Structure-activity relationships involved in the site-specific fragmentation of linear duplex DNAs by talisomycin and bleomycin analogs

The fragmentation of Hind III- and Pst I-digested PM2 DNA and of Hind III-digested pBR322 DNA by bleomycin A2 and B2 and talisomycins A, B, S2b, and S10b was investigated. As observed by electrophoresis on agarose gels, the ethidium bromide staining band patterns produced following incubation of the various restriction endonuclease-digested DNAs with the compounds were different for the bleomycin analogs and for the talisomycin analogs. Quantitation of the degree of fragmentation of various segments of linear PM2 DNA by either bleomycin A2 or talisomycin A indicated that certain segments of the PM2 genome serve as better substrates than other segments for double-strand fragmentation by either of the two antitumor antibiotics. These results show that in this system bleomycin and talisomycin analog treatment of linear PM2 or pBR322 DNA resulted in breakage of DNA, producing different-length DNA fragments, and demonstrate the importance of the two amino acids and the 4-amino-4,6-dideoxy-L-talose sugar, which are located near the bithiazole in talisomycin but absent in the bleomycin structure in conferring a different site-specificity for DNA fragmentation to talisomycin than to bleomycin.

Comparison of the sequences at specific sites on DNA cleaved by the antitumor antibiotics talisomycin and bleomycin

We have investigated the site-specific cleavage of DNA by the antitumor antibiotics talisomycin and bleomycin by using 5'- or 3'-terminal 32P-labeled restriction fragments of pBR 322 DNA. Both drugs cleaved DNA preferentially at G-C and G-T sequences. However, the relative amounts of cleavage at particular cleavage sites differed between talisomycin and bleomycin at concentrations of the drugs which produced similar extents of total cleavage. In addition, talisomycin produced specific cleavages at G-A sequences which were relatively resistant to cleavage by bleomycin. Within a preferred sequence group (i.e., G-C sequences), some sites were cleaved to a greater extent relative to others by both talisomycin and bleomycin, suggesting that a greater degree of specificity than that provided by only two nucleotides is involved in the site-specific recognition and cleavage of DNA by these drugs.

Viscometric and fluorometric studies of deoxyribonucleic acid interactions of several new anthracyclines

Interactions involved in the binding of the anthracycline analogues adriamycin, carminomycin, pyrromycin, musettamycin, marcellomycin, and aclacinomycin to calf thymus DNA and covalently closed circular PM-2 DNA have been studied. Fluorescence quenching experiments revealed that denaturation of calf thymus DNA and increasing ionic strength each resulted in a marked decrease in the DNA binding affinities of all of the anthracyclines studied. These results suggest that intercalative and electrostatic interactions are both important in the DNA binding of these analogues. Viscometric studies indicated that under high ionic strength conditions which negated electrostatic effects, all of the anthracyclines induced an unwinding--rewinding process of the closed superhelical PM-2 DNA typically observed for DNA intercalators. Relative to the 26 degrees unwinding angle of ethidium bromide, anthracyclines with a daunomycinone-like aglycon induced an unwinding angle of approximately 13 degrees. This differed slightly from the unwinding angles of 10.3 degrees-11.1 degrees which were induced by anthracyclines with a pyrromycinone-like aglycon. Increases in the length of the glycosidic side chain did not elicit significant differences in PM-2 DNA unwinding ability, implying a lack of effect of glycosidic side chain length on the anthracycline intercalation process. The unwinding angles also showed little sensitivity to decreases in ionic strength, suggesting that the fraction of bound anthracycline molecules which are in a nonintercalated state is similar to the fraction of bound ethidium bromide molecules which are in a nonintercalated state.

DNA breakage activity of the methanol extract of auromomycin

The constituents of the antitumor agent auromomycin have been analyzed to determine their DNA-breakage activities. Spectral analysis showed that the methanol extract contained 70% of the non-peptide chromophore, whereas the residue contained 20%. Amino acid analysis of the methanol extract showed that it contained 21%-26% of the original auromomycin polypeptides. The DNA-degradation activity of the extract was 121% +/- 28% of that of the untreated auromomycin, whereas that of the residue was only 22% +/- 3.8%. Mixing of the residue and the methanol extract resulted in the loss of three-fourths of the total activity. Agarose gel electrophoretic analysis showed that the single-strand DNA breakage activity of the methanol extract was 6.5-fold greater than that of the double-strand DNA-breakage activity. The difference in the total DNA-cleavage activity of the untreated, methanol-treated, and remixed auromomycin preparations may suggest the occurrence of certain non-peptide chromophore-polypeptide interactions in both the untreated and the remixed preparations. This is consistent with the fluorescent changes observed upon mixing of the extract and residue. Fractionation of the methanol extract by Sephadex chromatography revealed that several column fractions which were enriched with non-peptide chromophore relative to the polypeptides contained in them still had significant DNA-degradation activity. These studies suggest that the non-peptide chromophore in the auromomycin preparation may contribute to most of the observed DNA breakage activity.

Inhibition of bleomycin-induced DNA breakage by superoxide dismutase

Inhibition of bleomycin (BLM)-induced DNA breakage by superoxide dismutase (SOD) has been reported and presumed to be due to its removal of the superoxide free radicals generated by BLM in the presence of iron(II). We have studied the possibility that the inhibitory effect might result from DNA-binding of SOD. The effect of copper-zinc SOD on BLM-induced DNA degradation was investigated using the PM-2 DNA fluorescence technique. PM-2 DNA was incubated with BLM in the presence or absence of native and heat-inactivated copper-zinc SOD as determined by the epinephrine autoxidation method. The concentrations of SOD required to inhibit 50% PM-2 DNA degradation for the native and the inactivated SOD were 100 and 120 microgram/ml, respectively. Analysis of the reaction mixture by agarose gel electrophoresis confirmed the absence of DNA degradation by BLM in the presence of either form of SOD. PM-2 DNA was shown to bind native or inactivated SOD by Sephadex G-100 column chromatography, fluorescence-quenching studies, and agarose gel electrophoresis. Thus, these results indicate that SOD is able to bind to PM-2 DNA and inhibit BLM-induced degradation independently of its free radical-scavenging activity. The inhibitor was more effective against BLM than other compounds which degrade PM-2 DNA. This suggests that SOD may bind to BLM-binding and/or BLM degradation sites in PM-2 DNA, and the observed inhibition is unrelated to its effects on free radicals.

[DNP-peptidase activity in the rabbit ovary (author's transl)]

To examine the possible roles of collagenolytic enzymes in the follicular wall at ovulation, we measured in rabbit ovaries collagenolytic enzymes by using synthetic substrates, DNP-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg OH supposed to be specific for vertebrate collagenase. Our results clearly demonstrated that DNP-peptidase activity existed, with its optimal pH7.6-pH7.8 in rabbit ovarian follicles. DNP-peptidase activity steadily increased for nine hours following the hCG injection. After nine hours of enzyme activity decreased sharply until about the tenth hour, at which time ovulation had occurred. This pattern of enzyme activities indicates that the DNP-peptidase was consumed for degradation of collagen fibers. After collagen fibers have been completely degraded, this enzyme was increased again. These changes of DNP-peptidase activities at ovulation were similar to cathepsin B1 activities with its optimal pH6.0. It is concluded that DNP-peptidase could be one of ovulatory enzymes in the rabbit.

Single-strand and double-strand deoxyribonucleic acid breaks produced by several bleomycin analogues

Production of single-strand breaks (ssb) and double-strand breaks (dsb) of PM2 phage DNA by several structurally related bleomycin (BLM) analogues was studied by gel electrophoresis. BLM A2 and BLM B2 produced a comparable extent of dsb. In various experiments, BLM A2 and BLM B2, at 22-41 ng/mL, degraded 50% of the form I DNA into 33-38% form II and 12-17% form III DNA. BLM B1' produced ssb and dsb at a ratio similar to that of BLM A2, but both at a rate less than half that of BLM A2. Phleomycin (PLM) D1 induced an equivalent amount of ssb but only one-eighth of dsb induced by BLM B2. The relatively lower extent dsb production for PLM D1 was observed either in borate buffer (pH 9.5) or in Tris-HCl buffer (pH 7.5) and in the presence or absence of exogenous Fe(II). Deamido-BLM A2 produced ssb to an extent approximately half that of BLM A2 and dsb to less than one-eighth that of BLM A2. The following conclusions were drawn. (1) BLM analogues produced ssb and dsb to different extents and ratios. (2) The ratio of dsb to ssb varied depending on the analogue, indicating a lack of a direct correlation between ssb and dsb. (3) The extent of ssb and dsb was affected by modifications on both the C- and N-terminal half-molecules of BLM: modification of either the N-terminal amide or the bithiazole greatly reduced dsb, whereas changes in structure or charge in the C-terminal amine affected ssb and dsb to a similar extent.

Interactions of a new antitumor antibiotic BBM-928A with deoxyribonucleic acid. Bifunctional intercalative binding studied by fluorometry and viscometry

A new actinoleukin-like antitumor antibiotic, BBM-928A, has been shown to interact with isolated DNA molecules. BBM-928A contains two substituted quinolines linked by a cyclic decapeptide. Quenching effects of the covalently closed superhelical PM2 DNA on the BBM-928A fluorescence revealed a strong interaction with an apparent association constant of 1.93 x 10(7) M-1 and with 11 deoxyribonucleic acid (DNA) nucleotides per BBM-928A binding site. Viscometric studies indicated the BBM-928A induced an unwinding-rewinding process of the closed superhelical PM2 DNA typically observed for DNA intercalators. The unwinding angle (43 degrees) induced by BBM-928A was almost twice that of the ethidium bromide (26 degrees), a monofunctional intercalator. The BBM-928A-induced increase of the helix length of sonicated rodlike calf thymus DNA was approximately 1.5-fold that induced by the ethidium bromide. On the basis of these observations, we concluded that BBM-928A bifunctionally intercalated with DNA in a manner similar to the bifunctional intercalation of echinomycin.

Comparison of DNA damage and single- and double-strand breakage activities on PM-2 DNA by talisomycin and bleomycin analogs

Single- and double-strand breakage of isolated PM-2 DNA by structural analogs of the glycopeptide antitumor antibiotics bleomycin (BLM) and talisomycin (TLM) was investigated. Breakage of PM-2 DNA was determined by two systems: an ethidium bromide fluorescence assay; and agarose gel electrophoresis. The fluorescence assay, which measures total breakage of DNA including single- and double-strand breakage and alkaline labile damage, showed that the BLM's, A2 and B2 induced more total DNA breakage than did the TLM's A, B, S2b, and S10b. As measured by the comparison of the concentration of analog required to cause 50% breakage of superhelical DNA, BLM's A2 and B2 were 10 times more active than TLM's S2b and S10b and 25 times more active than TLM's A and B. Gel electrophoresis, which measures the extent of both single- and double-strand breakage of DNA, showed that at equivalent levels of breakage of superhelical DNA each of the TLM's caused more double-strand breakage of DNA than did the BLM's. Thus, the structural alterations near the bithiazole in the TLM's, which distinguish them structurally from the BLM's, result in a reduction of the total PM-2 DNA breakage activity and enhanced production of double-strand breaks relative to single-strand breaks by TLM when compared to BLM.

Effects of second-generation platinum analogs on isolated PM-2 DNA and their cytotoxicity in vitro and in vivo

Using PM-2 DNA and cytotoxicity assay systems, we have studied several second-generation platinum analogs and compared these to the parent compound cis-diamminedichloroplatinum(II). These results indicate that all planar platinum(II) congeners induced similar effects upon interaction with PM-2 DNA, i.e., alteration of the tertiary DNA conformations. The reactivity of the analogs with DNA depended on the activity of the leaving groups. Octahedral platinum(IV) compounds, however, induced breakage of covalently closed circular PM-2 DNA, and the effects were not inhibited by either chloride or ethylenediaminetetraacetate. This suggests that breakage of isolated PM-2 DNA may be related to the axial trans bonds rather than the equatorial cis bonds of the solvated platinum(IV) compounds, since the activity of the dichloroplatinum(II) compounds has been shown to be inhibited by chloride ions. Studies on the in vitro and in vivo cytotoxicity of the platinum analogs demonstrated that the reactivity of analogs against PM-2 DNA correlated with in vitro and in vivo potencies. The reactivity with PM-2 DNA appeared to depend on the characteristics of the leaving group.

Interaction of cis-diamminedichloroplatinum(II) with PM-2 DNA

The interaction of cis-diamminedichloroplatinum(II) (CDDP) with PM-2 DNA was studied using two techniques: (a) agarose gel electrophoresis of PM-2 DNA conformation isomers after CDDP binding; and (b) viscometric measurement of different forms of CDDP-bound PM-2 DNA. In both systems, the results indicated that the DNA isomers interacted differently with CDDP. CDDP induced a decrease of viscosity upon interacting with single-strand broken relaxed circular (Form II) and double-strand broken linear (Form III) PM-2 DNA's. These observations are consistent with a "DNA shortening effect" proposed by Cohen et al. [Science (Wash. D. C.), 203: 1014-1016, 1979] and Macquet et al. [Biochimie (Paris), 60: 901-914, 1978] When covalently closed circular (Form I) PM-2 DNA was used, increasing concentrations of CDDP induced an initial slight increase and then decrease of electrophoretic mobility to the degree that it comigrated with CDDP-bound Form II DNA. Further addition of CDDP restored the electrophoretic mobility of Form I DNA. Corresponding changes in the viscosity of CDDP-bound Form I DNA showed an initial decrease, then an increase, and a final prolonged decrease of viscosity. These effects are similar but not identical to those induced by either DNA intercalators (e.g., ethidium bromide) or certain DNA denaturating agents (e.g., formaldehyde, ultraviolet light, alkali trichloroacetate, methylmercuric hydroxide, and carbodiimide). Thus, CDP may induce a DNA superhelix-unwinding process followed either by rewinding or a denaturation process or both. Quantitative analysis of the agarose gel electrophoretic pattern plus sucrose density gradient centrifugation studies also indicated that there was little DNA strand breakage induced by CDDP treatment.

Changes in RNA polymerase II in a cell cycle-specific temperature-sensitive mutant of hamster cells

tsAF8 cells are a temperature-sensitive mutant of BHK cells that arrest at the nonpermissive temperature in the G1 phase of the cell cycle. The activity of solubilized RNA polymerase II and its ability to bine [3H]-gamma-amanitin decrease in tsAF8 cells at 40.6 degrees, with a half-life of approximately 10 hr. No appreciable changes occur in these two parameters in tsAF8 cells at 34 degrees or in BHK cells at either 34 degrees or 40.6 degrees. Protein synthesis is not appreciably affected for at least 24 hr after tsAF8 cells are shifted to 40.6 degrees. These results indicate that in tsAF8 cells at the nonpermissive temperature, there is a defect in either the synthesis, the assembly, or the stability of RNA polymerase II, and that the loss of RNA polymerase II molecules is not due to widespread cellular damage.

Transcription and circular dichroism of chromatin in lymphoblastoid cell lines during proliferation and quiescence

RNA polymerase activity of nuclei and positive circular dichroism ellipticity in the 250--300 nm region of chromatin were studied in three lymphoblastoid cell lines: HRI, an Epstein-Barr Virus (EBV) positive virus-producing line; Raji, and EBV positive virus-producing line; Raji, an EBV positive non-producer line; and SU-AMB-1, and EBV negative line. Raji consistently exhibited the highest and SU-AMB-1 the lowest polymerase activity and ellipticity. All lines showed higher RNA polymerase activity and positive ellipticity when exponentially growing than when stationary. In Raji it was shown that changes in RNA polymerase activity and chromatin ellipiticity were parallel. The changes in RNA polymerase activity of nuclei and circular dichroism ellipticity correlated with those of the proliferative state but not with the number of viral genomes or the production of virus or viral antigens.

Evidence for an essential arginine recognition site on adenosine 3':5'-cyclic monophosphate-dependent protein kinase of rabbit skeletal muscle

On the basis of the chemical and structural features of the amino acid sequences in the vicinities of phosphorylatable hydroxyamino acid residues in several of the well-known protein substrates for skeletal-muscle cyclic AMP-dependent protein kinase, it is hypothesized that the phosphorylatable residue at position i and arginine residue at position i-3 of these protein substrates are located on a peptide turn on the hydrophilic protein surface. It is further hypothesized that there is an arginine-recognition site near the active centre on the protein kinase. This site is essential for the function of cyclic AMP-dependent protein kinase, for, not only does it recognize specifically the exposed arginine residue of the protein substrate, but, more importantly, via the interaction with arginine-(i--3), it may help to steer the topologically adjacent serine-i into proper orientation on the nearby active centre for phosphorylation. Model-building and kinetic data that provide support for the proposed hypotheses are presented.

Analysis of the prodrug 7-acetylacroninium perchlorate in presence of the parent compound acronine

Analysis of acronine and the prodrug acetylacroninium perchlorate in parenteral solutions is described. The unstable prodrug reacts quantitatively with the nucleophilic agent aniline by an unusual mechanism to form a phenylimino derivative of acronine. This derivative and acronine itself were determined by a spectrophotometric two-component method.

A structural model for the cholesterol-phosphatidylcholine complexes in bilayer membranes

Based on the structural properties of phospholipid and cholesterol molecules, and making use of the known structural and motional effects of cholesterol and its analogs on phospholipid bilayers, a model for the cholesterol-phosphatidylcholine complex is proposed. In this model, the 3beta-hydroxyl group of cholesterol is assumed to engage in hydrogen bonding with the carbonyl oxygen of the fatty acyl groups in phospholipids. Some specific configurations of the saturated and unsaturated fatty acyl chains of the phospholipid are suggested to participate in van der Waals attractive interactions with the apha and beta surface of the steroid nucleus.

Isolation of transcriptionally active chromatin from mammalian nucleoli

Nucleoli isolated from HeLa cells are functionally active but contain large amounts of RNA and proteins (RNA/DNA ratio 1:1; protein/DNA ratio 7:1). We have isolated from the nucleolus a DNA-protein complex that has the characteristics of nucleolar chromatin (RNA/DNA ratio less than 0.05:1; protein/DNA ratio 1.7:1). This nucleolar chromatin has most of the transcriptional activity of the intact nucleolus and, as assayed by circular dichroism and dye binding, has largely preserved its structure. The isolation of a transcriptionally active, fragment of chromatin, which constitutes only a small part of the total genome and codes for only one recognizable product, offers several advantages for the study of chromatin structure and function.

The role of nuclei and nucleoli in the control of cell proliferation

A number of changes have been reported to occur in chromatin of quiescent cells stimulated to proliferate. These changes, indicative of increased transcriptional activity, occur in the early prereplicative phase, several hours before the onset of DNA replication, and are detectable not only in chromatin, but also in isolated nuclei and in whole cells. Most of the increased transcriptional activity can be attributed to an increased activity of the nucleolus; however, extranucleolar genes are also important in the regulation of the cell cycle flow, from G0 to S.

Circular dichroism studies of ethidium bromide binding to the isolated nucleolus

Circular dichroism in the 300-360 nm region and fluorescence induced by intercaltating binding of ethidum bromide to both DNA and RNA components were studied in isolated HeLa nucleoli. Both DNA and RNA compoents contribute to the induced dichroic elliticity. Digestion of nucleoli by RNase or DNase shows that most of the induced ellipticity comes from the DNA component. In nucleoli with an RNA/DNA = 0.8/1.0 the RNA component gives only 20% of the total ellipticity when measured at an ethidium bromide/DNA = 0.25. Spectro-fluorometric titration shows that ethidium bromide intercalates mostly into DNA in nucleoli. Both circular dichroism and fluorescence studies indicate that both DNA and RNA components in isolated nucleoli are less accessible to intercalating binding by ethidium bromide when compared to purified nucleolar DNA, DNA in chromatin or purified ribosomal RNA. Circular dichroic measurements of intercalating binding of ethidium bromide to to nucleoli may be used to study changes in nucleoli under different physiological or pathological conditions.

Circular dichroic studies of the DNA and RNA of nucleoli

Circular dichroism (CD) in the 240-300-nm region was used to study the conformation of DNA and RNA complexed with proteins in isolated nucleoli form HeLa cells. Deoxyribonuclease or ribonuclease digestion was employed to obtain (1) the individual CD spectra of nucleolar DNA or RNA in complex form with proteins, or in free form; and (2) the experimental CD baseline correction to exclude contributions from nonnucleic acid sources such as light scattering artifacts and proteins. The CD spectrum of nucleolar DNA in DNA-protein complexes was highly reduced in ellipticity in comparison with protein-free DNA. It showed a positive peak at 283 nm with a molar ellipticity [theta]283 = 1200 deg cm2 dmol-1 and a crossover at 262 nm. Addition of sodium dodecylsulfate shifted the peak to 276 nm with [theta]276 8000 deg cm2 dmol-1 and a crossover at 254 nm. The CD spectrum of nucleolar RNA in RNA-protein complexes was also reduced in comparison with protein-free RNA, showing a peak at 269 nm ([theta]269 = 6900 deg cm2 dmol-1), and a crossover at 250 nm. Addition of sodium dodecyl sulfate shifted the peak to 265 nm with [theta]265 = 18 000 deg cm2 dmol-1 and a crossover at 246 nm. The low ellipticity of both nucleolar DNA and RNA when complexed with proteins was increased by treatment with sodium chloride, urea, or heparin. This suggests that some ionic, hydrophobic, and hydrogen bondings are involved in the nucleic acid-protein interaction in nucleolar chromatin similar to that observed in nuclear chromatin.

Structure in the polar head region of phospholipid bilayers: A 31P [1H] nuclear Overhauser effect study

The structure of the head-group region of some phospholipid bilayers in vesicle form has been studied and an intermolecular association of the N-methyl protons of phosphatidylcholine (PC) with the phosphate of phosphatidylethanolamine (PE) in mixed vesicles has been identified. Observation of a 31P[1H] nuclear Overhauser effect (NOE) in the phosphorus nuclear magnetic resonances of both PC and PE in mixed vesicles demonstrates an intimate dipolar interaction between some protons and the phosphorus nuclei. Substitution of deuterium for the N-methyl protons of PC eliminated the majority of the effect and necessitated the construction of a model of the bilayer surface in which the N-methyl protons of PC could interact closely with the phosphates of neighboring PE molecules. The predominant orientation of the head group must then be parallel to the bilayer surface. The amino protons of PE do not contribute significantly to the observed NOE. A corollary of these results is that there is little if any tendency for either PC or PE in the mixed vesicles to segregate into separate domains. A decrease in NOE in sphingomyelin vesicles on going from H2O to D2O suggests that an exchangeable proton contributes to the NOE. In addition the low value of the NOE observed in D2O suggests that the head-group conformation of sphingomyelin differs from that of PC.

Preferential inhibition of herpes-group viruses by phosphonoacetic acid: effect on virus DNA synthesis and virus-induced DNA polymerase activity

In tissue culture phosphonoacetic acid (PAA) specifically inhibited DNA synthesis of human cytomegalovirus (CMV), murine CMV, simian CMV, Epstein-Barr virus, and Herpesvirus saimiri. Fifty to one hundred micrograms per milliliter PAA completely inhibited viral DNA synthesis with no significant damage to host cell DNA synthesis. In vitro DNA polymerization assays showed that 10 μg/ml of PAA specifically inhibited partially purified human CMV-induced DNA polymerase, while little inhibition of host-cell DNA polymerase activity was found. The specific inhibition of herpes-group virus DNA synthesis with little toxicity to host cells suggests that PAA has great potential as an antiherpesvirus therapeutic agent.

Headgroup conformation and lipid--cholesterol association in phosphatidylcholine vesicles: a 31P(1H) nuclear Overhauser effect study

The nuclear Overhauser effect has been observed in the nuclear magnetic resonance spectra of 31P. The information content of the nuclear Overhauser effect has been applied to the structure and dynamic properties of phosphatidylcholine vesicles. In the vesicles only 1/3 of the theoretical maximum nuclear Overhauser effect enhancement is observed. This result is accounted for by dipolar interactions between the N-methyl protons and the phosphate of phosphatidylcholine, and a correlation time for internal motion of 1.4 X 10(-9) sec. Addition of up to 30% cholesterol does not change the nuclear Overhauser effect enhancement or spin-lattice relaxation time of the vesicles. It is argued that the OH group of cholesterol is hydrogen bonded to the ester carbonyl oxygen of the phosphatidylcholine molecules.

Further characterization of gradient-fractionated submitochondrial membrane fragments from beef heart mitochondria

We have recently reported that with a linear sucrose density gradient centrifugation two distinct types of membrane fragments, designated as X- and Y-fragments are obtained (Huang, C. H., Keyhani, E. and Lee, C. P. (1973) Biochim. Biophys. Acta 305, 455-473). Further characterization of these two membranes fragments is reported. (1) Potassium chloride at the concentration of 0.15 m extracts 7% and 30% of cytochrome c from the X- and Y-fragments, respectively. (2) When cytochrome c was added to the mitochondrial suspension prior to sonication, the cytochrome c content was increased by 6-8-fold in both X- and Y-fragments. Subsequently KC1 extraction resulted in loss of cytochrome c by 1/4 in the X- and by 2/3 in the Y-fragments. (3) With partially inhibitory concentrations of KCN, cytochrome c in either the X- or the KC1 extracted X-fragments showed uncoupler-sensitive, biphasic reduction kinetics upon the addition of NADH to the oligomycin-supplemented system. Under identical conditions rapid first order reduction kinetics were seen for cytochrome c in Y-fragments supplemented with either oligomycin or oligomycin + carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). (4) When cytochrome c was added to the mitochondrial suspension after sonication, a significant amount of cytochrome c was bound to both X- and Y-fragments, but was readily removed with a high ionic strength medium. (5) Lubrol had little effect on the ATPase activity of the X- and the Y-fragments, suggesting a lack of membrane-buried ATPase. (6) Partial depletion of ATPase in X-fragments did not induce an increase in reactivity towards externally added cytochrome c. (7) Both the X- and the Y-fragments showed an energy-linked fluorescence enhancement of 8-anilinonaphthalene-1-sulfonate and an energy-linked fluorescence decrease of quinacrine. (8) In the presence of K-+ nigericin alone or in combination with valinomycin exhibited a stimulating effect on the rate of NADH oxidase of the oligomycinsupplemented X- and Y-fragments.

Differential interaction of cholesterol with phosphatidylcholine on the inner and outer surfaces of lipid bilayer vesicles

The separate identification of the -N(+)-(CH(3))(3) groups located on the outside and inside of phospholipid bilayers observed in proton magnetic resonance spectroscopy upon addition of low concentrations of praseodymium ion was exploited to investigate the effects of incorporated cholesterol. Only about 7% of the phosphate groups on the outside of the bilayer belong to a class of strong binding or shifting sites. Upon addition of up to about 30% cholesterol to egg lecithin bilayers, no changes in chemical shift or ratio of areas of peaks due to outer and inner -N(+)(CH(3))(3) groups appear. At about 30% incorporated cholesterol, an abrupt decrease occurs in the chemical-shift difference between -N(+)(CH(3))(3) groups located on the outer and inner bilayer surfaces, and an abrupt increase occurs in the ratio of the areas of the two peaks. For L-alpha-dipalmitoyl lecithin bilayers, an abrupt change in chemical-shift difference occurring between 10 and 20% cholesterol is not accompanied by a change in the relative number of -N(+)(CH(3))(3) groups located on the outer and inner surfaces. These results are interpreted as due to the homogeneous distribution of up to 30% cholesterol in egg lecithin bilayers. Above 30%, cholesterol is asymmetrically distributed in favor of the inner layer. In egg lecithin with a variety of polyunsaturated side chains, the side chains with the greater number of double bonds are preferentially displaced by high concentrations of cholesterol, which accounts for the increase in the ratio of outer to inner -N(+)(CH(3))(3) groups. Such preferential displacement by cholesterol cannot occur with the saturated L-alpha-dipalmitoyl lecithin. It is suggested that modified phospholipid vesicles of low radii of curvature may provide high concentrations of "active sites" present in membranes.

DNA of Epstein-Barr virus detected in tissue of Burkitt's lymphoma and nasopharyngeal carcinoma

The association of Epstein-Barr virus (EBV) DNA with African tumors was examined by the method of hybridization with complementary RNA. 22 out of 23 biopsies of Burkitt's lymphoma and 18 out of 23 biopsies of nasopharyngeal carcinoma were found to contain EBV DNA. The number of EBV genome equivalents per cell ranged from four to 113. Five out of 24 other African tumors, two adenocarcinomas, and one each of melanoma, reticulum cell sarcoma, and carcinoma of the antrum, also contained EBV DNA.