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Studies were undertaken on a highly metastatic hamster fibrosarcoma cell line with a view to assessing whether cells entering into apoptosis, measured by counting the number of transglutaminase mediated detergent insoluble envelopes, has any synchrony with a particular phase of the cell cycle. A double exposure of thymidine was used to block cells in early S-phase. Flow cytometry in combination with [3H]thymidine incorporation into DNA was used to assess the degree of synchrony and progression through the different phases of cell cycle. The apoptotic index was found to be at its maximum in mid-S-phase. Measurement of transglutaminase activity in each phase of the cell cycle indicated that the specific activity was also at its greatest during mid S-phase. The level of enzyme was relatively unchanged throughout the cell cycle indicating that the regulation of transglutaminase activity occurs primarily through effects on catalytic activity rather than enzyme synthesis.  相似文献   
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Previous studies have shown that Sindbis virus, an enveloped alphavirus of the togavirus group, activates the alternative complement pathway in the absence of detectable antiviral immunoglobulin. The present studies examined the role of the host-determined sialic acid content of Sindbis virus on activation of the alternative complement pathway. Purified Sindbis virus grown in baby hamster kidney (BHK-SV) and in mosquito (MOSQ-SV) cells yielded virus with 10.2 and less than 2.0 nmol sialic acid/mg viral protein, respectively. Sindbis virus deficient in sialic acid (2.0 nmol sialic/mg) was also produced by treating the BHK-SV with neuraminidase (NANase-SV). When MOSQ-SV or NANase-SV was incubated in either C4DGPS or C2DHS, each consumed significantly more C3 than did BHK-SV, indicating that the ability of Sindbis virus to activate the alternative pathway is inversely related to its sialic acid content. Studies in vivo showed that virus deficient in sialic acid (MOSQ-SV) was cleared from the blood of mice much more efficiently than was virus rich in sialic acid (BHK-SV), after i.v. inoculation. Furthermore, when animals were depleted of C3 through C9 by cobra venom factor (CoVF) treatment, no differences in the clearance of high and low sialic acid-containing viruses were observed. Thus both the activation in vitro and complement-dependent clearance in vivo are significantly affected by the host-determined sialic acid content of Sindbis virus.  相似文献   
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Previously, we demonstrated that prostaglandin D2 (PGD2), a natural product of the endoperoxide PGH2, evoked bronchoconstriction when given I.V. to dogs (PROSTAGLANDINS 13:255–269, 1977). The present investigation in anesthetized dogs demonstrated that aerosols of PGD2 (0.001–0.1%) produced concentration-dependent increases in pulmonary resistance (RL) and decreases in dynamic lung compliance (CDYN) which were short-lived and equipotent to PGF. These alterations in pulmonary mechanics were partially, yet significantly, inhibited by atropine, thereby suggesting that at least a portion of the bronchoconstriction may be cholinergically mediated. Concomitant cardiovascular depressant effects of both PGD2 and PGF aerosols were much less and more variable than their bronchopulmonary effects.These results demonstrate a potent bronchoconstrictor effect of aerosolized PGD2 in dogs. PGD2 warrants further attention as a possible mediator of the bronchospasm seen in acute, reversible airways obstruction.  相似文献   
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Solutions of cytosolic proteins from rat liver contain benzo(a)pyrene solubilizing activity capable of serving as a carrier between solid state benzo(a)pyrene and microsomal cytochrome P450. Fractionation of benzo(a)pyrene-saturated cytosolic proteins on a Sephadex G-100 column or by sucrose density gradients produced benzo(a)pyrene peaks of about 46,000 daltons and a very high molecular weight material. The protein-bound benzo(a)pyrene obtained in both peaks was oxidized rapidly by microsomes in the presence of NADPH, indicating that the benzo(a)pyrene carrier activity is capable of presenting the substrate to the cytochrome P450. Liver cytosolic proteins from rats receiving intraperitoneal injection of [14C] benzo(a)pyrene was chromatographed on a column of Sephadex G-75. Radioactivity eluted at the same positions of the chromatogram as did the carrier activities described above. These results indicate that these benzo(a)pyrene carrier proteins may have an invivo role in the metabolism of benzo(a)pyrene.  相似文献   
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Breeding choruses of Hyla crucifer and H. versicolor are loud enough to be audible to migrating birds up to at least 1 km from their source, both vertically and horizontally, provided that no large obstacles intervene. During May in south-eastern New York State sound pressure levels (A weighting) at altitudes of 200 to 965 m and slant ranges from the frogs of 225 to 1020 m varied from 28 to 52 dB SPL.  相似文献   
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