Clifford Stephen Duke

Publications (22) View all

• Article: EPA risk assessment principles and practices. BOSC (board of scientific counselors) workshop, February 2-3, 2005, Washington, DC.

  Rogene F Henderson, Juarine Stewart, George P Daston, Clifford S Duke, William Farland
  Environmental Science and Pollution Research 12/2005; 12(6):388-90. · 2.65 Impact Factor
• Source

  Available from: Mary M Allen

  Article: Effect of Nitrogen Starvation on Polypeptide Composition, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase, and Thylakoid Carotenoprotein Content of Synechocystis sp. Strain PCC6308.

  C S Duke, M M Allen
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  ABSTRACT: Synechocystis sp. strain PCC6308 cells were starved for nitrogen for 5 days. The polypeptide compositions of whole cell extracts and washed membranes of nitrogen-replete and nitrogen-starved cells were compared by one- and two-dimensional electrophoresis. Immunoblotting of one-dimensional gels indicated that pelletable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was depleted in cells starved for nitrogen, while levels of soluble Rubisco were comparable in nitrogen-starved and nitrogen-replete cells. This is consistent with the hypothesis that pelletable Rubisco may serve as a nitrogen reserve in Synechocystis 6308. Other polypeptides were differentially enriched in the membrane or soluble fractions of nitrogen-replete cells or nitrogen-starved cells, suggesting nitrogen starvation may alter partitioning of polypeptides into soluble and membrane fractions. Degradation of abundant polypeptides during nitrogen starvation appeared to cause an effective magnification of less abundant polypeptides in the molecular mass range of 20 to 40 kilodaltons, as shown by two-dimensional electrophoresis. A 42-kilodalton thylakoid carotenoid protein identified by immunoblotting was conserved in membranes from nitrogen-starved cells. This may be functional for cells depleted of pigment and thus exposed to higher light levels because of decreased self-shading.
  Plant physiology 11/1990; 94(2):752-9. · 6.53 Impact Factor
• Source

  Available from: Mary M Allen

  Article: Changes in polypeptide composition of Synechocystis sp. strain 6308 phycobilisomes induced by nitrogen starvation.

  C S Duke, A Cezeaux, M M Allen
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  ABSTRACT: Phycobilisomes isolated from actively growing Synechocystis sp. strain 6308 (ATCC 27150) consist of 12 polypeptides ranging in molecular mass from 11.5 to 95 kilodaltons. The phycobilisome anchor and linker polypeptides are glycosylated. Nitrogen starvation causes the progressive loss of phycocyanin and allophycocyanin subunits with molecular masses between 16 and 20 kilodaltons and of two linker polypeptides with molecular masses of 27 and 33 kilodaltons. Nitrogen starvation also leads to enrichment of four additional polypeptides with molecular masses of 46, 53, 57, and 61 kilodaltons and a transient enrichment of 35- and 41-kilodalton polypeptides in isolated phycobilisomes. The 57-kilodalton additional polypeptide was identified by immunoblotting as the large subunit of ribulosebisphosphate carboxylase/oxygenase. Proteins with the same molecular weights as the additional polypeptides were also coisolated with the 12 phycobilisome polypeptides in the supernatant of nitrogen-replete Synechocystis thylakoid membranes extracted in high-ionic-strength buffer and washed with deionized water. These observations suggest that the additional polypeptides in phycobilisomes from nitrogen-starved cells may be soluble or loosely bound membrane proteins which associate with phycobilisomes. The composition and degree of association of phycobilisomes with soluble and adjacent membrane polypeptides appear to be highly dynamic and specifically regulated by nitrogen availability. Possible mechanisms for variation in the strength of association between phycobilisomes and other polypeptides are suggested.
  Journal of Bacteriology 05/1989; 171(4):1960-6. · 3.83 Impact Factor
• Article: Effect of temperature on nitrogen-limited growth rate and chemical composition of Ulva curvata (Ulvales: Chlorophyta)

  C. S. Duke, W. Litaker, J. Ramus
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  ABSTRACT: Ulva curvata (Kutz.) de Toni growing in shallow estuaries experiences a highly variable supply of dissolved inorganic N, which can limit growth rates. The effects of N supply variability and annual temperature and light variation on growth rates and chemical composition were assessed in plants grown in outdoor tanks supplied with running seawater and either pulsed or continuous N additions for 8 d. Environmental variables were measured every 12 h, growth rates every 2 d, and plant nitrogenous constituents every 4 d. The experiment was repeated 7 times over the course of a year. The slopes of growth rate-tissue N and growth rate-N supply plots increased with temperature and varied at periods at least as short as 2 d. Temperature explained 44% of variation in growth rate, and temperature, light, and N supply together explained 53% of variation in growth rate. N-limitation occurred only above 20C, the approximate temperature for the maximum growth rate. Growth rate and tissue N were not affected by N supply frequency. Tissue N, ribulose-bisphosphate carboxylase activity, and chlorophyll contents were correlated with each other and with environmental variables but not with growth rate. U. curvata thus does not maintain balanced growth in the strict sense, but rather stores nutrients supplied as pulses for use when they become growth-limiting. Since the relative importance of any single growth-limiting factor is highly dynamic, assessing the importance of multiple limiting factors requires longterm, high-frequency sampling of principal limiting factors and seaweed growth rates.
  Marine Biology 12/1988; 100(2):143-150. · 2.28 Impact Factor
• Chapter: Observations and Insights from the NATO Advanced Research Workshop on Warfare Ecology

  William W. Doe, Clifford S. Duke, John J. Fittipaldi
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  ABSTRACT: The authors participated in the NATO Advanced Workshop as ­designated observers, for the purpose of documenting and summarizing the content of the presentations and discussions. This chapter summarizes the participant presentations during sessions A-F as well as the outcomes of three Working Group assessments. The assessments of policy implications, research priorities, and training and education followed the workshop presentations and discussions. The assessments were intended to synthesize and frame future directions and priorities in warfare ecology. KeywordsBombardment-Climate-Conflict-Ecology-Environment-Military-Security-War-Warfare
  12/2010: pages 291-300;