The effect of splenectomy, produced chemically by means of ethylpalmitate, on the formation of heteroagglutinins in the rat]

The formation of heteroagglutinins against human O-erythrocytes was pursued in Wistar rats splenectomized "chemically" by means of intravenous injections of ethyl palmitite. Contrary to some data in literature the initial inhibition in the formation of antibodies was replaced by a significant titre increase ranging from the 8th to the 14th day following immunization. The tween 20 contained in the emulsion of ethyl palmitic did not influence the formation of heteroagglutinins. The examinations show that a possible use of palmitic ethyl for immunosuppression is questionable.     

A bead and spring model for the stiffness of DNA.

The chain stiffness of linear native DNA is represented by a generalized bead and spring model recently proposed. It incorporates molecular rigidity by means of springs between beads, which are second neighbors along the contour of the chain. These springs are equivalent to elastic forces having longitudinal and transversal contributions. The model is compared with existing experimental data of sedimentation and low-angle light scattering to obtain the statistical parameters of DNA. The value of the statistical length obtained with this model is 1300 Å. The same value is obtained with the wormlike chain. Throughout this analysis, excluded volume is left out as a simplifying assumption.     

Recovery from ethyl methanesulphonate-induced genetical damage in barley. Independence of sodium azide treatment

Barley seeds were treated for 3 h at 25°C with 240 mM ethyl methanesulphonate (EMS), washed for 18 h, treated with various concentrations of unbuffered sodium azide (pH 6.7–7.3) for 3 h at 25°C, re-dried to 30% water content and either sown immediately or stored at 25°C for 12 days and then sown. The synergistic action of sodium azide post-treatment has been demonstrated only for the EMS-induced M₁ germination reduction, while the EMS-induced M₁ sterility and the yield of M₂ chlorophyll mutants were unaffected. The ?storage” recovery from EMS-induced mutagenic effects was insensitive to sodium azide post-treatment. The 12 day-seed storage at 25°C brought about an improvement of M₁ germination, M₁ survival, M₁ fertility and a decrease in the amount of M₂ mutants, regardless of whether sodium azide post-treatment was applied or not.     

Association of ribosomal subunits. IV. Polyamines as active components of the association factor from Bacillus stearothermophilus.

The association of ribosomal subparticles induced by several associating agents has been studied under different conditions. The following observations were made: 1. Spermidine was able to produce the association of subunits, and the concentration and temperature curves of this reaction were similar to those obtained with association factor. The product formed in the latter case was more stable. 2. The association at low Mg2+ concentration was higher with association factor than with polyamines. 3. The temperature-dependent binding of spermidine to 30-S subunits formed an active complex, which was converted into the 30S-50S couples by the addition of 50-S subparticles at low temperature. A similar behaviour has been previously shown for the complete association factor and its low molecular weight fraction. 4. The same unstable form of 30S-50S couples has been obtained either with spermidine or with the low molecular weight component (AFII) of the association factor. In both cases the protein fraction AFI was able to complete the reaction by stabilizing the subunit couple. 5. After glutaraldehyde fixation the products of the reactions with spermidine or association factor behaved in a similar way when they were submitted to long sucrose-gradient centrifugations. 6. The analysis of association factor preparations has shown that they contain spermidine as well as spermine. The polyamine levels in association factor could account for part of the total associating activity.     

Penicillinamidohydrolase inEscherichia coli

Substrate specificity of the bacterial penicillinamidohydrolase (penicillinacylase, EC 3.5.1.11) fromEscherichia coli was determined by measuring initial rates of enzyme hydrolysis of different substrates within zero order kinetics. SomeN-phenylacetyl derivatives of amino acids and amides of phenylacetic acid and phenoxyacetic acid of different substituted amides of these acids or amides, structurally and chemically similar to these compounds, served as substrates. Significant differences in ratios of initial Tates of the enzyme hydrolysis of different substrates were found when using a toluenized suspension of bacterial cells or a crude enzyme preparation, in spite of the fact that the enzyme is localized between the cell wall and cytoplasmic membrane, in the so-called periplasmic space.N-phenylacetyl derivatives are the most rapidly hydrolyzed substrates. Beta-phenylpropionamide and 4-phenylbutyramide were not utilized as substrates. The substrate specificity of the enzyme is discussed with respect to a possible use of certain colourless compounds as substrates, hydrolysis of which yields chromophor products suitable for a simple and rapid assay of the enzyme activity.     

Possibilities of the conjugation process in mycobacteria

Results obtained when studying conjugation in mycobacteria by means of different methods are summarized. The method of conjugation on surface of a solid complete medium was tested with different auxotrophic mutants of different strains ofMycobacterium smegmatis. It was not possible to obtain positive results even by means of the above method. This was probably due to unsuitability of the chosen strains ofMycobacterium smegmatis. Preparation of the donor strain by transfer of the F factor fromEscherichia coli F’ORF 1ade ⁺ lac⁺ pro⁺ toMycobacterium phlei PA adeStm ^r by means of sexduction is described. Frequency of the phenotype PAade ⁺ Stm^r increased in the average by two and a half orders of magnitude with respect to the control, however, a further transfer from cultures of the cellsade ⁺ Stm^r to cells ade could not be demonstrated. Experiments aimed at transferring the R factor from strainsEscherichia coli K-12 toMycobacterium phlei were unsuccessful.     

The role of immune pig colostrum,serum and immunoglobulins IgG,IgM, and IgA in local intestinal immunity against enterotoxic strain ofEscherichia coli 055 in germfree piglets

The protective effect of pig immune colostrum, serum and immunoglobulins IgG, IgM and IgA against the enterotoxic strain ofEscherichia coli O55, was studied in newborn germfree piglets. This strain produced accumulation of fluid and dilatation of intestine when injected into the ligated ileal segment of germfree piglets, which is considered to be the typical effect of enterotoxins. Erosion of the intestinal epithelium and penetration of bacteria into the submucosa were also observed. Immune serum, colostrum and all the immunoglobulin classes used produced a local protective effect, IgA being most effective. The mechanism of protection conferred by these immunoglobulins is discussed with respect to the possible pathogenic action of enterotoxicEscherichia coli O55 in the intestinal tract of immunologically virgin germfree piglets.     

Effect of some antiestrogens and aromatase inhibitors on androgen induced sexual behavior in castrated male rats

The effect of antiestrogens (MER-25, ICI-46474, and cis-clomiphene) and aromatase inhibitors (5-α-androstanedione, metopirone, and aminoglutethimide) on androgen induced copulatory behavior was tested in sexually inexperienced castrated male tats. Daily injections of 1 mg testosterone (T) for 21 days induced sexual activity in most subjects (61% mounting). Daily pretreatment with MER-25 or cis-clomiphene at three dose levels did not block the behavioral response to T. ICI-46474 at the high dose level (1 mg/kg) elicited a significant depressory effect on the sexual behavior of the T treated castrated rats. A single injection of 6 mg testosterone propionate (TP) induced mounting behavior in 56% of the tested rats within 120 hr. Treatment with metopirone or 5 α-androstanedione (injections every 12 hr for 96 hr) did not inhibit the response to TP. By contrast, aminoglutethimide (5 or 15 mg every 12 hr for 96 hr) abolished the behavioral response to androgen.     

Interaction of ethidium bromide with the transport system for monovalent cations in yeast

Summary Ethidium was found to be taken up by yeast cells in a process that, at certain concentrations has the main following characteristics: a) a substrate is required; b) it presents cooperative kinetics, withn, according to the Hill equation 3; c) ethidium can be concentrated more than 100-fold; d) the uptake is inhibited by Ca²⁺; e) the uptake of the dye is inhibited by monovalent cations with a selectivity pattern similar to that observed in their transport by yeast; f) ethidium inhibits the uptake of K⁺, and, at concentrations up to about 250 m produces a competitive inhibition on the uptake of Rb⁺; and g) ethidium produces the same effects as K⁺ on respiration and the extrusion of H⁺. It is concluded that ethidium is taken up by yeast cells in a selective way by the same transport system normally employed for monovalent cation uptake.