Correlations between the thermal stability of chloroplast (thylakoid) membranes and the composition and fluidity of their polar lipids upon acclimation of the higher plant,Nerium oleander,to growth temperature

The thermal stability of excitation transfer from pigment proteins to the Photosystem II reaction center of Nerium oleander adjusts by 10 Celsius degrees when cloned plants grown at 20°C/15°C, day/night growth temperatures are shifted to 45°C/32°C growth temperature or vice versa. Concomitant with this adjustment is a decrease in the fluidity of thylakoid membrane polar lipids as determined by spin labeling. The results are consistent with the hypothesis that there is a limiting maximum fluidity compatible with maintenance of native membrane structure and function. This limiting fluidity was about the same as for a number of other species which exhibit a range of thermal stabilities. Inversely correlated shifts in lipid fluidity and thermal stability occurred during the time course of acclimation of N. oleander to new growth temperatures. Thus, the temperature at which the limiting fluidity was reached changed during acclimation while the limiting fluidity remained constant. Although the relative proportion of the major classes of membrane polar lipids remained constant during adjustments in fluidity, large changes occured in the abundance of specific fatty acids. These changes were different for the phospho- and galacto-lipids suggesting that the fatty acid composition of these two lipid classes is regulated by different mechanisms. Comparisons between membrane lipid fluidity and fatty acid composition indicate that fluidity is not a simple linear function of fatty acid composition.     

Differentiation of New Metastatic Variants of B16 Melanoma Under Different Culture Conditions

The purpose of this study was to examine the differentiation of variant tumors of the B16 metastatic melanoma when tumors were grown serially under different culture conditions and transplanted into C57BL/6J black mice, lethal yellow A^y/a, albino c/c, and C⁺/c mutant mice. Morphological and biochemical markers of melanogenesis were examined in cells in culture and in the corresponding tumors. Cellular pigmentation was assessed in terms of the levels of DOPA and 5-S-CD and in terms of tyrosinase activity in the various cell lines and tumors. The observed change from high to low metastatic capacity, which was dependent on culture conditions, appeared to be unrelated to melanogenesis even though changes were observed in the biochemical melanotic phenotype. Overall, tumor cells from spontaneous pulmonary metastases appear to differentiate in ways that are unrelated to the instability of experimental metastatic capacity. The melanotic phenotype in albino c/c and C⁺/c mice was dependent on the phenotype of the parental tumors. A marked difference was observed between two pigmentation compartments, one of which was stable in the B16 control, while the other was unstable in YB16 and MB16 variant cells and in the tumors derived from them. It appears, therefore, that the metastatic capacity of B16 metastatic variants is changeable and is independent of the unstable melanogenic behavior. The production of metastases and the differentiation of tumors in the present experiments appeared to be related to the genetic background of the mice and the epigenetic metabolic environment of tumors and cells.     

Molecular cloning of the gene for dihydrofolate reductase from Lactobacillus casei

The Lactobacillus casei gene for dihydrofolate reductase has been cloned in Escherichia coli using the multicopy vector pBR322. A restriction map of the cloned DNA has been prepared. The cloned DNA directs the synthesis of L. casei dihydrofolate reductase in E. coli and confers trimethoprim and methotrexate resistance.     

Essential oil and terpenoids of Mikania micrantha

Twenty-seven mainly terpenoid constituents were identified in the essential oil of Mikania micrantha whole plant. Higher terpenoids present in the same plant included two kaurene derivatives and taraxasterol.     

Stabilization of rat liver lysosomes by new anti-inflammatory steroids in vitro

Steroid acid esters, synthesized by modifying the 17-ketol side chain of prednisolone, were tested for their in vitro ability to stabilize heavy mitochondrial lysosomes prepared from rat liver. Membrane stabilization was determined by assessing capability of steroids to decrease extrusion of the marker enzymes (acid phosphatase, beta-glucuronidase and aryl sulfatase) from lysosomes incubated in hypo-osmotic sucrose-Tris acetate buffer. Results indicated that prednisolone (1) significantly inhibited the lysosomal release of acid phosphatase as did the new anti-inflammatory steroid, methyl 20-dihydroprednisolonate. Methyl prednisolonate exhibited weak membrane stabilization capacities and 20-dihydroprednisolonic acid, a metabolic product of methyl 20-dihydroprednisolonate, showed virtually no membrane stabilization.     

Steroid hormone receptor studies in melanoma model systems

The Transplantable B-16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid-hormone receptors are present in animal melanomas. In the B-16 melanoma, a cytoplasmic-estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid-binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [³H]-estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [³H]-estradiol binding in cytosol yielded a single class of high-affinity binding sites; the dissociation constant is 6 × 10^?10 M. The receptor molecule is shown to be estrogen-specific by ligand competition assays. In contrast to B-16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [³H]-dexamethasone. Sucrose-gradient centrifugation of cytosol from this cell line after incubation with [³H]-dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10^?9 M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final-cell density in these cells.     

Unusual patterns of benzo[a]pyrene metabolites and DNA-benzo[a]pyrene adducts produced by human placental microsomes in vitro

Human placental microsomes were incubated with [³H]benzo[a]pyrene (BP) and Salmon sperm DNA and the resulting metabolite-nucleoside complexes resolved by Sephadex LH-20 chromatography. The metabolite pattern was analyzed by high-pressure liquid chromatography (HPLC). The incubates were also co-chromatographed with extracts obtained from incubates with rat liver microsomes and [¹⁴C]BP. Phenols, quinones and 7,8-dihydrodiol were detected in the placental incubates. Both 9,10- and 4,5-dihydrodiols were very low as compared with control rat liver samples. Placental microsomes catalyzed the binding of BP metabolites to DNA in vitro, giving rise to two main complexes which co-chromatographed with rat liver-produced peaks attributable to 7,8-diol-9,10-epoxide and 7,8-oxide and/or quinones when metabolized further. The nucleoside metabolite peaks attributable to 4,5-oxide and 9-phenol-4,5-oxide were lacking when compared with the binding pattern catalyzed by rat liver. Both the total binding and specific metabolite-nucleoside adducts in the placenta correlated with fluorometrically measured aryl hydrocarbon hydroxylase (AHH) activity and with the amount of dihydrodiol formed. The results demonstrate that both the metabolite pattern and the nucleoside-metabolite complexes formed by the placental microsomes in vitro differed greatly from those produced by rat liver microsomes. These studies also suggest that it is not possible to predict specific patterns of DNA binding from AHH measurements or even from BP metabolite patterns, especially when comparing different tissues and species.