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G Link

Publications and source records attributed to G Link.

At least 91 records · Page 5Linked to original sources
PubMed1989

Primary structures of Sm31/32 diagnostic proteins of Schistosoma mansoni and their identification as proteases.

We have constructed cDNA clones containing the complete nucleotide sequences coding for two highly antigenic Schistosoma mansoni adult worm proteins, Sm31 and Sm32. The predicted amino acid sequence of Sm31 shows significant homology to mouse, rat and human cathepsin B. The nucleotide sequence of Sm32 is identical to that reported by others for S. mansoni "haemoglobinase'. The different nucleotide sequences demonstrate the existence of two different proteolytic enzymes, both of which are synthesised in the form of precursor molecules. Structural homology of the schistosome cathepsin B to the mammalian ones indicates that the mature protein is processed from a propeptide. The calculated molecular weight of haemoglobinase of 47,000 suggests that post-translational processing is also involved in generating an active protease.

Amino Acid Sequence↗
PubMed1989

Structure and expression of a split chloroplast gene from mustard (Sinapis alba): ribosomal protein gene rps16 reveals unusual transcriptional features and complex RNA maturation.

The mustard chloroplast gene rps16 is split by an 887 bp group II (or III) intron. Three RNA 5' ends upstream of the rps16 coding region define both the transcription start site and two RNA processing sites. The DNA region preceding the start site contains a procaryotic-type "-10" promoter element, but not a typical "-35" element. One single RNA 3' end has been detected downstream from the rps16 coding region, but it is not in close proximity to any inverted repeat that might serve as a termination signal. Northern analysis has revealed several rps16 transcripts ranging in size from 1.6 kb to 0.5 kb. During seedling development, transcript levels show an initial increase and then remain constant without much difference between seedlings grown under light or in the dark.

Amino Acid Sequence↗
PubMed1989

Iron chelation.

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Animals↗
PubMed1989

Iron loading modifies the fatty acid composition of cultured rat myocardial cells and liposomal vesicles: effect of ascorbate and alpha-tocopherol on myocardial lipid peroxidation.

Increased generation of free radicals and accelerated lipid peroxidation are important manifestations of iron toxicity. We have studied the effect of iron loading on lipid peroxidation in cultured rat myocardial cells by direct measurement of the fatty acid composition of cellular lipids. Iron loading produced by 24-hour incubation of cultured cells with 0.36 mmol/L ferric ammonium citrate resulted in a moderate reduction in polyunsaturated fatty acids (PUFAs) such as 22:5 and 22:6. A more drastic reduction in PUFAs and an apparent reciprocal increase in the proportion of saturated fatty acids were both obtained after 24 hours of incubation of liposomal vesicles prepared from whole cell lipid extracts with iron at between pH 4.5 and pH 5.5. Reduction of 22:5 and 22:6 was first noticed at 3 hours, and undetectable levels were reached by 12 and 24 hours of incubation. Ascorbate had a biphasic effect on liposomal PUFA levels: at low concentrations (0.057 mmol/L) it enhanced the iron-induced changes in liposomal fatty acid composition, but at higher concentrations (0.57 and 5.7 mmol/L), it inhibited these changes. Unlike ascorbate, alpha-tocopherol (0.023 to 2.3 mmol/L) inhibited the iron-induced reduction in PUFAs in a dose-dependent manner, with complete inhibition of the iron effect at 2.3 mmol/L. These observations underline the particular sensitivity of PUFAs to iron-induced lipid peroxidation. They also illustrate the ability of ascorbate and alpha-tocopherol to modify iron-induced lipid peroxidation. Further studies are required to explore the possible therapeutic implications of these observations in clinical iron overload.

Animals↗
PubMed1989

Effect of iron loading on transmembrane potential, contraction, and automaticity of rat ventricular muscle cells in culture.

The effect of iron loading on membrane potential and cellular contractility was examined in cultured heart cells obtained from newborn rat ventricles exposed to ferric ammonium citrate at iron concentrations of 20, 40, and 80 micrograms/ml for 24 hours. The main functional effect of iron loading was depression of the overshoot potential. Severe arrhythmias were encountered in two of eight studies with 40 micrograms/ml iron and in two of seven studies with 80 micrograms/ml iron, but they were not found in any of the 29 control studies (p less than 0.01). Iron loading also resulted in a significant enhancement of cellular LDH release, indicating a loss of cell membrane integrity. In vitro treatment of iron-loaded cells with deferoxamine, a selective iron-chelating compound, resulted in a striking reversal of the iron-induced depression in the plateau phase of action potential, the disappearance of arrhythmias, and a reduction in LDH leakage. These favorable effects of deferoxamine lend support to the contention that the observed abnormalities following iron-loading were specific expressions of iron toxicity. Although these observations are consistent with iron-induced peroxidative damage to membrane lipid components, further studies are required in order to elucidate the nature of such a putative membrane effect of excess iron.

Animals↗
PubMed1988

Diagnostic value of ferritin in malignant pleural and peritoneal effusions.

The diagnostic usefulness of ferritin measurements in pleural and peritoneal effusions has been evaluated in 57 patients. Mean (+/- standard error [SE]) ferritin levels were 291 +/- 50 ng/ml in 24 patients with noninflammatory transudates (Group I), 942 +/- 253 in 15 patients with nonmalignant exudates (Group II), and 1805 +/- 257 in 18 patients with malignant exudates (Group III). The mean (+/- SE) ratio of effusion/serum ferritin in Groups I, II, and III was 0.7 +/- 0.1, 2.7 +/- 0.7, and 5.7 +/- 1.2, respectively. The specificity and predictive value of a ferritin ratio in excess of 1.5 in distinguishing transudates from all exudates and in distinguishing transudates from malignant exudates were both very high (94%) to 96%). In the lower range of values considerable overlap existed between ferritin ratios obtained in patients with benign versus malignant inflammatory exudates. However, very high ferritin levels (greater than 3000 ng/ml) and ferritin ratios (greater than 20:1) were only encountered in malignant exudates. These results indicate that the measurement of ferritin levels and ferritin ratios may be a useful aid in the diagnosis of malignant pleural and peritoneal effusions.

Adult↗
PubMed1988

Expression of diagnostic 31/32 kilodalton proteins of Schistosoma mansoni as fusions with bacteriophage MS2 polymerase.

An expression plasmid pEx34b was used to synthesise parts of the 31/32 kDa Schistosoma mansoni antigens as fusions with the amino terminus of the phage MS2 polymerase. Purified MS2-schistosome fusion proteins reacted specifically in an enzyme-linked immunosorbent assay with sera from S. mansoni-infected patients. The observation that the majority of human sera tested recognised schistosome-specific epitopes, but not the MS2 polymerase fragment, suggests that the fusion proteins are useful for the immunodiagnosis of schistosomiasis and might be incorporated in a serological test system based on recombinant antigens.

Animals↗
PubMed1988

Human beta-casomorphin-8 immunoreactive material in the plasma of women during pregnancy and after delivery.

A method for the extraction of human beta-casomorphin-8 immunoreactive material from human plasma and a radioimmunoassay for its determination in the plasma extracts were developed. Blood was collected from 34 men, from 35 non-pregnant women, from 35 pregnant women and from 138 women after delivery and plasma extracts were assayed for the presence of human beta-casomorphin-8 immunoreactive materials. No human beta-casomorphin-8 immunoreactive material was detected in the plasma of men or non-pregnant women, whereas such material was found in the plasma of 26 out of 35 pregnant women and in the plasma of 100 out of 138 women after parturition. Material collected from women after delivery was characterized by gel filtration and high-performance liquid chromatography (HPLC) and was found to be of different composition in various individuals; its components, one of which coeluted with human beta-casein from the HPLC column, have apparently higher molecular weights than human beta-casomorphin-8. Some of these compounds seem to be very stable against enzymatic degradation at 37 degrees C in human plasma, whereas human beta-casomorphin-8 proved to be degraded very fast under identical conditions. A physiological significance of mammary products of the beta-casomorphin type during pregnancy or after parturition is suggested.

Caseins↗
PubMed1987

The chloroplast tRNALys(UUU) gene from mustard (Sinapis alba) contains a class II intron potentially coding for a maturase-related polypeptide.

The trnK gene endocing the tRNALys(UUU) has been located on mustard (Sinapis alba) chloroplast DNA, 263 bp upstream of the psbA gene on the same strand. The nucleotide sequence of the trnK gene and its flanking regions as well as the putative transcription start and termination sites are shown. The 5' end of the transcript lies 121 bp upstream of the 5' tRNA coding region and is preceded by procaryotic-type "-10" and "-35" sequence elements, while the 3' end maps 2.77 kb downstream to a DNA region with possible stemloop secondary structure. The anticodon loop of the tRNALys is interrupted by a 2,574 bp intron containing a long open reading frame, which codes for 524 amino acids. Based on conserved stem and loop structures, this intron has characteristic features of a class II intron. A region near the carboxyl terminus of the derived polypeptide appears structurally related to maturases.

Amino Acid Sequence↗
PubMed1987

Modification of iron uptake and lipid peroxidation by hypoxia, ascorbic acid, and alpha-tocopherol in iron-loaded rat myocardial cell cultures.

The ability of ascorbic acid, alpha-tocopherol, and hypoxia to modify iron uptake, chelation, and toxicity as manifested by the generation of malonyldialdehyde (MDA) was studied in myocardial cell cultures obtained from newborn rats. Exposure to 20 micrograms/ml iron provided as 59Fe-ferric ammonium citrate in serum-free Ham F-10 culture medium resulted in the accumulation of 39% of the iron within 24 hours and a 10- to 12-fold increase in cellular MDA. Hypoxia (1% oxygen) resulted in a more than twofold increase in iron uptake but only minor changes in cellular MDA concentrations. Ascorbic acid and alpha-tocopherol (1 mg/ml) had opposing effects on iron uptake and MDA production. Ascorbic acid reduced 24-hour iron uptake by 73% (P less than 0.001) whereas alpha-tocopherol increased iron uptake by 19% (P less than 0.025). In contrast, cellular MDA after iron loading increased by 86% with the addition of ascorbate, and was reduced by 75% with alpha-tocopherol (P less than 0.001). The ratio of increase in cellular MDA relative to percent iron uptake (lipid peroxidation ratio) was 7.29 with iron loading plus ascorbate vs. 0.13 with iron loading plus alpha-tocopherol, a 56-fold difference between the two extremes. In vitro deferoxamine treatment for 3 hours resulted in a 53% reduction in the radioactive iron content of iron-loaded heart cells and a 40% reduction in MDA. Simultaneous deferoxamine and ascorbate or alpha-tocopherol treatment did not affect iron mobilization, but had a profound effect on MDA concentrations. Ascorbic acid prevented entirely the beneficial effect of deferoxamine on MDA concentrations in iron-loaded cells, whereas alpha-tocopherol potentiated the effect of deferoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Ultrastructural pathology of iron-loaded rat myocardial cells in culture.

The pathological changes induced by in-vitro iron-loading or cultured rat myocardial cells were studied. Cells were exposed to 59Fe-labelled ferric ammonium citrate for up to 24 h followed by 24-72 h chase experiment. After 24 h exposure 29% of the total cellular radioactivity was found in ferritin, 10% in non-ferritin heat supernatant and 61% in an insoluble heat-precipitable form. Mössbauer spectroscopy showed a gradual shift from intracellular iron particles less than 1.8 nm in diameter, through particles of intermediate size, to ferritin-like aggregates over 3.0 nm in diameter, reaching about 20% of total iron by 24 h. Ultrastructural studies showed premature damage such as mitochondrial abnormalities and excessive autophagocytosis. Small, 2.0-5.0 nm electron-dense cytosolic particles were noticed at 3 h of iron loading and reached maximal concentrations at 6 h. This was followed by accumulation of the small particles and of typical iron-rich ferritin cores within siderosomes. Because of the limited duration of iron loading and the high concentrations of non-transferrin inorganic iron employed, the present model is more relevant to acute than chronic iron overload. The efficient incorporation of large amounts of iron within ferritin molecules and its subsequent segregation, together with other smaller particles, within membrane-bound bodies, may represent a defence mechanism limiting iron toxicity in the face of advanced cytosiderosis.

Animals↗