Quantitation of model digestive mixtures by 13C NMR.

13C nuclear magnetic resonance (NMR) spectra were obtained at 50.3 and 100.5 MHz for methanolic and aqueous mixtures of sodium taurocholate, 1-monocapryloyl-rac-glycerol, and caprylic acid. Distortionless Enhancement by Polarization Transfer (DEPT) was used to improve spectral sensitivity and resolution, and to generate calibration curves for quantitative determinations of each lipid in methanol. Alternatively, the heights for nonoverlapping peaks in a 13C NMR spectrum acquired with inverse-gated decoupling provide reliable quantitative estimates for each component of the mixture, particularly when the data are obtained in methanol. These experiments also demonstrate the feasibility of detailed NMR structural investigations in model systems for glyceride digestion.     

Centrally acting endogenous hypotensive substances in rats subjected to endotoxic shock.

Cerebroventricular perfusate (CVP) from rats subjected to endotoxic shock was infused into the lateral ventricle of the naive rat. This procedure produced a hypotensive response in the recipient rat which could be reversed by the intravenous injection of the opioid antagonist naltrexone. The degree of endotoxemic hypotension in the donor rat was attenuated by perfusing the cerebroventricular system with mock CSF. The results suggest the existence of endogenous hypotensive substances in rat central nervous system, possibly opioid in nature, which may play a critical role in the pathogenesis of endotoxic shock.     

Genotoxicity of heated cooking oil vapors.

Epidemiological studies of lung cancer in Chinese women indicated that factors other than cigarette smoking are related to lung cancer risk. A case-control study suggested that indoor air pollution, particularly from cooking oil emissions, may be involved. Condensates of volatile emissions from rapeseed and soybean cooking oils were prepared and found to be genotoxic in short-term tests including the Salmonella mutation assay, SV50 forward-mutation assay, and sister-chromatid exchange assay, as well as the micronucleus assay in mouse bone marrow. In contrast, condensates from rapeseed oil with butylated hydroxyanisole or hydrogenated rapeseed oil were not mutagenic, implicating oxidation products as the cause for mutagenicity. Peanut oil and lard condensates were not mutagenic in any assay. The association of exposure to Chinese rapeseed cooking-oil emissions and lung-cancer risk may be related to the mutagenic component of these condensates.     

Antimutagenicity of secondary metabolites from higher plants.

Higher plants contain both mutagens and antimutagens and are susceptible to mutagenesis but screening programs for detection of antimutagenesis rarely employ higher plant systems. Short-term bacterial and mammalian tissue culture systems are the norm. Using modified screening tests for detecting antimutagenic agents, higher plants have been shown to contain a variety of structurally novel antimutagenic agents. Systematic bioassay-directed methodology resulted in the isolation in pure form and biological and chemical characterization of the responsible individual active components from various plants. The methodology in use is illustrated by the isolation of cinnamic acid, cinnamyl cinnamate and cinnamyl ricinoleate as the active constituents of the classic medicinal plant product, Styrax asiatica. The methods which may be used to reveal structure-activity relationships and to explore putative molecular modes of action are illustrated with excerpts from the same study.     

Computer, Simulated Evaluation of Possible Mechanisms for Sequestering Metal Ion Activity in Plant Vacuoles: II. Zinc

Various mechanisms have been suggested for sequestering Zn ion activity in vacuoles of Zn-tolerant plants. One of these mechanisms, complexation in the vacuole with organic acids, has received some support in the recent literature. However, the lack of experimental evidence for anticipated vacuolar compartmentation and concerning the nature of metal-ligand species occurring in the vacuole has been criticized. In this study we have used computer modeling of chemical equilibria to predict the metalligand species in vacuoles of tobacco (Nicotiana tabacum) cultured cells. Results of this thermodynamic evaluation support the conclusion that citrate in the concentration range encountered in tobacco cultured cells exposed to 300 or 2000 μm Zn has high potential for forming soluble complexes with Zn, over the entire probable range of vacuolar pH 4 to 7. Complexation of Zn with oxalate is also predicted, especially in cells exposed to high Zn levels. Malate, though the most abundant acid present, showed little potential for competing with other ligands for Zn. Overall, results suggest that vacuolar sequestration of Zn by high levels of vacuolar citrate may be a central mechanism in the accumulation of Zn in plants exposed to either low or high levels of this metal.     

Phenylpropanoid and iridoid glycosides from Pedicularis lasiophrys.

Two new compounds, pedicularioside E and F, were isolated from whole plants of Pedicularis lasiophrys, along with the four known compounds, verbascoside, cistanoside C, cistanoside D and 8-epiloganin. On the basis of spectral and chemical evidence, pedicularioside E and F were identified to be 1'-O-beta-D-(3-methoxy-4-hydroxy-beta-phenyl)-ethyl-6'-O-feruloyl- alpha-L-(2-acetyl)-rhamnosyl-(1----3')-4'-acetylglucopyranoside and shanzhisin methyl ester cellobioside, respectively.     

Triterpenoid saponins from Clinopodium polycephalum.

A new triterpenoid saponin, clinopodiside A, has been isolated from Clinopodium polycephalum. Its structure was established by spectroscopic methods and X-ray diffraction analysis as 3-O-beta-D-glucopyranosyl(1----6)-[ beta-D-glucopyranosyl (1----4)]-beta-D-glucopyranosyl-olean-11,13(18)-diene-3 beta,16 beta, 23,28-tetrol.     

Inhibition of Water Splitting Increases the Susceptibility of Photosystem II to Photoinhibition

Photosystem II (PSII)-enriched membrane particles were isolated from peas (Pisum sativum L.) and treated in several different ways to inhibit the water oxidation reactions, but not reaction center function itself, as judged by the light-induced rate of reduction of 2,6-dichlorophenol indophenol with and without the artificial electron donor, diphenyl carbazide. It was shown that such treatments increased the susceptibility of the PSII-enriched membranes to photoinhibition. This trend was further observed if 2,6-dichlorophenol indophenol was present during the illumination with photoinhibitory light. On the other hand, protection against the enhanced photoinhibition was found when the water-splitting activity was reconstituted or when the artificial electron donor diphenyl carbazide was present during the preillumination. The results indicate that irreversible photodamage occurred within the PSII reaction center as a consequence of illumination with strong light and that the rate of this damage was enhanced under conditions that are expected to give rise to a photoaccumulation of oxidizing species such as P680⁺ on the donor side of PSII. This mechanism of photoinhibitory damage occurred under both aerobic and anaerobic conditions.     

Effect of Cold Treatments on the Binding Stability of Photosystem II Extrinsic Proteins and an Associated Increase in Susceptibility to Photoinhibition

When pea plants (Pisum sativum L. cv Feltham First) are subjected to freezing conditions (−18°C) followed by a thaw to 18°C, there is a significant inhibition of water-splitting capacity judged by the rate of light-induced reduction of 2,6-dichlorophenol indophenol using isolated thylakoid membrane fragments enriched in photosystem II (PSII). The freeze-thaw-induced inhibition of water-splitting activity has been correlated with the loss of the 17- and 23-kilodalton extrinsic protein of PSII and with a weakening of the binding of the 33-kilodalton protein. There was no apparent loss of bound manganese. Addition of 10 millimolar CaCl₂, however, allowed a full recovery of the water-splitting activity of these modified PSII-enriched particles. The freeze-thaw-induced changes in the organization and functional capacity of PSII was found to increase its susceptibility to photoinhibition in agreement with the concepts presented in the accompanying paper, that oxidative damage can occur within the PSII reaction center as a consequence of extending the lifetime of P680⁺.