The role of active forms of oxygen in platelet aggregation and deaggregation

The effect of hydrogen peroxide on ADP-induced platelet aggregation in the presence of active oxygen species scavengers was studied. It was shown that the superoxide radical and singlet oxygen, alongside with hydrogen peroxide, may play a role in platelet interactions.     

Amino acid sequence of photosystem I subunit IV from the cyanobacterium Synechocystis PCC 6803

We describe here the complete amino acid sequence of photosystem I subunit IV from Synechocystis 6803. The molecular mass of 8.0 kDa is lower than in higher plants and Chlamydomonas, due to the lack of a characteristic, proline-rich, N-terminal sequence. The remaining sequence exhibits a good conservation, with a hydrophilic and strongly basic N-tenninal head followed by two hydrophobic domains. There is no possibility of classical membrane-spanning alpha helices. This component is likely to be one of the most stroma accessible subunits of photosystem I.     

Cyclic AMP regulation of Gs protein. Thyrotropin and forskolin increase the quantity of stimulatory guanine nucleotide-binding proteins in cultured thyroid follicles

This study was carried out to clarify the way in which thyrotropin (TSH) and forskolin regulate the adenylylcyclase complex in thyroid follicle cells. We examined the effects of chronic treatment of pig thyroid follicles with TSH or forskolin on the state of G proteins by (a) assaying adenylylcyclase activity, (b) analyzing the ADP-ribosylation of stimulatory G protein (Gs) by cholera toxin, and (c) quantifying the Gs subunits by Western blotting with antipeptide antibodies. Chronic exposure (18 h) of thyroid follicles to a low concentration of TSH (0.01-0.1 milliunit/ml) enhanced the subsequent response of adenylylcyclase to TSH. Higher concentration of TSH (1 milliunit/ml) induced a homologous desensitization of this response. In cells pretreated with forskolin, the TSH-stimulated adenylylcyclase activity was higher than in control cells. The forskolin-or guanosine 5'-(beta, gamma-imido) triphosphate (Gpp(NH)p)-stimulated adenylylcyclase activity was always significantly increased after chronic treatment of cells with TSH or forskolin. Treatment of cultured thyroid follicle membranes with [32P]NAD and cholera toxin resulted in labeling of the Gs alpha (45-52-kDa) component. Culturing follicles with TSH (0.001-1 milliunit/ml) or forskolin (0.01-10 microM) greatly affected the cholera toxin-mediated ADP-ribosylation of the Gs alpha subunit. Gs alpha labeling increased progressively to level off at 1 milliunit/ml TSH or 1 microM forskolin (150-200%). Gs alpha immunoreactivity was increased in parallel (200-300%). The immunoreactivity of G beta subunits in cells cultured with TSH or forskolin was also increased compared with control cells. Cycloheximide abolished the effects of TSH and forskolin on the follicles, suggesting that new protein synthesis is required. These results indicate that Gs protein subunits are up-regulated by TSH and forskolin and suggest that their synthesis in thyroid cells is mediated, at least in part, by a cyclic AMP-dependent mechanism.     

Effects of 4-methyluracil and carnosine on healing of skin wounds in rats

In experiments in vivo and in vitro the authors studied antioxidative properties of 4-methyluracil and carnosine, their capacity to inhibit sex and accelerate healing of skin wounds. 4-methyluracil and carnosine discover almost the same capacity to decrease in the tissues of the wound and the blood serum in the formation of various intermediate products of free radical oxidation. Data are given on the study of the dynamics of wound healing after a 5-day treatment with equimolar quantities.     

Two novel mutations in the MHC class II transactivator CIITA in a second patient from MHC class II deficiency complementation group A

Congenital MHC class II deficiency or bare lymphocyte syndrome (BLS; McKusick 209920) is caused by defects in trans-acting regulatory factors that control MHC class II expression and is therefore a disease of gene regulation. There are at least four complementation groups and the genetic and molecular dissection of this rare disease has contributed considerably to our current understanding of the molecular mechanisms governing MHC class II expression. Identification of the gene that is defective in BLS complementation group A, CIITA (MHC class II transactivator), has led to the discovery that CIITA acts as a master control factor of MHC class II expression. We have identified the CIITA mutations in a second patient from BLS group A. Two novel mutations abolish CIITA function, as shown by transfection experiments. Molecular analysis of these two novel mutations, together with the one described earlier in the first patient, is informative in terms of CIITA structure-function relationships. Received: 19 October 1996 / Revised: 25 November 1996     

Study of the biosynthesis of fumonisins B1, B2 and B3 by different strains of Fusarium moniliforme

The relationship between fungal growth and the production of fumonisin on maize grain by 25 strains of Fusarium moniliforme of different origins has been investigated. Although sporulation was essentially the same for all the strains (about 10⁸ propagules g⁻¹ dry matter), ergosterol assays revealed marked variations in fungal biomass. All strains studied produced highly variable amounts of fumonisin B1, the highest levels being observed in strains of ergosterol content above 400 μg g⁻¹. However, no correlation could be established between the synthesized biomass and the quantity of fumonisins produced. We verified that ergosterol is an indicator of mycelial growth, and therefore of the potential toxicity of the analysed grain.     

Kinetics of beta-tubulin exchange following translation. Evidence for a slow conformational change in beta-tubulin necessary for incorporation into heterodimers

Cell-free translation of beta-tubulin mRNA generates full length beta-tubulin polypeptides distributed in three molecular forms: a high molecular weight lysate-associated form, the free beta-tubulin subunit, and the alpha beta-heterodimer (Yaffe, M.B., Farr, G. W., and Sternlicht, H. (1988) J. Biol. Chem. 263, 16023-16031). A quantitative assay system for these three forms was developed and used to measure the rates of incorporation/exchange of the newly synthesized free beta-subunit and the high molecular weight form into tubulin heterodimers following incubation of the 35S-translation products with unlabeled bovine tubulin dimer. This exchange process was found to be slow and strongly temperature-dependent. The half-lives for exchange ranged from 12.5 min at 37 degrees C to 17.5 h at 0 degree C with a measured activation energy of 22.5 kcal/mol. Microtubule-associated proteins appeared to play no role in the exchange process, since identical exchange rates were observed regardless of whether microtubule protein or phosphocellulose-purified tubulin was used as the source of tubulin dimer. Surprisingly, the exchange rates were found to be independent of dimer concentration. We interpret these results as evidence for a rate-limiting, slow conformational change that occurs within the newly synthesized beta-subunits prior to their association with alpha-tubulin to generate the alpha beta-hetero-dimer.