Biochemistry
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The enzyme superoxide dismutase (SOD), which catalyzes the dismutation of the superoxide radical, is present in the cytosol and mitochondria of all oxygen-respiring eukaryotes. The cytosolic form contains copper and zinc (CuZnSOD), whereas the mitochondrial form contains manganese (MnSOD). The latter protein is synthesized in the cytosol as a MnSOD precursor, containing an N-terminal mitochondrial-targeting sequence. ⋯ N-Terminal amino sequences of mitochondrial and cytosolic blue crab MnSOD differ in several positions. The MnSODs are thus encoded for by two different genes. The paradigm that all eukaryotes contain intracellular CuZnSOD and that MnSOD occurs exclusively in the mitochondria appears not to apply to a large group of marine arthropods.
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Cryptophycin 1 is a remarkably potent antiproliferative compound that shows excellent antitumor activity against mammary, colon, and pancreatic adenocarcinomas in mouse xenographs. At picomolar concentrations, cryptophycin 1 blocks cells in the G2/M phase of the cell cycle by an apparent action on microtubules. The compound binds to tubulin, inhibits microtubule polymerization, and depolymerizes preformed microtubules in vitro. ⋯ At low nanomolar concentrations, in the absence of net microtubule depolymerization, cryptophycin 1 potently stabilized microtubule dynamics. It reduced the rate and extent of microtubule shortening and growing and increased the frequency of rescue. The results suggest that cryptophycin 1 exerts its antiproliferative and antimitotic activity by binding reversibly and with high affinity to the ends of microtubules, perhaps in the form of a tubulin-cryptophycin 1 complex, resulting in the most potent suppression of microtubule dynamics yet described.
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Population studies have established that one of the common isoforms of apolipoprotein E, the apoE4, is associated with higher incidence and earlier age of onset of late onset familial Alzheimer's disease (AD), whereas apoE2 may have the opposite effect. The apoE3 and apoE4 isoforms were shown to display different binding reactivities with amyloid beta peptide (Abeta) and tau protein in vitro. On the basis of these findings, it has been proposed that the apoE isoforms may modulate positively or negatively the formation of either the neurofibrillary tangles or the amyloid deposits in the brain of patients with AD. ⋯ The isoform-specific differences in binding were temperature-dependent and are attenuated upon decrease of the temperature. The binding behavior of the monomeric apoE is different from that reported for plasma apoE3 and apoE4 or commercially available apoE3 and apoE4 preparations and similar to that described for apoE3 and apoE4 produced by human embryonic kidney (HEK-293) cells. It appears that the efficiency of binding between each of three main apoE isoforms and Abeta correlates inversely with the risk of developing late-onset familial AD and may indicate possible involvement of apoE in the binding and clearance of Abeta in vivo.
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The multidrug resistant cell line CEM/VBL300 and the parental CEM T-lymphoblastic cell line from which it was derived were used to study the accumulation of fluorescent phospholipid analogs of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS). The fluorescent analogs NBD-PC, NBD-PE, and NBD-PS and [3H]PC were delivered in liposomes prepared by ethanol injection. Fluorescence microscopy demonstrated decreased accumulation of the NBD-PC analog in the multidrug resistant cell line compared to the parental cell line. ⋯ The increased accumulation was dose dependent, and the relative potency of the reversal agents paralleled their ability to circumvent multidrug resistance. In addition, the monoclonal antibody UIC2 directed against the P-glycoprotein produced similar results. The evidence presented here suggests that PC and PE but not PS behave as substrates for human MDR1 P-glycoprotein.
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This study used 2-D agarose gel techniques to examine the effects of the DNA-strand scission enediyne C-1027 on DNA replication in SV40-infected BSC-1 cells. Replication of SV40 DNA was inhibited by C-1027 to a greater extent than was BSC-1 genomic DNA replication in infected cells. Low nanomolar concentrations (0.2-10 nM) of C-1027 affected a rapid, progressive decrease in SV40 replication activity and replication intermediates (RIs) within 15 min after drug addition. ⋯ Additionally, the reduction in bubble arc signal observed with C-1027 was prevented when elongation of nascent chains was blocked by aphidicolin. Thus, the C-1027-induced disappearance of RIs probably is related to the maturation of preformed replication molecules in the absence of initiation of new RIs. Strand damage to SV40 DNA was barely detectable at concentrations where inhibition of replication activity was nearly complete, indicating that C-1027 replication inhibition occurs in trans.