3 experimentally distinct transverse relaxation components of the water in frog sciatic nerve are obtained by Carr-Purcell-Meiboom-Gill technique. The relative weights of these components: approximately 29%; approximately 50%; approximately 21% fit well with water compartments in this tissue as revealed by previous methods.

Menadione (MD) is an effective cytotoxic drug able to produce intracellularly large amounts of superoxide anion. Quercetin (QC), a widely distributed bioflavonoid, can exert both antioxidant and pro-oxidant effects and is known to specifically inhibit cell proliferation and induce apoptosis in different cancer cell types. We have investigated the relation between delayed luminescence (DL) induced by UV-laser excitation and the effects of MD, hydrogen peroxide, and QC on apoptosis and cell cycle in human leukemia Jurkat T-cells. Treatments with 500 μM H₂O₂ and 250 μM MD for 20 min produced 66.0 ± 4.9 and 46.4 ± 8.6% apoptotic cell fractions, respectively. Long-term (24 h) pre-exposure to 5 μM, but not 0.5 μM QC enhanced apoptosis induced by MD, whereas short-term (1 h) pre-incubation with 10 μM QC offered 50% protection against H₂O₂-induced apoptosis, but potentiated apoptosis induced by MD. Since physiological levels of QC in the blood are normally less than 10 μM, these data can provide relevant information regarding the benefits of flavonoid-combined treatments of leukemia. All the three drugs exerted significant effects on DL. Our data are consistent with (1) the involvement of Complex I of the mitochondrial respiratory chain as an important source of delayed light emission on the 10 μs-10 ms scale, (2) the ability of superoxide anions to quench DL on the 100 μs-10 ms scale, probably via inhibition of reverse electron transfer at the Fe/S centers in Complex I, and (3) the relative insensitivity of DL to intracellular OH• and H₂O₂ levels.

Leaves of the C3 plant Brassica oleracea were illuminated with red and/or far-red light of different photon flux densities, with or without additional short pulses of high intensity red light, in air or in an atmosphere containing reduced levels of CO2 and/or oxygen. In the absence of CO2, far-red light increased light scattering, an indicator of the transthylakoid proton gradient, more than red light, although the red and far-red beams were balanced so as to excite Photosystem II to a comparable extent. On red background light, far-red supported a transthylakoid electrical field as indicated by the electrochromic P515 signal. Reducing the oxygen content of the gas phase increased far-red induced light scattering and caused a secondary decrease in the small light scattering signal induced by red light. CO2 inhibited the light-induced scattering responses irrespective of the mode of excitation. Short pulses of high intensity red light given to a background to red and/or far-red light induced appreciable additional light scattering after the flashes only, when CO2 levels were decreased to or below the CO2 compensation point, and when far-red background light was present. While pulse-induced light scattering increased, non-photochemical fluorescence quenching increased and F0 fluorescence decreased indicating increased radiationless dissipation of excitation energy even when the quinone acceptor QA in the reaction center of Photosystem II was largely oxidized. The observations indicate that in the presence of proper redox poising of the chloroplast electron transport chain cyclic electron transport supports a transthylakoid proton gradient which is capable of controlling Photosystem II activity. The data are discussed in relation to protection of the photosynthetic apparatus against photoinactivation.

Under conditions (0.2% C02; 1% 02) that allow high rates of photosynthesis, chlorophyll fluorescence was measured simultaneously with carbon assimilation at various light intensities in spinach (Spinacia oleracea) leaves. Using a stoichiometry of 3 ATP/C02 and the known relationship between ATP synthesis rate and driving force (ApH), we calculated the light-dependent pH gradient (ApH) In photosynthesis, the reactions of the electron transport chain which produce NADPH and ATP are tightly regulated, depending on the demand for NADPH and ATP. In leaves the adenylate system never is fully phosphorylated, nor is the NADP system ever fully reduced (1). One important component of regulation is the so-called "photosynthetic control" of electron flow by the pH gradient (ApH) across the thylakoid membrane (2, 3). When more light is absorbed than can be used for assimilation, the increased ApH restricts electron transport. Restriction is caused by a ApH-dependent increase in energy dissipation (4-6) and a ApH-dependent control of electron transfer between photosystems (PSs) II and I (7,8).Most studies of the effects of ApH on electron transport have been carried out with isolated thylakoids or chloroplasts, because it was not possible to measure ApH across the thylakoid membrane in intact leaves. Even with isolated thylakoids and chloroplasts, reliable estimates of ApH are difficult to obtain (9). No quantitative information has been available about the ApH magnitude in an intact leaf and its significance in relation to energy dissipation and control of electron transport in leaves.In this study we calculate ApH across the thylakoid membrane in intact leaves and present evidence that photosynthetic electron transport is regulated by ApH in a hexacooperative manner.MATERIALS AND METHODS Spinach (Spinacia oleracea L. cv. Polka) was grown in a greenhouse with a 10-hr day/14-hr night cycle. For ATP hydrolysis measurements, thylakoid membranes were isolated (10). The ATP hydrolysis activity of membrane-bound H+-ATPase was measured in the presence of 30% methanol (11,The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 12) and the liberated Pi was monitored by absorbance at 740 nm (13). The system used for simultaneous measurements of CO2 exchange and modulated chlorophyll (Chl) fluorescence of the leaf has been described in detail (3,14 RESULTSApH Across the Thylakoid Membrane in Intact Leaves. The basic idea of this work was to calculate ApH across the thylakoid membrane inside intact leaves from the known ATP requirement of CO2 assimilation and the known relationship between ATP synthesis and driving force. Measurements of CO2 assimilation were performed under increased CO2 concentrations (0.2%) to prevent CO2 limitation, at least at low and intermediate photon flux densities. The 02 concentration was decreased to 1% to suppress photorespiration. Under these c...

Since the administration of synthetic medicines is associated with drug resistance and undesired side effects, utilization of natural compounds could be an alternative and complementary modality to inhibit or prevent the development of tumors. Epigallocatechin 3-O-gallate (EGCG, 1), the major flavan component of green tea, and genistein (2), a soy isoflavonoid, are known to have chemopreventive and chemotherapeutic effects against cancer. This study demonstrated that both flavonoids inhibit cell proliferation, an effect enhanced under serum-free conditions. Compound 1, but not 2, induced downregulation of ErbB1 and ErbB2 in mammary and epidermoid carcinoma cells, and its inhibitory effect on cell viability was mediated by the 67 kDa laminin receptor (67LR). While 1 was superior in inducing cell death, 2 was more efficient in arresting the tumor cells in the G2/M phase. Furthermore, number and brightness analysis revealed that 1 decreased the homoclustering of a lipid raft marker, glycosylphosphatidylinositol-anchored GFP, and it also reduced the co-localization between lipid rafts and 67LR. The main conclusion made is that the primary target of 1 may be the lipid raft component of the plasma membrane followed by secondary changes in the expression of ErbB proteins. Compound 2, on the other hand, must have other unidentified targets.