Glutathione biosynthesis in murine L5178Y lymphoma cells

The pyruvate dehydrogenase complex from pea leaf mitochondria was rapidly deactivated in the presence of 50 to 200 μm ATP. The deactivation of the complex requires Mg²⁺ as shown by EDTA inhibition of deactivation. Deactivation was inhibited by 0.1 to 1 mm pyruvate or dichloroacetate. Activation required 10 mM Mg²⁺ or Mn²⁺ but Ca²⁺ and K⁺ had no effect. Activation was inhibited by the phosphatase inhibitor, F^?. Autoradiograms of nondissociating electrophoresis gel, crossed immunoelectrophoresis gels, and dissociating sodium dodecyl sulfate electrophoresis gels of the complex showed that one protein is labeled. Labeling of this protein is prevented by Mg²⁺, pyruvate, and dichloroacetate. The pyruvate dehydrogenase complex was isolated in a partially deactivated state and reactivation required exogenous Mg²⁺ and was inhibited by F^?. These results are taken as conclusive evidence that the pyruvate dehydrogenase complex in pea leaf mitochondria undergoes interconversion between deactivated and activated states by covalent modification (phosphorylation-dephosphorylation) catalyzed by a kinase and phosphatase. Isolation of the complex in a partially deactivated (phosphorylated) state suggests a physiologically significant role for this regulatory mechanism.     

The antimutagenic effect of selenium on 7,12-dimethylbenz(a)anthracene and metabolites in the amesSalmonella/microsome system

The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene, and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na₂SeO₃ reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion. Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na₂SeO₄ inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that form and concentration are important factors in this trace element's efficacy.     

Cell patterning in branched and unbranched fruiting bodies of the cellular slime mold Polysphondylium pallidum

Cell patterning, the percentage of spores and stalk cells, was measured in branched and unbranched asexual fruiting bodies of Polysphondylium pallidum. Unlike D. discoideum, where small and large fruiting bodies are more stalky than average-sized fruiting bodies, the overall cell patterning was the same in branched and unbranched fruiting bodies of all sizes in P. pallidum. Light greatly increased the numbers of fruiting bodies in P. pallidum per unit area (or decreased aggregation territory size) so that most fruiting bodies formed in the light were small and unbranched. By contrast, light had little effect on the cell patterning of P. pallidum, although there was a slight increase in the percentage of stalk cells in the light compared to the dark. This indicates that the mechanisms governing light sensitivity of aggregation territory size and cell patterning have different components in P. pallidum. The accuracy of cell patterning of individual branches of branched fruiting bodies was so imprecise as to leave doubt that patterning is occurring at the branch level. Individual whorls of branched fruiting bodies had a greater percentage spores (90%) than whole fruiting bodies (78%) and the cell patterning was relatively imprecise. Only in whole fruiting bodies was the spore:stalk ratio highly correlated. These findings are consistent with cell pattern determination operating at the whole aggregate level, rather than at the individual whorl or branch level in P. pallidum.     

Neonatal thyroxine treatment enhances classical conditioning in the infant rat

Neonatal rats injected with either thyroxine (T₄) or vehicle (NaOH) on postnatal Days 1, 2, and 3 were given classical-conditioning pairings of an odor with footshock when 7, 9, or 11 days of age. In accord with the conventional acceleration of other indices of maturation following the T₄ treatment, 24-hr retention of the conditioned odor aversion was substantially enhanced among the 11 day-old rats given the earlier T₄ treatment. This effect was marginally significant among 9-day olds but not among 7-day olds.     

DNA methylation of liver and HTC cells during corticosteroid induction

The status of DNA methylation, as measured by m⁵C² content of nuclear DNA, was examined during corticosteroid mediated TAT induction in rat liver and in dividing and nondividing HTC cells. The m⁵C content, determined by HPLC, was not significantly altered in HTC cells during TAT induction whether the cells were in the logarithmic or stationary growth phase. In the liver of adrenalectomized rats where the range of corticosteroid effects is greater than in HTC cells, a small but significant decline in genomic levels of m⁵C was detected between 1 to 8 hr post-induction. The alterations in DNA methylation did not fluctuate during induction by more than 8% in the liver or 7.5% in HTC cells. These results demonstrate that no gross change or elevation in m⁵C content is detected in two, different, hormonally responsive hepatocellular systems during gene activation.     

A functional hybrid ribosome binding site in tryptophan operon messenger RNA of Escherichia coli

We present evidence that repair of DNA damage induced by decay of incorporated ¹²⁵I after replication of the labeled duplex of Escherichia coli requires the recA⁺ gene function. Furthermore, only about half of the cells survive after label segregation even when that repair function is present. Our results support the possibility that repair of ¹²⁵I decay-induced lesions is asymmetric, being limited to damage initiated in only one of the two strands of the DNA duplex.     

Development and differentiation of mouse blastocysts in serum-free medium

Numerous studies have shown that the in vitro development and differentiation of mouse blastocysts require serum, but the number and nature of serum factors involved remains unclear. In this article, we describe a culture medium, EM-2, containing as a source of protein only commercially purified bovine serum albumin (BSA) and fetuin. This medium supports hatching, attachment and outgrowth of mouse blastocysts. Although attachment and outgrowth are delayed in EM-2 medium 12–15 and 5–8 h, respectively, these events occur at frequencies comparable to those observed in serum-containing media. Trophoblast cells are capable of differentiating in this medium: they synthesize Δ⁵,3β-hydroxysteroid dehydrogenase and their nuclei become polyploid. The inner cell mass also appears to differentiate to some extent in EM-2 medium as evidenced by the appearance of cells with characteristics of parietal endoderm. The fetuin factor is necessary at least for trophoblast outgrowth and the albumin factor is required for the survival and/or growth of the inner cell mass. It is, however, not evident from these studies whether the serum fractions used are actually involved in the induction of differentiation, or whether the early differentiative steps in the mouse blastocyst are preprogrammed and require for expression only a normal cellular metabolic rate.     

Oocyte-follicle cell relationships in a starfish

Summary The follicle cells which surround the oocytes of starfish are known to both release the hormone 1-methyladenine and to respond to it by an active movement which forms a component of the spawning response to the hormone. In Patiria miniata these flagellated cells are located peripheral to the oocyte and have long cytoplasmic processes which penetrate the vitelline layer to the egg surface to form an adhering zonule-like junction. Within the follicle cell cytoplasm are located elongate filamentous bands which appear to represent a component of the contractile mechanism that mediates follicle cell response to 1-methyladenine. These bands do not resemble the filaments of vertebrate smooth muscle cells (quantity, distribution and size of filaments; lack of dense bodies in the filament mass), nor the contractile units of the superficial epithelium of lower vertebrate follicles.This investigation was supported by grants HD-07194 and HD-12499 from the National Institutes of Health. We are indebted to Mr. James D. Huber for able technical assistance