Bioactive compounds produced by cyanobacteria

Cyanobacteria produce a large number of compounds with varying bioactivities. Prominent among these are toxins: hepatotoxins such as microcystins and nodularins and neurotoxins such as anatoxins and saxitoxins. Cytotoxicity to tumor cells has been demonstrated for other cyanobacterial products, including 9-deazaadenosine, dolastatin 13 and analogs. A number of compounds in cyanobacteria are inhibitors of proteases — micropeptins, cyanopeptolins, oscillapeptin, microviridin, aeruginosins- and other enzymes, while still other compounds have no recognized biological activities. In general cyclic peptides and depsipeptides are the most common structural types, but a wide variety of other types are also found: linear peptides, guanidines, phosphonates, purines and macrolides. The close similarity or identity in structures between cyanobacterial products and compounds isolated from sponges, tunicates and other marine invertebrates suggests the latter compounds may be derived from dietary or symbiotic blue-green algae.     

Photodynamic therapy for multiple skin cancers

Photodynamic therapy is a new treatment modality under trial in a number of centers for use in both early and late tumors of the aerodigestive tract, bladder, brain, and skin. The theory behind its application relies on the selective uptake by a tumor bed of a photosensitizing agent such as hematoporphyrin derivative (HPD) and subsequent exposure of the tumor-bearing area to coherent laser light of suitable frequency. Following exposure, necrosis of tumor occurs to a variable degree depending on the amount of sensitizing agent absorbed by the tumor, the wavelength of laser light applied, the depth of penetration of light into the tumor, and the quantum of light energy delivered. Lack of controlled clinical data on the use of photodynamic therapy in multiple cancers of the skin led us to perform a pilot clinical study in patients. The results of this study were poor enough for us to abandon, on ethical grounds, a planned full clinical trial of the modality. The results are presented and possible reasons for failure of the method are discussed.     

Midpoints versus endpoints: The sacrifices and benefits

On May 25–26, 2000 in Brighton (England), the third in a series of international workshops was held under the umbrella of UNEP addressing issues in Life Cycle Impact Assessment (LCIA). The workshop provided a forum for experts to discuss midpoint vs. endpoint modeling. Midpoints are considered to be links in the cause-effect chain (environmental mechanism) of an impact category, prior to the endpoints, at which characterization factors or indicators can be derived to reflect the relative importance of emissions or extractions. Common examples of midpoint characterization factors include ozone depletion potentials, global warming potentials, and photochemical ozone (smog) creation potentials. Recently, however, some methodologies have adopted characterization factors at an endpoint level in the cause-effect chain for all categories of impact (e.g., human health impacts in terms of disability adjusted life years for carcinogenicity, climate change, ozone depletion, photochemical ozone creation; or impacts in terms of changes in biodiversity, etc.). The topics addressed at this workshop included the implications of midpoint versus endpoint indicators with respect to uncertainty (parameter, model and scenario), transparency and the ability to subsequently resolve trade-offs across impact categories using weighting techniques. The workshop closed with a consensus that both midpoint and endpoint methodologies provide useful information to the decision maker, prompting the call for tools that include both in a consistent framework.     

Carotenoids of cryptophyceae

The carotenoids of selected Cryptophyceae, Rhodomonas D3 and Cryptomonas ovata, have been examined by methods including HPLC, mass spectrometry ¹H NMR and circular dichroism. $\text{3′R,6′R-}\text{Chirality}$ has been assigned to monadoxanthin from ¹H NMR and CD data; β,?-carotene possessed the common $\text{6′R-}\text{chirality}$. The quantitative distribution pattern of carotenoids in Cryptophyceae established here and previously, totalling five species' is discussed in chemosystematic context. β,?-Carotene (3–8% of total) is the major carotene, accompanied by ?,?-carotene (0.2%), β,β-carotene (0–1%) and lycopene (0-trace). Zeaxanthin (2%) was identified in C. ovate. The diacetylenic alloxanthin is the major carotenoid (70–88%), and the monoacetylenic crocoxanthin (5–15%) and monadoxanthin (0–16%) less abundant. No epoxidic or allenic carotenoids could be detected. The biosynthetic precursor of acetylenic carotenoids in this primitive algal class is discussed. The significance of Cryptophyceae in the marine food chain is commented on, using alloxanthin as an indicator.     

Do Femtonewton Forces Affect Genetic Function? A Review

Protein-Mediated DNA looping is intricately related to gene expression. Therefore any mechanical constraint that disrupts loop formation can play a significant role in gene regulation. Polymer physics models predict that less than a piconewton of force may be sufficient to prevent the formation of DNA loops. Thus, it appears that tension can act as a molecular switch that controls the much larger forces associated with the processive motion of RNA polymerase. Since RNAP can exert forces over 20 pN before it stalls, a ‘substrate tension switch’ could offer a force advantage of two orders of magnitude. Evidence for such a mechanism is seen in recent in vitro micromanipulation experiments. In this article we provide new perspective on existing theory and experimental data on DNA looping in vitro and in vivo. We elaborate on the connection between tension and a variety of other intracellular mechanical constraints including sequence specific curvature and supercoiling. In the process, we emphasize that the richness and versatility of DNA mechanics opens up a whole new paradigm of gene regulation to explore.     

Effects of Liming on an Acid—Sensitive Southern Appalachian Stream

Laurel Branch (Tennessee, U.S.A.), an acid-sensitive stream in the southern Appalachian Mountains, was limed as a part of the Acid Precipitation Mitigation Program funded by the U.S. Fish and Wildlife Service. Objectives were (1) to evaluate the effectiveness of stream liming by means of a hydropowered doser design, and (2) to monitor stream response(s) to increased pH and alkalinity. Precipitation in the region was documented to be acidic, with a mean pH of 4.54 in 1987. Preliming evaluations conducted from 1986 through 1988 depicted Laurel Branch as soft (hardness less than 5 mg/L CaCO₃, pH 6.2–6.6), dilute (ionic strength less than 400 μeq/L), and lightly buffered (alkalinity less than 100 μeq/L). Because of the apparent relationship between flow and water chemistry, Laurel Branch was considered susceptible to episodic acidification caused by storms. In June 1989, a hydro–powered limestone doser was installed to treat the lower 3 km of the stream. Approximately 8.2 tonnes of crushed limestone were added during an 18–month treatment phase that concluded in December 1990. Technical and design problems with the doser reduced efficiency and limited the scale of liming through much of the first 6 months of operation. Design modifications and equipment upgrades in late 1989 corrected most of the problems and improved doser performance in 1990. No substantial chemical or biological changes were detected within the treated reach of Laurel Branch as a result of liming. Time–series statistical analyses showed small but significant changes in total alkalinity (10 μeq/L average increase) and dissolved calcium at all limed sites. pH (as hydrogen ion) increased 0.16 and 0.13 units at two limed sites that were 1 km and 2 km below the doser, respectively. At the lowermost limed site 3 km below the doser, a significant decrease in pH was detected which was probably flow-related. Mean length of age–0 (juvenile) and age-1 rainbow trout increased marginally during liming, suggesting improved fish growth, but increases were not significant. Densities of an acid-sensitive macrobenthic taxon (Baetis spp.) increased during liming, whereas densities of an acid-tolerant taxon (Leuctra spp.) remained unchanged. In general, observed biological changes were considered minimal; they were judged unrelated to liming but rather of seasonal and/or spatial origin. The regional drought of 1987 and 1988 was considered a confounding factor. With most of the baseline data collected during these years, vastly differing hydrology in 1989 and 1990 (“wet” years regionally) became problematic and may have distorted some responses and masked others. It is also possible that biological responses may have been delayed because of the small magnitude of chemical changes, particularly pH and alkalinity. A calcium mass budget estimated that up to 62% of the calcium added was accounted for in chemistry data from limed sites, with increases most visible in the spring and summer of 1990. Results indicated that, although the Laurel Branch watershed does receive acidic precipitation, current biological communities show high levels of integrity and little apparent degradation related to acidification. If watershed buffering capabilities are depleted from continued acidic deposition, however, stream biota may be at risk in the future.     

Analysis of the primary signals required for activation of the mitogenic pathway in murine thymocytes from protein phosphorylation patterns

It has been proposed that phorbol esters and the Ca2+ ionophore A23187 are effective comitogens for some species of lymphocytes because together they mimic the normal secondary signals for cell activation by mitogens that cause phosphatidylinositol 4,5-bisphosphate (PtdInsP2) breakdown (e.g., anti-TCR and anti-Thy-1 antibodies and Con A). To test whether activation of protein kinase C and an increase in [Ca2+]i account for the activation of the mitogenic pathway in murine thymocytes by the mitogens that cause PtdInsP2 breakdown, the two-dimensional phosphorylation patterns generated by the three classes of mitogens (protein kinase C activator, Ca2+ ionophore, and activator of PtdInsP2 breakdown) and by activators of cAMP-dependent kinases have been compared. From the phosphorylation patterns, by which each mitogen could be distinguished reproducibly, it was concluded that: 1) The phosphorylation patterns generated by the mitogens that activate PtdInsP2 breakdown are only slightly affected by the removal of extracellular Ca2+ under conditions that abolish the normal rise in [Ca2+]i and do not therefore depend on the activation of Ca2(+)-dependent protein kinases. In contrast, the phosphorylation pattern generated by A23187 is totally dependent on extracellular Ca2+. 2) Neither A23187 nor the mitogens that activate PtdInsP2 breakdown nor activators of cAMP-dependent kinases caused significant activation of protein kinase C assayed by phosphorylation of the diagnostic proteins 80b and 78a. Consistent with this conclusion, only the phorbol esters or oleoyl acyl glycerol caused translocation of protein kinase C activity from the cytosolic to the membrane fraction. 3) Neither A23187 nor the mitogens that cause PtdInsP2 breakdown activated cAMP-dependent kinases. Taken together the data imply that the mitogens that cause PtdInsP2 breakdown must generate an additional, independent primary mitogenic signal. It is suggested that this signal may be the activation of tyrosine kinases (e.g., p56lck) via the TCR and working hypotheses for effective combinations of primary mitogenic signals that will activate DNA synthesis are developed.