Effects of bc1-site electron transfer inhibitors on the absorption spectra of mitochondrial cytochromes b

Changes are described that are brought about by antimycin, NoHOQnO, funiculosin, myxothiazol and mucidin in the alpha-, beta- and gamma-absorption bands of reduced and oxidized cytochromes b in the isolated complex bc1 form beef heart mitochondria. The inhibitors can be divided into 2 groups. Antimycin, funiculosin and NoHOQnO are likely to shift the spectrum of b-562 and compete for specific binding with complex bc1, with each other but not with myxothiazol and mucidin. The spectral effects of the latter two inhibitors are more difficult to interpret and may involve contributions not only from b-562 but from b-566 as well. The existence of 2 independent inhibitor binding-sites in the complex bc1 corroborates the Q-cycle hypothesis.     

Fungal origin of PBV-group viruses isolated from Penicillium brevi-compactum]

Treatment of extracts from the disintegrated mycelium of Penicillium brevi-compactum with antisera against viruses PBV-1 and PBV-3 grown on bacteria results in a considerable decrease in the infectiveness of micellar preparations toward E. coli C. This is a specific reaction since treatment with a heterologic antiserum against phage T2 has no effect on the infectiveness of the micellar extracts. The kinetics of reassociation of DNA from PBV-3 and DNA from Penicillium brevi-compactum has shown that the value of Cot at half-reassociation of these DNAs is 13.3 times higher than the value of Cot at half-reassociation of DNA from PBV-3 and heterologic DNA from chicken embryos. As was found by calculations, DNA isolated from the fungal mycelium contains virus sequences at an amount of 3.7 virus genomes per cell. These data confirm the micellar origin of the viruses PBV-1 and PBV-3. The virus PBV-3 is supposed to be present in the cells in the form of prophage.     

Effects of Suramin on PMN Interactions with Different Surfaces

Human polymorphonuclear leukocytes (PMN) were found to tightly adhere on endothelial (lines EAhy926 and ECV304) and collagen surfaces under the influence of the chemotherapeutic drug suramin. This was observed by scanning electron microscopy and quantitated by myeloperoxidase assays. Suramin also inhibited Ca²⁺ ionophore A23187-stimulated leukotriene (LT) synthesis in PMN interaction with endothelial cells or with collagen surface. Suramin decreased the release of radiolabeled arachidonic acid (AA) and 5-lip-oxygenase (5-LO) metabolites by prelabeled PMN stimulated with A23187. Using agents releasing the suramin-stimulated adhesion namely jasplakonolide and dextran sulfate, we observed a reversal of the suramin effect on leukotriene synthesis. Jasplakonolide released the adhesion of PMN on endothelial and collagen-coated surfaces and restored 5-LO activity. Dextran-sulfate released adhesion on collagen-coated surfaces and abolished suramin inhibition. Arachidonate could also overcome adhesion and inhibition of 5-LO. We conclude that suramin-induced tight attachment of PMN on to solid surfaces lead to decreased leukotriene synthesis during subsequent A23187 stimulation in the absence of exogenous substrates.     

TGFbeta2 mediates rapid inhibition of calcium influx in identified cholinergic basal forebrain neurons.

Transforming growth factors betas (TGFbetas) are known to have important roles in neuronal survival and can be upregulated in disease. However, unlike many other trophic factors, nothing is known about the rapid neurotransmitter-like actions of TGFbeta in the CNS. We explored this by examining the effects of TGFbeta on calcium influx of large enzymatically dissociated basal forebrain neurons. We show that brief application of TGFbeta2, but not TGFbeta1, to fura-2AM-loaded neurons reversibly and acutely (within seconds) inhibited K(+)-evoked calcium influx. Moreover, using single-cell RT-PCR, we confirmed that the large TGFbeta2-responsive neurons presented a cholinergic phenotype. Investigation of the signaling mechanism underlying TGFbeta2 actions using whole-cell recordings of calcium currents revealed that TGFbeta2-mediated responses were insensitive to the nonhydrolyzable GTP analogue GTPgammaS. However, TGFbeta2-mediated calcium current reductions were prevented by intracellular perfusion of a Smad2/3 peptide antagonist. Together, these results suggest that TGFbeta2 can acutely regulate the excitability of basal forebrain cholinergic neurons through an atypical signaling mechanism.