPIDDM. Furthermore, to out knowledge, this is the first case of SPIDDM in the aged; 75-year-old or more.

Differentiation and quantification of Theileria sergenti piroplasm types using type-specific monoclonal antibodies

Antigenic properties of two representative allelic products of the major piroplasm surface protein (MPSP) of Theileria sergenti were studied. Sera from cattle infected with either of Ikeda and Chitose types of the parasite reacted strongly with homologous but weakly with heterologous recombinant antigens in immunoblotting. Monoclonal antibodies (MoAbs) produced against the both allelic products of MPSP parasites reacted only to the immunizing antigen. These results suggested that crossreactivity between two allelic products is very low inspite of relatively high homology in their amino acid sequences. Double staining of parasitized erythrocyte smear using type-specific MoAbs by an indirect immunofluorescent assay revealed that the set of MoAbs was useful for quantitative and differential detection of each type of parasite in mixed population.

Acquired thermotolerance and temperature-induced protein accumulation in the extremely thermophilic bacterium Rhodothermus obamensis

Temperature-induced changes in thermotolerance and protein composition were examined in heat-shocked cells and high-temperature-grown cells of the extremely thermophilic bacterium Rhodothermus obamensis. The survival at temperatures superoptimal for growth (90 and 95 degrees C) was enhanced in both heat-shocked cells and high-temperature-grown cells relative to that of cells grown at optimal temperatures. In a comparison of protein composition using two-dimensional gel electrophoresis, putative heat shock proteins (HSPs) and high-temperature growth-specific proteins (HGPs) were detected. N-terminal amino acid sequence analysis revealed that the putative HSPs were quite similar to the ATP-binding subunits of ABC transporters and the HGPs were proteins corresponding to domains II and III of elongation factor Tu. These results suggested that this extreme thermophile has developed temperature-induced responses that include increased survival under hyperthermal conditions, changes in protein composition, and also the production of novel HSPs.

Identification of B cell epitopes of a 30 kDa Babesia equi merozoite surface protein

A 30 kDa immunodominant surface antigen (p30) of Babesia equi has been used as a diagnostic antigen. The B cell epitopes on this molecule recognized by horse sera and monoclonal antibody (MAb) against p30, 36/133.97, were determined. A synthetic peptide of p30 with amino acid sequence of 123FYQEVLFKGFEAV135 exhibited strong positive reaction with the infected horse sera. In contrast, MAb 36/133.97 recognized different region of p30, as peptide synthesized with amino acid sequence of 27ASGAVVDFQLESI39 reacted strongly. In competitive inhibition ELISA, the binding of MAb 36/133.97 to recombinant p30 was inhibited by horse antibodies, although they did not recognize same or an overlapping epitope. The data on B cell epitopes in this study may be important in improving serodiagnostic methods of B. equi infection.

ppc, the gene for phosphoenolpyruvate carboxylase from an extremely thermophilic bacterium, Rhodothermus obamensis: cloning, sequencing and overexpression in Escherichia coli

The ppc gene, which encodes phosphoenolpyruvate carboxylase (PEPC) of an extremely thermophilic bacterium, Rhodothermus obamensis, was directly sequenced by the thermal asymmetric interlaced (TAIL) PCR method. An ORF for a 937 amino acid polypeptide was found in the gene. The ppc gene had a high G+C content (66.2 mol%) and the third position of the codon exhibited strong preference for G or C usage (85.0 mol%). The calculated molecular mass was 107,848 Da, which was consistent with the molecular mass of the enzyme as determined by SDS-PAGE (100 kDa). The amino acid sequence of R. obamensis PEPC was closely related to that of PEPC from another thermophile, a Thermus sp., and from a mesophile, Corynebacterium glutamicum, exhibiting 45.3% or 37.7% identity and 61.5% or 56.5% similarity, respectively. By Southern analysis, the ppc gene was found to be present in a single copy in the genomic DNA of this organism. The cloned gene was expressed in Escherichia coli using a pET expression vector system and a thermostable recombinant PEPC was obtained. Comparison of the deduced amino acid sequences of the thermophilic and mesophilic PEPCs revealed distinct or common preferences for specific amino acid composition and substitutions in the two thermophilic enzymes.

Structure of the erythrocyte membrane skeleton as observed by atomic force microscopy

The structure of the membrane skeleton on the cytoplasmic surface of the erythrocyte plasma membrane was observed in dried human erythrocyte ghosts by atomic force microscopy (AFM), taking advantage of its high sensitivity to small height variations in surfaces. The majority of the membrane skeleton can be imaged, even on the extracellular surface of the membrane. Various fixation and drying methods were examined for preparation of ghost membrane samples for AFM observation, and it was found that freeze-drying (freezing by rapid immersion in a cryogen) of unfixed specimens was a fast and simple way to obtain consistently good results for observation without removing the membrane or extending the membrane skeleton. Observation of the membrane skeleton at the external surface of the cell was possible mainly because the bilayer portion of the membrane sank into the cell during the drying process. The average mesh size of the spectrin network observed at the extracellular and cytoplasmic surfaces of the plasma membrane was 4800 and 3000 nm2, respectively, which indicates that spectrin forms a three-dimensionally folded meshwork, and that 80% of spectrin can be observed at the extracellular surface of the plasma membrane.

Cytoplasmic regulation of the movement of E-cadherin on the free cell surface as studied by optical tweezers and single particle tracking: corralling and tethering by the membrane skeleton

The translational movement of E-cadherin, a calcium-dependent cell-cell adhesion molecule in the plasma membrane in epithelial cells, and the mechanism of its regulation were studied using single particle tracking (SPT) and optical tweezers (OT). The wild type (Wild) and three types of artificial cytoplasmic mutants of E-cadherin were expressed in L-cells, and their movements were compared. Two mutants were E-cadherins that had deletions in the COOH terminus and lost the catenin-binding site(s) in the COOH terminus, with remaining 116 and 21 amino acids in the cytoplasmic domain (versus 152 amino acids for Wild); these are called Catenin-minus and Short-tailed in this paper, respectively. The third mutant, called Fusion, is a fusion protein between E-cadherin without the catenin-binding site and alpha-catenin without its NH2-terminal half. These cadherins were labeled with 40-nm phi colloidal gold or 210-nm phi latex particles via a monoclonal antibody to the extracellular domain of E-cadherin for SPT or OT experiments, respectively. E-cadherin on the dorsal cell surface (outside the cell-cell contact region) was investigated. Catenin-minus and Short-tailed could be dragged an average of 1.1 and 1.8 micron by OT (trapping force of 0.8 pN), and exhibited average microscopic diffusion coefficients (Dmicro) of 1.2 x 10(-10) and 2.1 x 10(-10) cm2/s, respectively. Approximately 40% of Wild, Catenin-minus, and Short-tailed exhibited confined-type diffusion. The confinement area was 0.13 micron2 for Wild and Catenin-minus, while that for Short-tailed was greater by a factor of four. In contrast, Fusion could be dragged an average of only 140 nm by OT. Average Dmicro for Fusion measured by SPT was small (0.2 x 10(-10) cm2/s). These results suggest that Fusion was bound to the cytoskeleton. Wild consists of two populations; about half behaves like Catenin- minus, and the other half behaves like Fusion. It is concluded that the movements of the wild-type E-cadherin in the plasma membrane are regulated via the cytoplasmic domain by (a) tethering to actin filaments through catenin(s) (like Fusion) and (b) a corralling effect of the network of the membrane skeleton (like Catenin-minus). The effective spring constants of the membrane skeleton that contribute to the tethering and corralling effects as measured by the dragging experiments were 30 and 5 pN/micron, respectively, indicating a difference in the skeletal structures that produce these two effects.

Cloning, sequence analysis, and expression in Escherichia coli of a gene coding for an enzyme from Bacillus circulans K-1 that degrades guar gum

A 2,048-bp nucleotide sequence containing a gene coding for an enzyme that degraded guar gum from Bacillus circulans K-1 was identified by polymerase chain reaction walking. This G-gene consisted of 1,551 nucleotides coding for a protein with Mr 55,242. The enzyme was overexpressed in Escherichia coli JM109 cells by the cloning the G-gene downstream of the lac Z promoter of pUC19. The molecular mass of recombinant G-enzyme estimated by SDS-PAGE was 62 KDa, close to that from strain K-1. Analysis of the recombinant enzyme showed GalNAc, Xyl, GlcNAc, Man, Glc, and Gal to account for 1.7%, 14.4%, 6.1%, 3.2%, 54.2%, and 10.4%, respectively, of the total monosaccharides. Polyacrylamide gel electrophoresis of this enzyme with staining gave a red band. The results suggested that the sugars accounted for the differences in the molecular masses. The recombinant enzyme had two kinds of N-terminal sequences, Thr-Met-Ile-Thr-Pro-Ser-Phe-Ala-Ser-Gly-Phe-Tyr-Val-Ile and Ile-Thr-Pro-Ser-Phe-Ala-Ser-Gly-Phe-Tyr-Val-Ile-Gly-Thr. Comparison of these sequences with the deduced N-terminal sequence coded for the G-gene showed that the amino acid, first Met, of the lac Z gene or the next residues Thr-Met in the recombinant enzyme were absent in the native enzyme. Methionines near and at the N-terminus of the mature protein probably were digested by methionine aminopeptidases of E. coli after translation. The properties of recombinant G-enzyme were similar to those of the enzyme from K-1 cells.

Control of Theileria sergenti infection by vaccination

Bovine piroplasmosis caused by Theileria sergenti is a major cause of economic loss in grazing cattle in Japan. Infected calves show chronic anaemia with intraerythrocytic piroplasms and occasionally die in severe cases. We found that parasite stocks and isolates consist of genetically and antigenically mixed populations. To differentiate parasite populations bearing 3 allelic forms of p32/34, an immunodominant piroplasm surface protein, 3 sets of oligonucleotide primers were designed to amplify either of 3 alleles by polymerase chain reaction (PCR). By using this allele-specific PCR, we found that the majority of T. sergenti-infected calves in Japan harbored mixed parasite populations bearing C and I type parasites. To control Theileria infection, we produced 2 vaccine candidates: recombinant baculovirus p32 and synthetic peptide containing Lys-Glu-Lys (KEK) motif. Immunization with either recombinant p32 or synthetic peptide containing KEK sequences with Freund's complete adjuvant resulted in low parasitemia and reduced the clinical symptoms compared to control calves. Interestingly, the parasite with the p32 allelic form corresponding to the one used as the immunogen was suppressed.

An extremely heat-stable extracellular proteinase (aeropyrolysin) from the hyperthermophilic archaeon Aeropyrum pernix K1

An extracellular metalloproteinase, which we had designated aeropyrolysin, from the aerobic marine hyperthermophilic archaeon Aeropyrum pernix K1 (JCM 9820), was purified by ammonium sulfate precipitation, anionic exchange chromatography, and gel filtration chromatography. The purified enzyme was composed of a single polypeptide chain with a molecular mass of 52 kDa as determined by SDS-PAGE. The proteinase had a broad pH optimum (pH 5-9) with a maximal activity at pH 6-8 for azocasein hydrolysis. The optimum temperature for enzyme activity was 100 degrees C in the absence of 1 mM CaCl2 and 110 degrees C in the presence of 1 mM CaCl2. The enzyme activity was completely inhibited by EDTA and EGTA, indicating that it was a metalloproteinase. The enzyme was highly resistant to the denaturing reagents urea, guanidine-HCl, dithiothreitol, 2-mercaptoethanol and SDS. The enzyme also showed a high activity with the metalloproteinase specific substrate MOCAc-Pro-Leu-Gly-Leu-A2pr(Dnp)-Ala-Arg-NH2. The enzyme was extremely thermostable showing half-lives of 2.5 h at 120 degrees C and 1.2 h at 125 degrees C in the presence of 1 mM CaCl2. These results indicate that this enzyme is one of the most thermostable extracellular proteinases reported to date.

Extremely thermostable phosphoenolpyruvate carboxylase from an extreme thermophile, Rhodothermus obamensis

Phosphoenolpyruvate carboxylase (PEPC) was purified from an extremely thermophilic bacterium, Rhodothermus obamensis, growing optimally at 80 degrees C, which had recently been isolated from a shallow marine hydrothermal vent in Japan. The native enzyme was a homotetramer of 400 kDa in molecular mass, as estimated by gel filtration chromatography, and the subunit exhibited an apparent molecular mass of 100 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The optimum temperature for enzyme activity was 75 degrees C. The enzyme exhibited an absolute requirement for divalent cations and a pH optimum of 8.0. The enzyme was extremely thermostable and there was no loss of enzyme activity on incubation for 2 h at 85 degrees C. The enzyme exhibited a positive allosteric property with acetyl-CoA and fructose 1,6-bisphosphate, and a negative one with L-aspartate and L-malate. These effectors affected not only the thermophilicity but also the thermostability of the enzyme, and the substrate, co-factors, and salts increased the thermostability as well. The extrinsic thermostabilization might be a possible mechanism for adaptation of the enzyme to high temperature.

Purification, properties, and N-terminal amino acid sequences of guar gum-degrading enzyme from Bacillus circulans K-1

A guar gum-degrading enzyme of the newly isolated Bacillus circulans K-1 was purified to an electrophoretically homogeneous state. The molecular weight of the purified enzyme was 62,000 by SDS-PAGE. The purified enzyme was separated into a least six isozymes by isoelectric focusing and the pI of these isozymes were 5.4, 5.5, 5.6, 5.8, 6.0, and 6.2, respectively. The N-terminal amino acid sequences of the typical three of these proteins were all the same, Ala-Ser-Gly-Phe-Tyr-Val-Ser-Gly-Thr-Lys-Leu-Asp-Ala-Thr-Gly-Gln-Pro-Phe- Val- Met-Arg. The enzyme was most active at pH 6.9 and at 64 degrees C. The enzyme was activated slightly by Al3+ and inhibited strongly by Sn2+ and Zn2+, N-bromosuccinimide, 2-mercaptoethanol, and ethylenediamine-tetraacetic acid.

Comparison of two-photon excitation laser scanning microscopy with UV-confocal laser scanning microscopy in three-dimensional calcium imaging using the fluorescence indicator Indo-1

Two-photon excitation laser scanning fluorescence microscopy (2p-LSM) was compared with UV-excitation confocal laser scanning fluorescence microscopy (UV-CLSM) in terms of three-dimensional (3-D) calcium imaging of living cells in culture. Indo-1 was used as a calcium indicator. Since the excitation volume is more limited and excitation wavelengths are longer in 2p-LSM than in UV-CLSM, 2p-LSM exhibited several advantages over UV-CLSM: (1) a lower level of background signal by a factor of 6-17, which enhances the contrast by a factor of 6-21: (2) a lower rate of photobleaching by a factor of 2-4; (3) slightly lower phototoxicity. When 3-D images were repeatedly acquired, the calcium concentration determined by UV-CLSM depended strongly on the number of data acquisitions and the nuclear regions falsely exhibited low calcium concentrations. probably due to an interplay of different levels of photobleaching of Indo-1 and autofluorescence, while the calcium concentration evaluated by 2p-LSM was stable and homogeneous throughout the cytoplasm. The spatial resolution of 2p-LSM was worse by 10% in the focal plane and by 30% along the optical axis due to the longer excitation wavelength. This disadvantage can be overcome by the addition of a confocal pinhole (two-photon excitation confocal laser scanning fluorescence microscopy), which made the resolution similar to that in UV-CLSM. These results indicate that 2p-LSM is preferable for repeated 3-D reconstruction of calcium concentration in living cells. In UV-CLSM, 0.18-mW laser power with a 2.6-phi pinhole (in normalized optical coordinate) gives better signal-to-noise ratio, contrast and resolution than 0.09-mW laser power with a 4.9-phi pinhole. However, since the damage to cells and the rate of photobleaching is substantially greater under the former condition, it is not suitable for repeated acquisition of 3-D images.

Rhodothermus obamensis sp. nov., a modern lineage of extremely thermophilic marine bacteria

A novel extremely thermophilic bacterium was isolated from a shallow marine hydrothermal vent environment (depth, 22 m) in Tachibana Bay, Nagasaki Prefecture, Japan. The cells of this organism were gram-negative rods. Growth occurred at temperatures between 50 and 85 degrees C (optimum temperature, 80 degrees C; doubling time at optimum temperature, 90 min), at pH 5.5 and 9.0 (optimum pH, 7.0), and in the presence of 1 and 5% NaCl (optimum NaCl concentration, 3%). The new isolate was an aerobic heterotroph which utilized the following compounds as sole energy and carbon sources: yeast extract, peptone, starch, casein, Casamino Acids, a variety of sugars, some carboxylic acids, and amino acids. As determined by a sequence analysis of the 16S rRNA, the new isolate belongs to the genus Rhodothermus and represents a modern lineage of extreme thermophiles within the domain Bacteria. On the basis of the physiological and molecular properties of the new isolate, we describe a new species, Rhodothermus obamensis. The type strain of R. obamensis is strain OKD7 (= JCM 9785).

Aeropyrum pernix gen. nov., sp. nov., a novel aerobic hyperthermophilic archaeon growing at temperatures up to 100 degrees C

A novel aerobic hyperthermophilic archaeon was isolated from a coastal solfataric vent at Kodakara-Jima Island, Japan. The new isolate, strain K1, is the first strictly aerobic organism growing at temperatures up to 100 degrees C. It grows optimally at 90 to 95 degrees C, pH 7.0, and a salinity of 3.5%. The cells are spherical shaped and 0.8 to 1.2 microns in diameter. Various proteinaceous complex compounds served as substrates during aerobic growth. Thiosulfate stimulates growth without producing H2S. The core lipids consist solely of C25-isopranyl archaeol (glycerol diether). The G + C content of the genomic DNA is 67 mol%. Phylogenetic analysis based on 16S rRNA sequence indicates that strain K1 is a new member of Crenarchaeota. On the basis of our results, the name Aeropyrum pernix gen. nov., sp. nov. is proposed (type strain: K1; JCM 9820).

Purification and characterization of phosphoenolpyruvate carboxylase from the hyperthermophilic archaeon Methanothermus sociabilis

Phosphoenolpyruvate carboxylase (PEPC) was purified for the first time from hyperthermophilic archaeon Methanothermus sociabilis, growing autotrophically with an optimum at 88 degrees C. The optimum temperature for enzyme activity was similar to that for growth and was 85 degrees C. The native enzyme was a homotetramer of 240 kDa molecular mass and the subunit displayed an apparent molecular mass of 60 kDa. The archaeal PEPC was insensitive to various metabolites which are known as allosteric effectors for most bacterial and eucaryal counterparts. The enzyme showed extreme thermostability such that there remained 80% of the enzyme activity after incubation for 2 h at 80 degrees C. These results implied that archaeal PEPC was significantly different from bacterial and eucaryal entities.

Cell surface organization by the membrane skeleton

Single-particle tracking and laser tweezers have facilitated the observation of the mechanics of molecular interactions in the plasma membrane of living cells at the level of single (or a few) molecules at nanometer/piconewton precision. These techniques have recently revealed that the membrane skeleton provides both confining and binding effects on the movement of membrane proteins, and that it can play a pivotal role in the molecular organization of the plasma membrane, especially in the formation of special membrane domains.

Expression of a 32 kilodalton Theileria sergenti piroplasm surface protein by recombinant baculoviruses

Previous studies detected a single amino acid substitution (Ala196 to Gly196) between cDNA clones encoding a 32 kDa antigen (p32) of Theileria sergenti (Chitose stock) obtained from a persistently infected calf. In this study, 2 different recombinant baculoviruses (pAc/p32-Ala196 and pAc/p32-Gly196) were constructed for the expression of p32. Molecular masses of the polypeptides produced in Spodoptera frugiperda cells infected with the recombinant baculoviruses were the same as that of authentic p32. pAc/p32-Ala196 produced additional polypeptides, with molecular masses higher than 32 kDa, which resulted from differential N-glycosylation as revealed by endo N-glycosidase treatment. The results indicate that a single amino acid substitution may lead to a conformational change in p32 which affected post-translational modification of recombinant products.

Metabolism of oxidized glycated low-density lipoprotein in cultured bovine aortic endothelial cells

The serum concentration of glycated low-density lipoprotein (gLDL) is increased in individuals with diabetes mellitus, which may be a contributing factor to the increased incidence of atherosclerosis in this population. Given the importance of oxidized LDL (oLDL) in atherosclerosis and that vascular endothelial cells express receptors for oLDL, oxidized glycated LDL (ogLDL) was prepared in vitro and its binding and degradation by cultured bovine aortic endothelial cells were examined. Glycation of native LDL (nLDL) isolated from normal human subjects was performed by incubation with 20 mM glucose at 37 degrees C for 3 days, and ogLDL was prepared by oxidation of gLDL with 1 microM CuSO4 at 37 degrees C for 12 hours. The electrophoretic mobility and thiobarbituric acid reactive substance (TBARS) value of ogLDL were greater than those of nLDL and gLDL. Both binding and degradation of ogLDL by cultured endothelial cells also were significantly greater than for nLDL and gLDL. Degradation of nLDL by endothelial cells was completely inhibited by ogLDL, whereas degradation of acetylated LDL was not inhibited by nLDL or ogLDL. Thus, the binding and degradation of ogLDL by endothelial cells do not appear to be mediated by the scavenger receptor. Although the exact mechanism is not clear, it appears that vascular endothelial cells may play a protective role against atherosclerosis by removing potential atherogenic lipoproteins.

Secretion of insulin and glucagon by the perfused pancreas of genetically obese (fa/fa) Zucker rats and its alteration with aging

To evaluate the sequential changes in secretion of insulin and glucagon by the pancreas of Zucker fa/fa rats, we examined the secretion of these peptides by the perfused pancreas of the rats and by that of their lean littermates aged 9, 18, and 54 wks. Obese rats weighted significantly more than lean rats at all ages and had increased plasma insulin except for those at 54 wks of age. Isolated pancreas of obese rats at 9 wks showed greater insulin secretion response to glucose and arginine than that of lean rats at the same age. Insulin secretion response to arginine from pancreas of obese rats at 18 wks was also greater than that from pancreas of lean rats at 18 wks. Increased glucose concentration in the perfusion medium caused less suppression in obese rats than in lean rats. 10 mM arginine stimulation resulted in a higher secretion response in lean rats than in obese rats at 18 and 54 wks. Impairment of glucagon secretion was observed even at 54 wks of age, when the obese rats no longer had significantly increased plasma insulin. This suggested that abnormal glucagon secretion was due not only to hyperinsulinemia, but also to a possible defect in the secretory mechanism.

Barriers for lateral diffusion of transferrin receptor in the plasma membrane as characterized by receptor dragging by laser tweezers: fence versus tether

Our previous results indicated that the plasma membrane of cultured normal rat kidney fibroblastic cell is compartmentalized for diffusion of receptor molecules, and that long-range diffusion is the result of successive intercompartmental jumps (Sako, Y. and Kusumi, A. 1994. J. Cell Biol. 125:1251-1264). In the present study, we characterized the properties of intercompartmental boundaries by tagging transferrin receptor (TR) with either 210-nm-phi latex or 40-nm-phi colloidal gold particles, and by dragging the particle-TR complexes laterally along the plasma membrane using laser tweezers. Approximately 90% of the TR-particle complexes showed confined-type diffusion with a microscopic diffusion coefficient (Dmicro) of approximately 10(-9) cm2/s and could be dragged past the intercompartmental boundaries in their path by laser tweezers at a trapping force of 0.25 pN for gold-tagged TR and 0.8 pN for latex-tagged TR. At lower dragging forces between 0.05 and 0.1 pN, particle-TR complexes tended to escape from the laser trap at the boundaries, and such escape occurred in both the forward and backward directions of dragging. The average distance dragged was half of the confined distance of TR, which further indicates that particle-TR complexes escape at the compartment boundaries. Since variation in the particle size (40 and 210 nm, the particles are on the extracellular surface of the plasma membrane) hardly affects the diffusion rate and behavior of the particle-TR complexes at the compartment boundaries, and since treatment with cytochalasin D or vinblastin affects the movements of TR (Sako and Kusumi as cited above), argument has been advanced that the boundaries are present in the cytoplasmic domain. Rebound of the particle-TR complexes when they escape from the laser tweezers at the compartment boundaries suggests that the boundaries are elastic structures. These results are consistent with the proposal that the compartment boundaries consist of membrane skeleton or a membrane-associated part of the cytoskeleton (membrane skeleton fence model). Approximately 10% of TR exhibited slower diffusion (Dmicro approximately 10(-10)-10(-11) cm2/s) and binding to elastic structures.

Impaired feedback inhibition of insulin secretion by hyperinsulinemia in patients with insulinoma

By means of the euglycemic three step hyperinsulinemic clamp technique, suppression of endogenous C-peptide secretion by exogenous insulin infusion was evaluated in patients with insulinoma (n = 8) and healthy controls (n = 20). Euglycemic hyperinsulinemic clamp studies were performed with an artificial pancreas (STG-22 NIKKISO, Tokyo, Japan). Insulin (Actrapid human insulin) was infused at the rate of 1.12, 3, and 10 mU/kg/min. Plasma glucose levels were clamped at 80 mg/dl, and high insulin levels were maintained in all subjects (833 +/- 78 microU/ml at the rate of 10 mU/kg/min insulin infusion). During the clamp studies, plasma C-peptide levels in normal subjects declined from 2.0 +/- 0.2 to 0.9 +/- 0.2 ng/ml, indicating suppression of endogenous insulin secretion by exogenous insulin infusion. In patients with insulinoma, plasma C-peptide levels were 3.1 +/- 1.6 ng/ml in the basal state, and were not suppressed even during exogenous hyperinsulinemia. We concluded that the feedback inhibition of insulin secretion by exogenous insulin infusion is attenuated in patients with insulinoma, and that the hyperinsulinemic clamp technique may be a useful method for the diagnosis of insulinoma.

Sulfamethizole capsule method. A new method for assessing gastric emptying of solids

We have developed a new method that is capable of assessing gastric emptying in humans. This method is based on the rapid absorption of sulfamethizole in the upper small intestine. Sulfamethizole capsules are gelatin capsules that are filled with a solid composed of egg albumin and sulfamethizole. After subjects ingested of 15 capsules with ham and bread, blood concentrations of sulfamethizole were measured and the areas under the sulfamethizole concentration-time curve (AUC) were calculated as an index of gastric emptying. After ingestion of 99mTc-labeled sulfamethizole capsules, there was a statistically significant correlation between the percentage of radioactivity remaining in the stomach at 120 min and AUC for 120 min (r = -0.82, P < 0.01). This method yielded a reliable value for gastric emptying of a solid meal as estimated by AUC. This method can be considered safe and is easily applicable to human subjects for assessment of gastric emptying.