Acridine-psoralen amines and their interaction with deoxyribonucleic acid

A series of novel compounds in which a 9-acridinyl nucleus is linked to a psoralen nucleus in the 5- or 8-position via polyamines was prepared and examined. Their reversible binding to DNA and their irreversible binding to DNA and DNA cross-linking upon irradiation with UV-A light were examined. It was found that they were all less efficiently photoreactive than 8-methoxypsoralen (8-MOP), both in cross-linking and photobinding to DNA, whereas the ratio between their photobinding and cross-linking was 40-400 times that of 8-MOP. Compounds in which the linker was attached to the 5-position in psoralen showed smaller cross-linking and photobinding efficiencies and larger ratios between photobinding and cross-linking than those of psoralens attached in the 8-position. This strongly indicates that the 9-substituents of the acridines are oriented toward the minor groove. Flow linear dichroism studies showed that the compounds were DNA intercalating with the acridine moiety, whereas the psoralen moiety in no case was clearly intercalating. This conclusion was further supported by viscometry which also strongly indicated monointercalation.     

Differential Effect of Phleomycin on the Infectivity of Poliovirus and Poliovirus-Induced Ribonucleic Acids

The infectivity of intact poliovirus was not affected by exposure to the antibiotic phleomycin at concentrations as high as 200 mug/ml, whereas that of the singlestranded poliovirus ribonucleic acid (RNA) was inactivated to 99% by pretreatment of the RNA with phleomycin at a concentration of 2 mug/ml. The infectivity of double and multistranded RNA was 10 times less sensitive than that of singlestranded RNA to the action of this antibiotic. Preincubation of HeLa cells for 30 min with 10 to 50 mug of phleomycin reduced the sensitivity of the cells to infection by viral RNA and intact virus, indicating that phleomycin interferes with cellular functions necessary for virus replication. When phleomycin was added to cells at different times after infection with single- or double-stranded RNA, the highest inactivation of infective centers was observed immediately after infection. With time of incubation at 37 C, the infective centers became more resistant to the action of phleomycin.     

Unimportance of counterflux in the energetics of "downhill" transport

Adam Kepes suggested that the cellular transport and hydrolysis of orthonitrophenyl-beta-d-galactopyranoside is powered by the counterflux of the d-galactose resulting from beta-galactosidase action within the cell. His explanation would rationalize the unique insensitivity of this galactoside transport to energy poisons such as azide. But contrary to the predictions of this hypothesis, (i) there is no initial large inhibition that progressively lessens as galactose is produced. This was shown with a double wavelength stopped-flow spectrophotometer developed to eliminate interference from turbidity transients. (ii) The azide sensitivity does not increase with an external concentration of galactose sufficient to reverse the thermodynamic gradient. (iii) Mutation in galactose utilization or growth on highly catabolite-repressing regimens did not increase the azide sensitivity, and induction of galactose transport and metabolism did not decrease azide sensitivity. It was found that Kepes measurements must have contained two artifacts. One is that the control rate of hydrolysis decreases with time as the dense cell suspension becomes anaerobic. The other is that azide causes turbidity changes for some time after its introduction. If the former is avoided by magnetic stirring and the latter by double wavelength spectrophotometry or controls without substrate, the inhibition is constant from the earliest time that can be measured. It is therefore concluded that energy-unstarved cells, exposed to azide, still have adequate energy reserves to couple to the downhill transport, although their potential is not adequate to drive accumulation against a concentration gradient.     

Differences in the metabolism of phospholipids depending on cell population density

Pulse-chase experiments in embryonic mouse fibroblasts at low and high cell population densities using radioactive phosphate and tritiated glycerol as precursors revealed a blocked turnover of phosphatidylinositol and a blocked biosynthesis of phosphatidylethan-olamine in densely packed cells.