Cyclic variations in cell-mediated immunity to skin allografts detected by the technetium-99m microcytotoxicity assay

The technetium-99m microcytotoxicity assay has been used to detect cell-mediated immunity in CS7BL/6 mice sensitized with A/J skin allografts. Our initial studies of the quantitative in vitro assessment of lymphocyte-mediated cytotoxicity in mice rejecting first-set skin allografts revealed a simple monophasic response peaking at 14 days postgrafting and declining to control levels by 21 days. Subsequent experiments in which the development and persistence of immunity was assessed at daily intervals from 9–21 days postgrafting revealed that the response was considerably more complex. A cyclic rise and fall in killer activity was evident. The first peak occurred 10–13 days after grafting and the second one 3–5 days later. A third peak of cytotoxic activity sometimes could be detected 16–19 days postgrafting. An attempt was made to characterize the phenomenon by studying the cytocidal effects resulting from the admixture of high- and low-responding lymphocyte populations. An intermediate effect generally was observed when lymphocytes with maximal killer activity were combined in equal numbers with those having decreased reactivity. Varying the ratio of high-and low-responding cells resulted in changes in the net killing effect which was consistent with dilution of more reactive lymphocytes with less reactive ones. Mixing lymphocytes from two peak periods produced a maximum killing effect at all effector to target cell multiplicities. Failure to demonstrate modulation of the reactivity of high-responding cells by low-responding ones suggests that these cyclic variations were not mediated by suppressor cells although a role for humoral factors cannot be excluded at the present time. Alternatively, the cyclic pattern may have been due to the specific depletion and subsequent regeneration of cytotoxic lymphocytes in the lymph nodes of sensitized animals.     

Electrophoretic investigation of phenol oxidases in stratified apple seeds

The substrate specificity of apple seeds phenol oxidases was investigated in polyacrylamide gel electropherograms. The nonspecifico-diphenol oxidases were distinguished as well as fractions showing the specificity for some structural elements of substrate molecule. The role of particular oxidases in phloridzin transformations in apple seed was discussed.     

The influence of cytokinins on apple embryo photosensitivity and acid phosphatase activity during stratification

Kinetin (KIN) and benzyladenine (BA) stimulate to different extent the germination of apple embryos isolated from dormant seeds or seeds submitted to stratification. KIN is much more active in the replacement of light requirement in apple embryos germination. Both cytokinins decrease the photosensitivity of embryos isolated from the seeds stratified less than one month, but only BA accelerates the appearance of the second photosensitivity maximum, normally occuring on the 70th day of stratification. Both cytokinins stimulate the activity of acid phosphatase between the 30th and 50th day of apple seed stratification. The stimulation between the 50th day and the end of stratification is exerted only by KIN. These differences allow to discuss the specificity of action of particular cytokinins during the after-ripening and germination of apple embryos.     

Chemical composition of gas vesicles isolated from Anabaena flos-aquae

Summary Chemical analysis of purified preparations of gas vesicles isolated from the filamentous blue-green alga Anabaena flos-aquae has shown that they are similar in composition to those isolated from the unicellular alga Microcystis aeruginosa by Jones and Jost (1970), being proteinaceous structures, free of lipid and carbohydrate. The gas vesicle protein from Anabaena contains the same 14 amino acids, in broadly the same proportions; in addition there is a small proportion of proline. No sulphur-containing amino acids are present. The empirical formula, suggested by the amino acid ratios, indicates a molecule of 15000 MW.     

Effect of Elevated Temperatures on Protein Synthesis in Escherichia coli

Upon a temperature shift from 30 C to 42 to 44 C, Escherichia coli experiences a transient slowdown in rate of optical density increase, uridine incorporation, and amino acid incorporation. The data show that the primary target for thermal inactivation is a molecule(s) required for the initiation of protein synthesis. The effect on ribonucleic acid synthesis is a secondary effect.     

CYTOKINETICS OF THE S-180 ASCITES TUMOR SYSTEM

The cytokinetics of the S-180 mouse ascites tumor system was determined on Days 2, 4, 6 and 9 of growth. Studies included volume tumor growth, per cent labeled mitoses curves, and repeated injections of tritiated thymidine. It was possible to extrapolate the cytokinetic compartment values to Day 0 of growth. Results indicate that the growth fraction of the S-180 system remains close to 1 throughout its growth, with progressive lengthening of G₁, S and G₂ times. Cell loss is minimal through 6 days but becomes significant thereafter. A theoretical growth curve constructed from cytokinetic values is similar to the actual volume growth curve.     

The salt-extractable fraction of dynein from sea urchin sperm flagella: An analysis by gel electrophoresis and by adenosine triphosphatase activity

Previous work has shown that the dynein from axonemes of sea urchin sperm consists of two distinct fractions which differ substantially in their extractability by salt. Upon gel electrophoresis of whole demembranated axonemes solubilized with sodium dodecyl sulfate, the dynein fraction shows two closely spaced bands with apparent molecular weights of 520,000 and 460,000; the proteins in these bands are termed the A and B components of the dynein. Similar electrophoresis of the soluble fraction obtained by extracting the axonemes with 0.5 M NaCl shows a single prominent band containing approximately half of the A component of the dynein (A₁ component). The residue of extracted axonemes contain the other half of the A component of the dynein (A₂ component) and all the B component. Densitometry of the bands indicates that the A₁, A₂ and B components of the dynein are present in approximately equal molar quantity. Electron microscopic studies show that the A₁ component of the dynein constitutes the outer arms on the doublet tubules. Assay of ATPase activity in 0.05 M KCl and l mM ATP indicates about 65% of the total ATPase activity becomes soluble when the A₁ component of the dynein is extracted with salt.