Protection after x-irradiation by 1,4-dithiothreitol of two mammalian cell types in vitro

1,4-Dithiothreitol (DTT) was found to diminish the amount of chromosomal breakage in leucocyte cultures of the marsupial Potorous tridactylus and in the Don strain of Chinese hamster cells (LHI). The maximum decrease of damage in Potorous lymphocytes was to 54% of that of the irradiated cells without DTT treatment, and to 64% in the case of the Chinese hamster cells. For both cell types, it was shown that the most significant effect of DTT was due to its presence in the first 30 min post irradiation. The protective action of this sulphydryl compound occurred even when DTT was not present during irradiation but was introduced as soon as possible after the X-ray dose was delivered.     

Anthraquinone pigments from Phoma foveata Foister

1. Suitable conditions have been determined for growing the fungus Phoma foveata in culture for optimum production of pigments. 2. The pigments have been extracted and fractionated according to their solubility in aqueous bicarbonate, carbonate and alkali. 3. The carbonate- and alkali-soluble pigments have been further separated by chromatography and shown to consist of anthraquinone derivatives. 4. The alkali-soluble fraction, which comprised the bulk of the pigment, consists of pachybasin (1-hydroxy-3-methylanthraquinone; II) and chrysophanol (1,8-dihydroxy-3-methylanthraquinone; III) by comparison with authentic samples. 5. The carbonate-soluble fraction contains emodin (1,6,8-trihydroxy-3-methylanthraquinone; V) and a hitherto unrecorded pigment for which the name phomarin and the structure 1,6-dihydroxy-3-methylanthraquinone (IV) are put forward. 6. The identification of emodin and the structural determination of phomarin are based largely on their ultraviolet, visible, infrared, nuclear-magnetic-resonance and mass spectra.     

Functional cooperation between co-amplified genes promotes aggressive phenotypes of HER2-positive breast cancer

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Anion effects on in vitro sarcoplasmic reticulum function. The relationship between anions and calcium flux

Isolated sarcoplasmic reticulum vesicles exhibited different functional characteristics in the presence of zwitterionic as compared to anionic buffers. In the absence of oxalate, dicarboxylic anions (e.g. maleate, succinate) in a dose-dependent manner enhanced ATP-supported Ca2+ accumulation, the ensuing spontaneous Ca2+ release, and Ca2+-dependent ATPase activity compared to zwitterionic buffers (e.g. piperazine-N,N'-bis(2-ethanesulfonic acid) (Pipes) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) (Hepes). This was not attributed to ionic strength and osmotic effects. The additional anion-dependent Ca2+ accumulation was linked to augmented Ca2+-dependent ATPase activity, and both could be induced by the addition of anion at any time during Ca2+ accumulation as long as ATP was present. Since the initial Ca2+ accumulation rates and acyl phosphoenzyme formation were the same between the two buffer classes, and the presence of either oxalate (a Ca2+-precipitating anion) or A23187 (a Ca2+ ionophore) abolished differences in Ca2+-dependent ATPase activity between the two buffer classes, it is likely that conditions favoring high intravesicular Ca2+ concentration allow the expression of the observed effect of the anions. Initial spontaneous Ca2+ release in the presence of maleate was not caused by ATP depletion, and it was virtually absent in Pipes buffer. The rate of spontaneous release was also stimulated in a dose-dependent manner by the dicarboxylic anions, with the time of release being related to the time of anion addition and not ATP addition. A later, more rapid release phase in either maleate or Pipes buffer corresponded to ATP depletion, and could be duplicated at any time in the Ca2+ accumulation/release cycle by the addition of an ATP trap. With an ATP-regenerating system present or with very high ATP concentrations, the maximal peak Ca2+ accumulation in Pipes buffer could approach that in maleate buffer. The data suggest that dicarboxylic anions stimulate the filling of a Ca2+ compartment from which spontaneous Ca2+ release occurs.     

Spontaneous phospholipid transfer: development of a quantitative model

The effects of lipid structure on the kinetics of spontaneous transfer of a series of phosphatidylcholines have been determined. Donors, which were model-reassembled high-density lipoproteins composed of apo A-I, 1-palmitoyl-2-oleoylphosphatidylcholine, and a trace of a radiolabeled lipid, were mixed with acceptors, which were human low-density lipoproteins. Within a series of phosphatidylcholines, the addition of double bonds and methylene units, respectively, increased and decreased the rate of transfer in a predictable way. An equation that predicts the rates of transfer of a large number of diacylglycerides and phosphoglycerides from any lipoprotein has been empirically derived from these data. The transfers of phosphatidylcholines that contain superpolyunsaturated fatty acids (four or more double bonds) do not obey the derived equation, probably due to limitations on the number of conformational degrees of freedom in these lipids. The range of measured transfer halftimes extends from less than 2 h to more than 12 days. Thus, the spontaneous transfer halftimes of some (but not all) lipids are short compared to the lifetime of lipoproteins in plasma. These results suggest that some lipids transfer among lipoproteins and cells via a spontaneous mechanism while others require specific transfer factors or hydrolysis to achieve this within a physiologically significant time frame.     

Membrane Asymmetry in Isolated Canine Cardiac Sarcoplasmic Reticulum: Comparison with Skeletal Muscle Sarcoplasmic Reticulum

Cardiac sarcoplasmic reticulum (CSR), isolated from dog hearts, was shown to be asymmetric in the distribution of phospholipids across the CSR bilayer. Phosphatidylethanolamine was mostly resident in the outer leaflet, phosphatidylcholine was equally distributed across both monolayers and phosphatidylserine was found primarily in the inner monolayer. This distribution of headgroups is similar to that found in fast skeletal muscle sarcoplasmic reticulum (SSR); however, the asymmetry in CSR is not as striking as that in SSR. Phospholipids retained by the CSR calcium pump protein (CaATPase) after detergent ``stripping' were similar to those intimate to the SSR CaATPase, although the percentages of unsaturated phospholipids and plasmalogenic phospholipids are not as great as in the skeletal system. Lipids associated with the CSR CaATPase following DFDNB cross-linking showed a preference for retention of the aminophospholipids, again similar to the SSR CaATPase. Because the nonrandom distribution of membrane lipids modifies SSR function, it is likely these membrane lipids impact in situ the function of the CSR. Received: 19 December 1997/Revised: 3 April 1998