Isolation and identification of 24-hydroxyvitamin D2 and 24,25-dihydroxyvitamin D2

The isolation and identification of two metabolites of vitamin D₂ found in mammalian and avian species are reported. They are 24-hydroxyvitamin D₂ and 24,25-dihydroxyvitamin D₂. Their existence suggests that 24-hydroxylation occurs in a sterospecific manner in the 24R position and adds further support to the theory that vitamin D₂ metabolism qualitatively parallels that of vitamin D₃.     

STRUCTURAL CHANGES IN ISOLATED LIVER MITOCHONDRIA OF RATS DURING ESSENTIAL FATTY ACID DEFICIENCY

Liver mitochondria isolated in 0.44 M sucrose from rats deficient in essential fatty acids (EFA) oxidized citrate, succinate, α-ketoglutarate, glutamate, and pyruvate at a faster rate than did mitochondria isolated from normal rats; however, the oxidation of malate, caprylate, and β-hydroxybutyrate was not significantly increased. The mitochondria from deficient rats exhibited an increased ATPase activity and extensive structural damage as revealed by electron microscope examination of thin sections. An increase in citrate oxidation and ATPase activity, together with some structural damage, could be demonstrated as early as the 4^th week in rats on a fat-free diet. Saturated fat in the diet did not prevent the change in mitochondrial structure but accelerated its appearance. Both the biochemical and structural defects could be reversed within three weeks after feeding deficient rats a source of EFA. In the presence of a phosphate acceptor the effect of EFA deficiency on substrate oxidation was largely eliminated. A trend toward a reduced efficiency of oxidative phosphorylation was noted in mitochondria from EFA-deficient rats, but significant uncoupling was found only in the case of citrate, β-hydroxybutyrate, and glutamate in the presence of malonate. Together with the increased ATPase activity, the uncoupling of phosphorylation could account for the poor respiratory control found with the deficient preparation. However, EFA deficiency was without effect on the respiration of liver slices, which supports the belief that the observed changes in oxidation and phosphorylation are an artifact resulting from damage sustained by the deficient mitochondria during their isolation.     

Global patterns in local number of insect galling species

Abstract. We evaluate a three-part hypothesis explaining why gall-inducing insect species richness is so high in scleromorphic vegetation: (1) persistence of low nutrient status scleromorphic leaves facilitates the galling habit in warm temperate latitudes; (2) favourable colonization sites for gallers result from reduced hygrothermal stress, high phenolics in the outer cortex of the gall, and reduced carnivore and fungal attack in the gall; and (3) in more mesic sites, mortality is high due to carnivore attack and invasion of galls by fungi. Over 280 samples of local species of galling herbivorous insects from fourteen countries on all continents except Antarctica revealed a strong pattern of highest richness in warm temperate latitudes, or their altitudinal equivalents. The peak of galling species richness on the latitudinal gradient from the equator into the Arctic was between 25 to 38° N or S. Galling species were particularly diverse in sclerophyllous vegetation, which commonly had greater than twelve species per local sample. In mesic, non-sclerophyllous vegetation types the number of galling species was lower with twelve or fewer species present. Many sites in sclerophyllous vegetation supported between thirteen and forty-six galling species locally, including campina islands in Amazonia, cerrado savanna in central Brazil, the Sonoran Desert in Arizona and Mexico, shrubland in Israel, fynbos in South Africa and coastal scleromorphic vegetation in Australia. At the same latitude, or its elevational equivalent, galling species richness was significantly higher in relatively xeric sites when compared to riparian or otherwise mesic habitats, even when scleromorphic vegetation dominated the mesic sites. The results were consistent with the hypothesis and extend to a more general level the patterns and predictions on the biogeography of gall-inducing insects.     

Studies on the mechanisms responsible for inhibition of experimental metastasis of B16-F10 murine melanoma by pentoxifylline

Pentoxifylline (PTX), a methylxanthine derivative widely used as a hemorheological agent in the treatment of peripheral vascular disease, was studied to unveil the mechanisms responsible for its inhibitory action on B16-F10 experimental metastasis. In vitro pretreatment of B16-F10 cells with noncytotoxic concentrations of PTX significantly inhibited their adhesion to reconstituted basement membrane Matrigel® and type IV collagen as well as the relative activity of secreted 92 kD metalloproteinase. However, PTX pretreatment of B16-F10 cells did not affect their in vitro invasiveness. Heterotypic organ adhesion assays carried out with B16-F10 cells and suspended organ tissues demonstrated that pretreatment with noncytotoxic concentrations of PTX of both, tumor cells or lung tissue, brought about a dose-dependent inhibition of melanoma cell adhesion to lung. Immunohistochemical studies using antibodies against CD31 adhesion molecule (PECAM-1) revealed that B16-F10 cells adhere to lung endothelial cells. Our results suggest that PTX may exert its inhibitory effect on tumor lodgment, and as a consequence of that on experimental metastases, through an inhibitory action on cell adhesion molecules.     

Conservation implications of the link between biodiversity and ecosystem functioning

The relationship between biodiversity and individual ecosystem processes is often asymptotic, saturating at relatively low levels, with some species contributing more strongly than others. This has cast doubt on arguments for conservation based on maintenance of the functioning of ecosystems. However, we argue that the link between biodiversity and ecosystem functioning is an important additional argument for conservation for several reasons. (1) Although species differ in importance to ecosystem processes, we do not believe that this argues for preservation of just a few species for two reasons: first, it is nearly impossible to identify all species important to the numerous systems and processes on which humans depend; second, the important species themselves may depend on an unknown number of other species in their communities. (2) Arguments for conservation based on ecosystem functioning are complementary to other utilitarian, ethical and aesthetic justifications. No single reason will convince all people or protect all species, however the combination produces a strong case for conservation of biodiversity. (3) Even if the relationship between biodiversity and ecosystem functioning is asymptotic at local spatial scales and in the short term, effects of biodiversity loss are likely to be important at larger temporal and spatial scales. (4) Initial arguments for the importance of biodiversity for ecosystem functioning were largely based on a precautionary approach (points 1-3). However, we are now moving to a scientific position based on accumulating experimental evidence. The future challenge is the integration of this scientific research with policy.     

Embryo culture and taxane production inTaxus spp

Summary We have previously shown (Flores and Sgrignoli, 1991) that immature embryos ofTaxus brevifolia andT. X media are capable of precocious germination and can grow into seedlings in vitro. The cultural and environmental parameters for embryo germination and conversion into seedlings have been optimized and extended toT. baccata andT. cuspidata. A 14-h photoperiod improved embryo germination and growth into seedlings. A pregermination cold treatment of the seeds had a positive effect on both the onset and percentage of germination. Embryos from cold-treated seeds germinated earlier and at a higher frequency than those from control seeds. Boron was necessary for embryo germination, and levels of this micronutrient were established for optimal growth and germination ofT. brevifolia andT. X media cv. Hicksii embryos. Gupta and Durzan’s medium was superior to White’s for embryo germination and root formation. Naphthaleneacetic acid stimulated root formation in embryo-derived seedlings. We also found that immature embryos could be induced to form callus with embryogenic potential. Taxol and related taxanes were detected in embryo- derived seedlings.     

Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans

Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 μM Fe²⁺ per min per FeS₂ percent pulp density for the spontaneous pyrite dissolution, 10 μM Fe²⁺ per min per mM Fe³⁺ for the indirect leaching with Fe³⁺, 90 μM O₂ per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 μM O₂ per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K_m values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K_i value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe²⁺ production from Fe³⁺ plus pyrite.     

Immunosuppression in experimental cryptococcosis in rats: Modification of macrophage functions by T suppressor cells

The influence of lymphocytes on the modulation of macrophage functions in altered immune states induced by Cryptococcus neoformans infection in rats has been investigated. In this report we observed a decrease of in vitro phagocytic activity by peritoneal cells (PC) from rats that received T suppressor cells induced by cryptococcal infection, against both the same microorganism that stimulated this suppressor population (p<0.05) and another non-pathogenic primary yeast (Candida tropicalis), (p<0.02). The microbicide function of the PC from these animals present a significant decrease in challenge by C. tropicalis (p<0.002) when compared with PC from animals transferred with T normal cells. The transference of T suppressor cells induced by cryptococcal infection in animals immunized with human serum albumin-complete Freund's adjuvant (HSA-CFA) produces a significant alteration of the phagocytosis to HSA-human red cells (HSA-HRC) when compared with the phagocytosis observed in animals that received T normal cells or the phagocytosis of normal animals (p<0.001). We could also observe that the DTH to HSA studied during 30 days was negative in rats transferred with PC sensitizated with HSA and treated with suppressor T cells, when compared with the DTH response of animals transferred with PC-HSA cocultured with normal cells (p<0.05 21st day). The data presented in this paper illustrated that following infection of rats with C. neoformans there is a change in some population of accessory cells behavior reflected by the modification of several functions, such as phagocytosis, lytic activity and antigen presentation.     

Determination of genome size of Pseudomonas aeruginosa by PFGE: analysis of restriction fragments.

Genomic DNA size was measured in three strains of Pseudomonas aeruginosa, ATCC 29260 (exotoxin A), ATCC 33467 (type I smooth) and ATCC 33468 (type 2 mucoid) by transverse alternating field electrophoresis of restriction fragments. Because of the high (67%) G + C content of Pseudomonas aeruginosa, restriction enzymes that recognize sequences with at least 4 AT base pairs were expected to be rare cutters. Eight enzymes produced fragments greater than 200 kb in size: Dral (TTT/AAA), Asnl (ATT/AAT), Hpal (GTT/AAC), AfIII (C/TTAAG), Xbal (T/CTAGA), Spel (A/CTAGT), Sspl (AAT/ATT) and Ndel (CA/TATG). All eight enzymes recognized one of three rare tetranucleotide sequences, TTAA, CTAG or ATAT. Pseudomonas aeruginosa strain 29260 has a genomic DNA size of 5573 kb. Strains 33467 and 33468 have identical restriction patterns and a possible deletion with a genomic size of 5407 kb.     

Citrate transport and metabolism in mammalian cells

Citrate, an organic trivalent anion, is a major substrate for generation of energy in most cells. It is produced in mitochondria and used either in the Krebs' cycle or released into cytoplasm through a specific mitochondrial carriers. Citrate can also be taken up from blood through different plasma membrane transporters. In the cytoplasm, citrate can be used ultimately for fatty acid synthesis, which is increased in cancer cells. Here, we review the ways in which citrate can be transported and discuss the changes in transport and metabolism that occur in cancer cells. The primary focus is on the prostate gland, which is known to produce and release large amounts of citrate during its normal secretory function. The significant changes that occur in citrate‐related metabolism and transport in prostate cancer are the second focus. This review strives to relate these mechanisms to molecular biology on the one hand and to clinical applications on the other.