Influence of very low doses of ionizing radiation on Synechococcus lividus metabolism during the initial growth phase

Previous results from this laboratory have shown that very low chronic doses of gamma radiation can stimulate proliferation of the Cyanobacterium Synechococcus lividus. This modification of cell proliferation occurred during the first doubling. In this paper, we have compared the metabolism of cells cultivated in a normal environment or under chronic irradiation. Incubation of the cells in a new medium induced a high superoxide dismutase (EC 1.15.1.1, SOD) activity at the 18th hour and a degradation of phycocyanin, thus demonstrating that cells were submitted to a photooxidative stress. This increase in superoxide dismutase activity was followed by concomittant peaks of glutathione reductase (EC 1.6.4.2, GR) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6P-DH) at the 24th hour. Irradiated cultures at a dose of 53.5 mGray/year show an earlier and higher peak of SOD, GR, and G6P-DH. In a second stage, cultures showed an earlier onset of photosynthesis under irradiation, as evidenced by an increase in pigment content and an enhancement of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13, GAP-DH). These results show that the radiostimulation is related to the activation of enzymes protecting against peroxides that were induced under oxidative circumstances and to the activation of a glucose catabolism via the oxidative pentose phosphate pathway.Abbreviations mGy milli-Gray - SOD superoxide dismutase - G6P-DH glucose-6-phosphate dehydrogenase - GAP-DH glycer-aldehyde-3-phosphate dehydrogenase - GSSG oxidized glutathione     

Irreversible Activation of the Opiate Receptor of Neuroblastoma × Glioma Hybrid Cells by an Alkylating Benzomorphan Derivative

The benozomorphan derivative (-)-2-[2-(p-bromoacetamidophenyl)ethyl]-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan (BAB), capable of reacting with nucleophilic groups, acts on neuroblastoma X glioma hybrid cells as a potent, irreversible opiate agonist. Its potency in inhibiting the increase in cellular cyclic AMP, evoked by prostaglandin E1, is comparable to that of Leu-enkephalin. This also applies to its capacity to compete with [3H]D-Ala2-Met-enkephalinamide ([3H]DAEA) in binding on cell membrane preparations. The comparatively lower potency of (-)-2-[2-(p-acetamidophenyl)-ethyl]-5,9 alpha-dimethly-2'-hydroxy-5,7-benzomorphan (AB), which differs from BAB in the substitution of the bromoacetamido group by an acetamido group, is of the same order of magnitude as that of morphine. The covalent interaction of BAB with the opiate receptors is deduced from the observations that (1) it is not possible to wash away this compound from the receptors, (2) the potency of BAB in inhibiting the specific binding of [3H]DAEA increases with prolonged preincubation time, and (3) AB behaves as a reversible agonist.     

Activation of antigen-enriched B cells. II. Role of linked recognition in B cell proliferation to thymus-dependent antigens

The responsiveness to T-dependent (TD) and T-independent (TI) TNP-antigens of murine splenic B cells previously enriched for antigen-binding cells (ABC) was examined. TNP-TI antigens induced B cell proliferation. TNP-TD antigens did not induce a proliferative response regardless of the physical form or nature of the TNP-TD antigen (e.g., soluble vs particulate, low or high haptenation of carrier, TNP on various insoluble matrices, etc.). TNP-TD antigens were effective in enhancing the response of the TNP-ABC to all concentrations of lipopolysaccharide (LPS) tested, indicating that binding of antigen to surface immunoglobulin alters the LPS responsiveness of the cell. Irradiated, keyhole limpet hemocyanin- (KLH) primed T cells induced a threefold to fourfold greater B cell proliferative response with TNP-KLH than with fluoresceinated KLH (FLU-KLH) or FLU-KLH together with TNP-human serum albumin (TNP-HSA). Therefore, linked recognition appears essential for optimal T cell-mediated B cell proliferation, whereas the induction of B cell proliferation via nonlinked, carrier-activated T cells is a minor component of the response.     

The 60S ribosomal subunit is altered in the skeletal muscle of dystrophic hamsters

Polysomes from the skeletal muscle of normal and dystrophic hamsters were dissociated into ribosomal subunits by treatment with puromycin and the subunits from both strains were reassociated in all possible combinations. When their protein synthesis activity was assayed in a poly(U)-directed cell-free system at a low magnesium concentration, the reassociated ribosomes from dystrophic hamsters were less active than the ribosomes from control animals. The ribosomal defect is a property of the 60S subunit and is due to a ribosomal component rather than to abnormal binding of a non-ribosomal protein.     

Isolation and structure of nocobactin NA, a lipid-soluble iron-binding compound from Nocardia asteroides

Nocobactin NA, a lipid-soluble iron-chelating product with an unusual and characteristic u.v.-absorption spectrum, was isolated from Nocardia asteroides grown under conditions of iron deficiency. Its structure was determined by physical methods and by synthesis of one of its degradation products. Nocobactin NA was obtained as a homologous mixture of compounds with side chains of differing length, and resembles mycobactin M in structure except that it has an oxazole ring in place of an oxazoline ring, and the side chains in the cobactin fragment are considerably shorter.     

Isolation of mycobactins from various mycobacteria. The properties of mycobactins S and H

Mycobactin S has been isolated from Mycobacterium smegmatis and from Mycobacterium sp. Olitzky & Gershon, strain 2, and mycobactin H from M. thermoresistible; all three organisms were grown on synthetic media of low iron content. These two mycobactins are mixtures of compounds having the same nucleus but differing in their fatty side chains. The nucleus of mycobactin S has a chemical structure identical with that of mycobactin T but differs in the optical configuration at the beta-carbon atom of the hydroxy acid fragment; the configuration in mycobactin S is S whereas that in mycobactin T is R (the previous assignment of this configuration was incorrect). The cobactin fragment of mycobactin H is identical with that of mycobactin S, but the mycobactic acid moiety differs in having methyl groups at position 6 in the benzene ring and at position 5 in the oxazoline ring. The configurations of all the asymmetric centres have been established for both mycobactins. Improved and simplified methods for the extraction and purification of mycobactins are described.