Functional magnetic resonance tomography correlates of taste perception in the human primary taste cortex.

The present study investigated the functional magnetic resonance tomography correlates of taste perception in the human primary taste cortex. There is conflicting evidence in the literature about chemotopical organization in this brain region. The topography of hemodynamic activity elicited by five taste stimuli (sweet, sour, salty, bitter and umami) was analyzed on the flattened cortical surfaces of six single subjects. A high inter-individual topographical variability had to be noted. The results showed different patterns of hemodynamic activity for the investigated tastes with some considerable overlap. However, the taste specific patterns were stable over time in each subject. Such an individual taste specific pattern was also found for the umami taste within the primary taste cortex of each subject. These results suggest that input from glutamate receptors on the tongue might be processed in an exclusive way in the primary taste cortex rather than as a combination of inputs from the classical taste receptors.

Antibodies against a peptide sequence located in the linker region of the HMG-1/2 box domains in sera from patients with juvenile rheumatoid arthritis.

OBJECTIVE: To extend our work on the mapping of B cell epitopes on nucleosomal high mobility group (HMG) proteins in the sera of patients with juvenile rheumatoid arthritis (JRA). METHODS: Seventy-seven pauciarticular-onset JRA serum samples from antinuclear antibody (ANA)-positive patients and 42 polyarticular-onset JRA patient sera found to react with HMG-2 by immunoblotting were used in this study. To identify B cell epitopes on HMG-2, recombinant HMG-2 protein fragments were used in enzyme-linked immunosorbent assay (ELISA) and in competition ELISA experiments with a set of overlapping synthetic peptides. Fine epitope mapping was achieved by oligopeptide synthesis, followed by immunoblotting. RESULTS: Pauciarticular, but not polyarticular, JRA patient sera were found to recognize a lysine-rich major epitope (KKGKKKDP), which is located in the linker region of the HMG box domains of the HMG-2 nonhistone chromosomal protein. No significant immunoreactions were observed in sera from ANA-negative JRA patients and in sera from children with nonrheumatic diseases, indicating that this epitope seems to be specific for pauciarticular-onset JRA. CONCLUSION: In addition to our previous finding that JRA sera will react with a defined epitope on HMG-17, pauciarticular JRA patient sera were also found to recognize a defined epitope on the HMG-2 protein, thus suggesting the importance of this epitope in the etiology of JRA.

Sera from JRA patients contain antibodies against a defined epitope in chromosomal protein HMG-17.

Autoantibodies against the nonhistone nucleosomal protein HMG-17 have been detected in a high percentage of ANA-positive patients with pauciarticular-onset JRA4. Here we report on the epitope mapping of the HMG-17 autoantigen with a set of overlapping and nested synthetic peptides spanning the entire amino acid sequence of the human HMG-17 protein. Competition ELISA experiments defined a proline and lysine rich octapeptide PKPEPKPK as the major epitope recognized by more than 70% of the HMG-17 positive JRA sera. Point mutations introduced in the autoimmune peptide determined the amino acid residues important for autoantibody recognition. Computer based sequence comparison shows close homology between the HMG-17 autoimmune epitope and certain infectious organisms, supporting the possibility that molecular mimicry is an important factor in the etiology of JRA.

Autoantibodies to the chromosomal protein HMG-17 in juvenile rheumatoid arthritis.

OBJECTIVE: To determine the antibody profiles in sera from patients with juvenile rheumatoid arthritis (JRA). METHODS: Immunoblotting using nuclear extracts and recombinant high-mobility group (HMG) nonhistone chromosomal proteins. RESULTS: Antibodies directed against HMG-17 were found in 47% of antinuclear antibody (ANA)-positive patients with pauciarticular-onset JRA and in 16% of ANA-positive patients with polyarticular-onset JRA. HMG-17 values of 6% and 8%, respectively, were detected in ANA-negative patients with JRA and in those with nonrheumatic diseases. CONCLUSION: There is evidence for a high prevalence of anti-HMG-17 antibodies in sera of patients with pauciarticular-onset JRA.

Autoantibodies to nonhistone chromosomal proteins HMG-1 and HMG-2 in sera of patients with juvenile rheumatoid arthritis.

IgG antibodies against the high mobility group (HMG) nonhistone chromosomal proteins HMG-1 and/or HMG-2 were detected in the sera of 49 (39%) of 126 antinuclear antibody (ANA)-positive patients with juvenile rheumatoid arthritis (JRA), by immunoblotting. Clinical diagnosis classified these patients in 2 major groups, 105 with pauciarticular-onset JRA and 21 with polyarticular-onset JRA. Anti-HMG-1 and/or anti-HMG-2 antibodies were found in 8 (25%) of 32 pauciarticular-onset JRA patients with uveitis and in 34 (47%) of 73 patients without uveitis, whereas anti-HMG-1 and/or anti-HMG-2 antibodies were found in 4 (24%) of 17 children with polyarticular-onset JRA without uveitis. Among 53 sera from ANA-negative JRA patients, 3 (6%) were positive for anti-HMG-1 and/or anti-HMG-2 antibodies, whereas no reactivity to HMG-1 or HMG-2 proteins was observed in 48 sera from age-matched children with nonrheumatic diseases.

The isocitrate dehydrogenase from cyanobacteria.

The present communication describes the properties of isocitrate dehydrogenase in crude extracts from the unicellular Anacystis nidulans and from heterocysts and vegetative cells of Nostoc muscorum and Anabaena cylindrica. The activity levels of this enzyme are much higher in heterocysts than in vegetative cells of N. muscorum and A. cylindrica. Isocitrate dehydrogenase is virtually inactive in vegetative cells of A. cylindrica. The enzyme is negatively regulated by the reduction charge and scarcely affected by oxoglutarate in the three cyanobacteria. The inhibition by ATP and ADP is competitive with respect to isocitrate and NADP+ in A. cylindrica and N. muscorum and noncompetitive in A. nidulans. Isocitrate dehydrogenase from the three cyanobacteria seems to be a hysteretic enzyme. All the experimental data suggest that the major physiological role of isocitrate and the isocitrate dehydrogenase in heterocysts is not to generate reducing equivalents for N2-fixation. Oxoglutarate formed by the enzyme reaction is likely required for the biosynthesis of glutamate inside the heterocysts. Thioredoxin preparations from spinach chloroplasts or from A. cylindrica activate isocitrate dehydrogenase from either heterocysts or vegetative cells of A. cylindrica. Activation is completed within seconds and requires dithiothreitol besides thioredoxin. The thioredoxin preparation which activates isocitrate dehydrogenase also activates NADP+-dependent malate dehydrogenase from spinach chloroplasts or heterocysts of A. cylindrica. Isocitrate dehydrogenase from A. cylindrica is deactivated by oxidized glutathione. It is speculated that isocitrate dehydrogenase and thioredoxin play a role in the differentiation of vegetative cells to heterocysts.

The pyruvate: ferredoxin oxidoreductase in heterocysts of the cyanobacterium Anabaena cylindrica.

Heterocyst preparations have been obtained which actively perform nitrogen fixation (C2H2 reduction) and contain the enzymes of glycolysis and some of the tricarboxylic acid cycle. Pyruvate: ferredoxin oxidoreductase has been unambiguously demonstrated in extracts from heterocysts by the formation of acetylcoenzyme A, CO2 and reduced methyl viologen (ferredoxin) from pyruvate, coenzyme A and oxidized methyl viologen (ferredoxin) as well as by the synthesis of pyruvate from CO2, acetylcoenzyme A and reduced methyl viologen. Pyruvate supports C2H2 reduction by isolated heterocysts, however, with lower activity than Na2S2O4 and H2. alpha-Ketoglutarate: ferredoxin oxidoreductase is absent in Anabaena cylindrica, confirming that the organism has an incomplete tricarboxylic acid cycle.

Routes of flavodoxin and ferredoxin reduction in Escherichia coli. CoA-acylating pyruvate: flavodoxin and NADPH: flavodoxin oxidoreductases participating in the activation of pyruvate formate-lyase.

Flavodoxin and ferredoxin become reduced in Escherichia coli cells by oxidoreductase reactions which use pyruvate and NADPH as electron donor substrates. The two enzymes, which are minor proteins of this organism, were measured through the reduced flavodoxin-dependent activation of pyruvate formate-lyase. The NADPH-dependent enzyme, obtained homogeneously through Procion-red affinity chromatography, was identified as the flavoprotein 'component R' described previously by Fujii and Huennekens [J. Biol. Chem. 249, 6745-6753 (1974)]. The pyruvate-dependent enzyme was identified as CoA-acetylating pyruvate:flavodoxin (ferredoxin) oxidoreductase. Its catalytic properties in the forward, reverse, and the 14CO2-pyruvate exchange reaction are reported. The dihydro form of flavodoxin was characterized as the particular species involved in the activation of pyruvate formate-lyase. The activation process still occurs with 70% of maximal efficiency when the ratio [NADPH]/([NADP] + [NADPH]) is fixed at the intracellular 'anabolic reduction charge' value of 0.45, in conjunction with the NADPH-dependent enzyme. The [2Fe-2S] ferredoxin, though being readily used as electron acceptor of both oxidoreductases and having a redox potential similar to flavodoxin, proved incompetent in mediating the activation of pyruvate formate-lyase.