Biochemistry and molecular biology international最新文献

The association of glucocorticoid hormones receptor (GR) with heat shock protein Hsp70 in the liver cytosol of rats exposed to 41 degrees C whole body hyperthermic stress was examined by quantitative immunoblotting of the two proteins within immunopurified untransformed GR multiprotein complexes. The presence of Hsp70 in the rat liver GR heterocomplexes was confirmed, and 2-fold increase in the Hsp70 relative to the steroid binding protein content within the complexes was recorded 2 and 12 h after the stress. This increase exceeded the stress-induced elevation in the total cytoplasmic Hsp70 level, but could not be seen 24 h after the stress, when cytoplasmic Hsp70 returned to basal level. The results suggest that hyperthermic stress alters the composition of the rat liver untransformed GR heterocomplexes increasing the Hsp70 share.

Thiol groups of hemoglobin and blood glutathione are higher in Geochelone carbonaria than in Geochelone denticulata. Exposure of stripped hemolysate of both tortoises to terc-butyl hydroperoxide, resulted in a higher ferroheme oxidation of G. denticulata hemoglobin. In this example glutathione reductase and glutathione peroxidase, were not active due to the absence of GSH and NADPH, suggesting that the thiol groups of G. carbonaria hemoglobin act as antioxidant, similar to GSH. In the total hemolysate, however, where the antioxidant enzymes are active, both species showed similar levels of hemoglobin oxidation, suggesting that the protective effect of thiol groups of hemoglobin are less effective for heme protection. The activity of glutathione reductase and glutathione peroxidase was higher in erythrocytes of G. denticulata and the activity of catalase and superoxide dismutase was higher in erythrocytes of G. carbonaria.

The effects of eicosapentaenoic acid and its 15-hydroperoxy and 15-hydroxy adducts on the activity of glucosamine synthetase, the rate-limiting enzyme of mucus synthesis, in rabbit gastric antral mucosa were examined. 15-Hydroperoxy-eicosapentaenoic acid inhibited the glucosamine synthetase activity at concentrations of 10, 20 and 50 microM. The effect was concentration-dependent, and the concentration required for 50% inhibition was approximately 20 microM. Eicosapentaenoic acid and its 15-hydroxy adduct had no significant effect on the enzyme activity at the same concentration range. The experiment utilizing Fe2+ revealed that the inhibitory effect of 15-hydroperoxyeicosapentaenoic acid on the glucosamine synthetase activity is not due to hydroxy radical which is expected to be formed from the hydroperoxy adduct. These results suggest that 15-hydroperoxyeicosapentaenoic acid has the potential to reduce the synthesis of gastric mucus by inhibiting the glucosamine synthetase activity.

In order to evaluate the role of the submandibular gland (SMG) on testosterone (T) production by the testis, primary cultured testicular cells were prepared from rats that had the submandibular gland surgically ablated (G-) and control (sham operated) rats (S.O.) respectively. The cells were incubated with or without 100 ng/ml luteinizing hormone (LH) and/or SMG extract. The same linear increase in T secretion was shown by both S.O. and G- cells on multi-stimulation with LH for up to 96 hrs. However, while an equivalent response was shown for S.O. cells after a single LH stimulation at 96 hrs, T secretion by the G- cells reached a plateau after 24 hrs. The level at 96 hrs was thus approximate 30% and 33% of those of S.O. cells with and without multi-stimulus by LH for 96 hrs, respectively. When S.O. cells were cultured with SMG extract, LH-stimulated T secretion was dose-dependently inhibited and there was no effect on basal T secretion. The inhibitory effect was abolished by treatment at 95 degrees C for 5 min. Ultra-filtration indicated that the molecular size of the inhibitory agent was greater than 30,000. It is proposed that SMG may contain a high molecular weight, heat labile soluble factor(s) which affects T secretion by inhibiting LH action in testicular cells.

Insulin action on nuclear PI3-Kinase and IRS-1 was explored in HepG2 cells. Following insulin treatment, the cells were subjected to subcellular fractionation. Western blot analyses were carried out to identify IRS-1 and PI3-Kinase in the nuclear and postnuclear preparations. IRS-1 protein was identified in the nucleus under basal condition. Insulin had no effect in the content of nuclear IRS-1. In contrast, PI3-Kinase was not detected under basal condition. However, insulin treatment for 1 to 10 min caused significant increase of PI3-Kinase in the nucleus while it induced corresponding decrease of PI3-Kinase in cytoplasm. Strikingly, Insulin stimulated the association of IRS-1 and PI3-Kinase in the nucleus in a similar kinetics with the nuclear translocation of PI3-Kinase. These results suggest that insulin induces nuclear translocation of PI3-Kinase and the translocated PI3-Kinase associates with nuclear IRS-1. The association of IRS-1 and PI3-Kinase in the nucleus in response to insulin may play important roles in nuclear insulin actions.

This paper reports evidence that exposure of mitochondria to near-ultraviolet light inhibits electron transport, collapses the electric gradient, and increases non-specific membrane permeability to matrix solutes such as Ca2+. Membrane energization, as well as superoxide dismutase and catalase avoid membrane leakiness. Increased permeability correlates with a diminution in the titrated thiol groups. Plausibly the pore is formed through the formation of sulfhydryl bridges by the action of UV light-derived oxygen-centered free- radicals on membrane proteins.

We studied a phosphate acceptor for casein kinase II (CK-II) in chloroplasts, and found a 56 kDa protein (p56) as an acceptor, which was partially purified from the stroma of spinach chloroplasts. The N-terminal amino acid sequence of p56 was identical with that of the beta subunit of chloroplast ATP synthase (CF0CF1-ATPase). In addition, the recombinant beta subunit of CF1 was phosphorylated when the subunit was incubated with CK-II. These results suggest that the beta subunit of CF1 is a substrate protein of CK-II in the chloroplast.

Glycosphingolipids of head and neck carcinomas from six tumor-bearing patients were analyzed and compared to those of normal tissue from similar areas. The total glycosphingolipid content and the lipid-bound sialic acid were much higher in carcinomas than in normal tissue. Major neutral glycolipids were glucosylceramide, lactosylceramide, trihexosylceramide and paragloboside. Sulfatides were seen only in extracts from normal tissue which also showed a rather simple ganglioside pattern with #GM3 and GD3 as major species, whereas tumors showed additional species such as GM2 and GD2, along with a strong increase in LM1, GM1, GD1a and GT1b.

Lysosomal membrane of rat liver contains a highly glycosylated protein referred to as lamp-2. Lamp-2 occurs to a significant extent in a soluble fraction of rat liver lysosomes. The soluble form of lamp-2 (SF-lamp-2) was purified to electrophoretic homogeneity. An apparent molecular weight M(r) of SF-lamp-2 on sodium dodecy sulfate-polyacrylamide gel electrophoresis was determined to be 91,000 which is 5,000 less than that of the membranous form of lamp-2 (MF-lamp-2). SF- and MF-lamp-2 were very similar to each other in terms of sialic acid content, NH2-terminal amino acid sequence and isoelectric point. Gel filtration data indicated that native SF-lamp-2 has an M(r) = 360,000. Taken together, SF-lamp-2 forms a tetrameric structure consisting of a homogenous polypeptide lacking a membrane-spanning domain and a cytoplasmic tail near the COOH-terminus.

Properties of soluble thiamine triphosphatase (ThTPase), adenosine triphosphatase, nucleoside triphosphatase and alkaline phosphatase activities in bovine kidney were compared. ThTPase and the other phosphatases differed clearly in their pH-dependences, K(m) and molecular masses. Apparent K(m) and pH optimum for ThTPase were determined to be 45.5 microM and 8.9, respectively. Molecular mass of the enzyme was 29.1 kDa as estimated by Sephadex G-100 gel filtration. The results obtained show bovine kidney to contain a specific soluble ThTPase, this enzyme being the only one hydrolyzing low concentrations of ThTP.