Sub-lethal autolysis : Modification of cell periphery by lysosomal enzymes

Lysosomal activation was induced in dog kidney and HEp-2 cells by treatment with anticellular serum and high concentrations (20 μg/ml) of vitamin A alcohol. The morphological changes accompanying the release of enzymes from activated lysosomes were described. Measurements of cell coat thickness by ellipsometry revealed that lysosomal enzymes released extracellularly were able to digest the coat. The scale of enzyme release was an important factor in determining the amount of coat digested. Complement-sufficient anticellular sera and high concentrations of vitamin A induced marked lysosomal activation and extensive digestion of the coat. Complement-deficient anticellular serum produced significantly less lysosomal labilization and only limited digestion of the coat. The digestion of the cell coat induced by these agents was prevented by pretreatment of the cells with either hydrocortisone or chloroquine.     

Stereochemistry of actinomycin binding to DNA : II. Detailed molecular model of actinomycin-DNA complex and its implications

The three-dimensional structure of a crystalline complex containing actinomycin D and deoxyguanosine (described in the previous paper) has shed light on the stereochemistry of actinomycin binding to DNA. The phenoxazone ring system on actinomycin intercalates between the base-paired dinucleotide sequence, GpC, while the peptide subunits lie in the narrow groove of the DNA helix and interact with deoxyguanosine residues on opposite chains through specific hydrogen bonds. The binding of actinomycin to DNA demonstrates a general principle which several classes of proteins may utilize in recognizing symmetrically arranged nucleotide sequences on the DNA helix.     

Intracellular pH electrode : Experiments on the giant squid axon

A new, easy method to produce and calibrate a 1-μm tip intracellular pH electrode is described. This antimony electrode and a micro-calomel electrode were inserted into the giant axon of Loligo pealii. The potential obtained when the axon was bathed in seawater corresponded to a pH of 7.0 ± 0.2. It was found that acidification of the external perfusate induced a drop in axoplasmatic pH leading to changes in the membrane electrical properties. Changes of resting or action potentials did not influence intracellular pH.     

Heterocycles from saccharide hydrazones : Part I. Saccharide 1,3,4-oxadiazoles

Oxidation, with iodine-mercuric oxide, of acetylated saccharide aroylhydrazones and of aromatic aldehyde hydrazones yields 5-aryl-2-(polyacetoxyalkyl)-1,3,4-oxadiazoles and 2,5-diaryl-1,3,4-oxadiazoles, respectively. On de-O-acetylation, saccharide oxadiazole acetates rearrange to the tautomeric, cyclic iminolactones which, on reacetylation, regenerate the starting oxadiazoles. Attempted dehydration of saccharide acetyl- and benzoyl-hydrazones by treatment with boiling acetic anhydride under reflux resulted in the formation of peracetylated N,N-diacetylhydrazones and-N-acetyl-N-benzoylhydrazones, respectively.     

Light scattering by cellulose : IV. Fibers with helical morphology

Solid-state light scattering has been used to study the scattering by the helically wound microfibrils in wood fibers. Scattering envelopes have been recorded from a section of Eastern spruce wood as well as a single fiber of Black spruce. Theoretical expressions for the intensity of light scattered by a continuous helix have been derived and found to be in fair agreement with the experimental results. A method of estimating the “pitch” and “tilt” of the helical segments is outlined.     

Fluorinated carbohydrates : Part XIII. 2-deoxy-2-fluoro-D-galactose

Reaction of trifluoro(fluoroxy)methane at ca. −80° with 3,4,6-tri-O-acetyl-D-galactal affords trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranoside (2, 39%), 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranosyl fluoride (3, 37%), trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-talopyranoside (4, 3%), and 3,4,6-tri-O-acetyl-2-deoxy-2-fluor-α-D-talopyranosyl fluoride (5, 2%). The structures of compounds 2–5 have been established by n.m.r. spectroscopy. Acid hydrolysis of 2 or 3 allords 2-deoxy-2-fluoro-D-galactose.     

Analysis of 5-methylcytosine in DNA: II. Gas chromatography

A method for analyzing 5-methylcytosine in DNA by gas chromatography is described. The method is based on degradation of the DNA to its free bases by treatment with trifluoroacetic acid and gas chromatography of the trimethylsilyl derivatives of the free bases. Chromatography of microgram amounts of derivatized material is conducted at isothermal conditions using a 3% SE-30 or 2% OV-225 column. The peak areas corresponding to cytosine and 5-methylcytosine are used to calculate the 5-methylcytosine/cytosine molar ratio in DNA. The lower limit for detection of 5-methylcytosine in DNA by this method is a 5-methylcytosine/cytosine molar ratio of 0.001.     

Assembly of bacteriophage T4 tail fibers : III. Genetic control of the major tail fiber polypeptides

Purified preparations of complete T4 bacteriophage, tail fiberless particles, whole tail fibers and four tail fiber precursors were dissociated by heating briefly at 100 °C in 1% sodium dodecyl sulfate containing 1% mercaptoethanol. Analysis of the dissociated structures by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and mercaptoethanol revealed two high molecular weight (150,000 and 123,000 daltons) polypeptides as major tail fiber components. These two components could be easily identified by autoradiography of sodium dodecyl sulfate gels of radioactively labeled infected cell extracts. The larger of the two was missing from extracts of cells infected with gene 34 amber mutants, and the smaller from extracts of cells infected with gene 37 amber mutants. It is concluded that the two components represent the products of genes 34 and 37 (P34 and P37), respectively. Molecular weight calculations indicate that two copies of each polypeptide are present in each complete tail fiber. Amber mutations in genes 38 and 57 were found to affect the apparent solubility of P34 and P37 and their resistance to dissociation in cold sodium dodecyl sulfate, but not their synthesis. Based on these results, the previously reported pathway of tail fiber assembly (King & Wood, 1969) has been reformulated in more detail.     

Immobilization antigens of Tetrahymena pyriformis : I. Assay and extraction

A method using immunodiffusion has been established to assay the two mutually exclusive temperature dependent immobilization antigens, H and T, of Tetrahymena pyriformis. Specific antiserum was obtained by exploitation of allelic or temperature induced variations among inbred strains for absorption of antisera prepared against whole cells. The antigens were extracted both from isolated cilia and from whole cell bodies. Mild detergent extraction was found to be more efficient than mechanical disruption of the cells by freeze-thawing. The sedimentation behavior in sucrose density gradients of active H antigen was the same, whether freeze-thaw or detergent extracted; similarly, the sedimentation behavior of T was the same following the two extraction methods. Extraction with acetic acid, as reported by others, solubilized the same material as the detergent, but the acid denatured the antigen. An estimate of the molecular weight of the antigen of 29 000 for H and 23 000 for T was made.     

Filamentous bacterial viruses : I. DNA synthesis during the early stages of infection with fd

During the first ten minutes after infection of bacteria with fd, the rate of DNA synthesis in an infected culture becomes several-fold larger than the rate in a parallel uninfected culture. This stimulation of rate is due to the synthesis of 100 to 200 double-stranded forms of viral DNA, superimposed on continuing bacterial DNA synthesis. At the end of the ten-minute period, the rate of viral plus bacterial DNA synthesis stops increasing, and remains constant for the next 50 minutes. The abrupt decrease in acceleration of net DNA synthesis corresponds in time to the onset of synthesis of single-stranded viral DNA.     

Structure of yeast hexokinase-B: I. Preliminary X-ray studies and subunit structure

Initial X-ray diffraction studies of large single crystals of yeast hexokinase-B provide information on its subunit structure and show the crystals to be suitable for a high resolution structure determination. Patterson maps of the native protein crystals suggest that the two 50,000 molecular weight subunits are identical, or very nearly so, and that they are related by an approximate rather than a true diad axis; that is, one subunit is translated relative to the other by 3.6 Å along the molecular symmetry axis. This results in heterologous subunit interactions rather than the isologous interactions expected.     

Quinacrine fluorescence of metaphase chromosomes : Identical patterns in different tissues

The quinacrine mustard fluorescence patterns of the metaphase chromosomes of different tissues of the same plant species were found to be identical. Similar studies of the chromosome regions on human material gave the same result.