"In vitro" effect of CCl4, PG and EDTA on GSH levels at different time of incubation of rat liver homogenates

During CCl4-induced lipid peroxidation GSH content in total homogenate from rat liver falls very rapidly in the first 30 min. of incubation "in vitro". CCl4 does not enhance the decrease in total glutathione (TG) during the incubation time, so GSH loss is mainly due to its oxidation to GSSG. On the contrary PG and EDTA, two substances decreasing lipid peroxidation rate, are able to decrease GSH oxidation, without affecting TG content. At 25 degrees C EDTA and PG completely prevent GSH decrease at pH 7.4, while at pH 6 PG affords only a partial prevention. At 37 degrees C both compounds are able to limit GSH decrease at a large extent. Lipid peroxidation seems to have a great importance in the kinetics of GSH decrease and GSSG formation, at least "in vitro". It is noteworthy that PG which inhibits lipid peroxidation stimulated by CCl4 is also able to limit the high GSH loss observed in the homogenates incubated in the presence of halogeno-alkane.     

Acid phosphatase from maize scutellum: Negative cooperativity suppression by glucose

Acid phosphatase purified from maize scutellum, upon acylation with succinic anhydride, still shows negative co-operativity for the hydrolysis of glucose-6-phosphate at pH 5.4. This phenomenon is abolished by glucose, for both native and succinylated enzymes, through stimulation of the initial velocities at sub-optimal substrate concentrations. However, negative co-operativity for the enzymatic hydrolysis of p-nitrophenylphosphate at pH 5.4 is suppressed only at high concentrations of glucose. Furthermore, the hydrolysis of p-nitrophenylphosphate is noncompetitively inhibited (low affinity form of the enzyme molecule) by glucose, which suggests the existence of different substrate binding sites.     

An ultrastructural study of oogenesis in a marine triclad

The ultrastructural features of oocyte differentiation were studied in the marine triclad Cercyra hastata. Oocytes at several stages of maturation, each surrounded by follicle cell projections, are present within each of the two ovaries. A pre-vitellogenic and a vitellogenic stage have been detected in the oogenesis of C. hastata. The pre-vitellogenic stage is mainly characterized by an increase in the nuclear and nucleolar volume and activity, and the appearance and development of cortical granule precursors which are elaborated by the Golgi complex. In early phases of the vitellogenic stage, intense delamination and blebbing of the nuclear envelope occurs which probably contributes to an increase in number of cytoplasmic membranes and to transfer of nuclear material to the cytoplasm. The rough endoplasmic reticulum is extensively developed and often assumes a ‘whorl’ array. Several areas of yolk precursor formation appear in the whorls. Numerous 2–5 μm protein yolk globules are subsequently formed which appear surrounded by a double membrane (cisternae of the smooth endoplasmic reticulum) and become randomly distributed throughout the cytoplasm of mature oocytes. The peripheral ooplasm is occupied by a monolayer of electron-dense cortical granules. Finally, the evolutionary significance of the autosynthetic mechanism of yolk production is discussed.     

Role of accessory cells in the induction of a secondary cytotoxic response to Moloney murine sarcoma virus-induced tumors

The role of Ia-positive accessory cells in the generation of a secondary cytotoxic response to tumor-associated antigens induced by Moloney murine sarcoma virus (M-MSV) was evaluated. Spleen cells from M-MSV-immune A.TL mice, depleted of accessory cells by anti-Iak serum plus C treatment and stimulated in secondary mixed leukocyte tumor cell culture (MLTC) with syngeneic Ia-negative A6ATL Moloney leukemic cells, failed to generate virus-specific cytotoxic T lymphocytes (CTL). CTL generation in Ia-depleted MLTC may be reconstituted by the addition of nonimmune Ia-positive spleen or peritoneal cells obtained not only from syngeneic A.TL but also from I-incompatible A.TH mice. This lack of restriction observed in accessory cell function is explained in terms of a nonspecific mechanism of CTL triggering mediated by soluble factors. In fact, IL 2 as well as supernatants obtained from I region-incompatible cultures consisting of M-MSV-immune, Ia-depleted A.TL spleen cells and A.TH Ia-positive cells, reconstituted secondary virus-specific CTL generation.     

Specific photoaffinity labeling of the digitalis binding site of the sodium and potassium ion activated adenosinetriphosphatase induced by energy transfer

A ouabain p-aminobenzenediazonium derivative with a high specific radioactivity has been synthesized from ouabain and used as a photolabel for the (sodium plus potassium)-activated adenosinetriphosphatase from Electrophorus electricus electric organ and from dog kidney. In the dark it binds reversibly to the digitalis receptor site, with binding characteristics comparable to those of ouabain. The photoactivation of the ouabain derivative to produced covalent labeling of the receptor was obtained by energy transfer from a tryptophan residue in the (Na+,K+)ATPase to the ouabain p-aminobenzenediazonium molecule bound at the active site. The great advantage of this procedure compared to previous methods is that free molecules of the photoactivatable derivative are not photodecomposed. Analysis of the photolabeled polypeptides on sodium dodecyl sulfate gel electrophoresis showed that over 90% of the total radioactivity incorporated was found in the large molecular weight alpha-chain of the kidney enzyme (Mr 93 000). The same specific labeling of the alpha-subunit was obtained with a crude microsomal fraction from Electrophorus electricus. A mild tryptic fragmentation of the subunit into two peptide fragments of Mr 58 000 and 41 000, respectively, shows that the digitalis receptor is located in the N-terminal 41 000 fragment.     

Purification and properties of two lectins from the latex of the euphorbiaceous plants Hura crepitans L. (sand-box tree) and Euphorbia characias L. (Mediterranean spurge).

1. From the latex of two members of the plant family Euphorbiaceae, Hura crepitans L. (sand-box tree) and Euphorbia characias L. (Mediterranean spurge), two lectins were purified by affinity chromatography on acid-treated Sepharose 6B followed by elution with D-galactose. 2. The lectin from E. characias is a single molecular species with Mr 80 000, made up of two identical subunits with Mr 40 000, and is a glycoprotein containing 11% carbohydrate. 3. The lectin from H. creptians appears as a mixture of three isolectins with Mr 140 000, consisting of four different subunits with Mr values 37 500, 35 500, 31 000, and 29 000. 4. Both lectins have haemagglutinating activity, with no specificity for human blood groups. The haemagglutinating activity is inhibited by D-galactose and by galactose-containing oligosaccharides. 5. The lectin from H. crepitans is mitogenic to human T-, but not to B-, lymphocytes. The latex of E. characias is mitogenic to T- and, to a lesser extent, to B-, lymphocytes, but the purified E. characias lectin has no mitogenic activity. 6. The lectin from H. crepitans, but not that from E. characias, inhibits protein synthesis by a rabbit reticulocyte lysate.     

Differential Recovery of Auxotrophs After Penicillin Enrichment in Escherichia coli

Various auxotrophs are recovered from a penicillin enrichment cycle with differing efficiencies. Reconstruction experiments indicate that, under starvation conditions in the presence of penicillin, most auxotrophs undergo some death, whereas prolineless mutants are virtually immune to penicillin-induced killing.