Macromolecular insoluble cold globulin (MICG): a novel protein from mouse lymphocytes. III. Relationship to the mixed lymphocyte reaction and effect of anti-MICG antiserum in vivo.

In the present communication we have examined the relationship between the synthesis of macromolecular insoluble cold globulin (MICG) and the mixed lymphocyte reaction (MLR). In addition, we have studied in vivo the effect of antiserum to MICG on the antibody response to sheep red blood cells. The experiments indicate that MICG synthesis compared to either IgM or total protein is selectively stimulated in responder T cells exposed to allogeneic stimulator cells in the MLR. Furthermore, cytotoxicity studies utilizing anti-MICG antiserum demonstrated that T cells bearing MICG on their surface are an essential component of the responder cell population in the MLR. In vivo administration of antiserum to MICG significantly suppressed both the primary and secondary antibody response to sheep red blood cells. A possible mechanism for this suppression is discussed.     

Molecular biology of liver regeneration

Liver regeneration is a good system for studying cell proliferation in an in vivo, physiologically controlled situation. Various hepatotrophic factors, neuromediators, hormones and growth factors, presumably acting in synergy, seem necessary to induce the switch from quiescence to proliferation. As a consequence of this activation, a number of changes occurs in the hepatocyte: modifications of the plasma membrane proteins; metabolic changes such as variations in albumin and fibrinogen concentrations, and induction of the acute phase proteins; induction of several specific mRNAs; variations in cAMP concentrations, and consequently in the activity of protein kinases and several other enzymes; modifications in chromosomal proteins; induction of proteins involved in DNA replication. A model has been constructed which is more a basis for reflexion than a theoretical model. It takes into account the possible connections between the different molecular events cited above. It is hypothesized that DNA replication is at least partly uncoupled from mitosis, and that the initial events of the proliferative response may be triggered by nutritional elements.     

Effect of histone H1, poly(ethyleneglycol) and DNA concentration on intermolecular and intramolecular ligation by T4 DNA ligase

The efficiency of ligation of linear DNA and the relative amounts of intramolecular versus intermolecular ligation may be triggered by a number of additive agents. The results show that it is possible to mimic the effect of poly(ethyleneglycol) 6000 by simply increasing DNA concentration about 15-fold: both the rate and the extent of the reaction are greatly enhanced, and intermolecular ligation is largely favored. However, in this case the stimulation by salts, which occurs in poly(ethyleneglycol) solutions, is not observed; we suggest that salts enhance the hydrophobic interactions between ligase and DNA that take place in the presence of poly(ethyleneglycol). We also show that histone H1, which is involved in the formation of chromatin fibers, is able to stimulate intermolecular ligation by T4 ligase. This effect is more specific than a simple neutralisation of the phosphate groups of the DNA by positive charges of the histone; it still occurs at 125 mM NaCl and in the presence of the four core histones. The implications of the finding concerning the mode of action of histone H1 on DNA are discussed.     

OXIDATION AND PHOSPHORYLATION PROCESSES IN BRAIN MITOCHONDRIA OF RATS EXPOSED TO CARBON DISULPHIDE

Abstract— The effects of acute and long-term exposure to CS₂ on oxidation and phosphorylation processes in brain mitochondria of rats were studied. Although rats developed different symptoms of poisoning, depending on the type of exposure, the brain mitochondria of both groups of animals exhibited the same types of disturbances in oxidative phosphorylation. The main characteristic of these disturbances was the uncoupling of oxidative phosphorylation indicated by lower respiratory control indices due to stimulation of oxidation of respiratory substrates by mitochondria in the metabolic state 4. This effect was accompanied by a decreased P:O ratio and a lower ATP-Pi exchange rate. An inhibitory effect of CS₂ on the energy transfer processes is also suggested.
The observed changes in oxidative phosphorylation were more distinct in the case of acute poisoning, with a longer period of an uninterrupted exposure enabling a more complete tissue saturation with CS₂, than in the case of long-term exposure with shorter periods of intoxication within the day.     

Stimulating effect of physical effort on the excretion of 5-hydroxyindoleacetic acid.

The excretion of 5-hydroxyindoleacetic acid, after work load, was studied. The physical effort evoked an increase in the excretion of 5-hydroxyindoleacetic acid. Under the control conditions no changes in the excretion of the investigated metabolite were found.     

Wood ants prefer conifers to broadleaved trees in mixed temperate forests

1. Wood ants, species of the subgenus Formica s. str., are one of the most important groups of insects in forest ecosystems due to their high abundance and activity.
2. We assessed the foraging pressure of Formica polyctena and Formica rufa, two dominant wood ant species in the Białowieża Forest. In addition, we compared coniferous and mixed stands in these respects.
3. In mixed stands F. polyctena visited more trees per plot than F. rufa. F. polyctena might forage a larger area due to higher population sizes, which further confirms higher foraging pressure of F. polyctena in comparison with F. rufa.
4. In our study area, host trees of the ant–aphid mutualism were larger in diameter than nonhost trees. The ants also preferred trees situated closer to their nests. In both mixed and coniferous stands, the most visited tree species was Norway spruce. Thus, we can conclude that Norway spruce seems to be preferred by the ant. The decline of living spruce in the Białowieża Forest may endanger their food source and impact the vitality of ant colonies.

     

Comparison of biochemical properties of DNA-topoisomerase I from normal and regenerating liver.

Biochemical properties of topoisomerase I from normal and regenerating rat liver were analysed using crude or fractionated nuclear extracts. We could not detect significative change in topoisomerase I content or activity (magnesium stimulation and inhibition by ATP) during the course of liver regeneration. Topoisomerase I can be resolved into two species of 97 kDa and 100 kDa, with the same pI of 8.2-8.6 as shown by two dimensional gel electrophoresis. The two polypeptides contained a non-phosphorylated precursor and others forms with variable degrees of phosphorylation. In-vitro dephosphorylation with alkaline phosphatase leads to the disappearance of the phosphorylated forms and inactivation of the enzyme. The affinity of topoisomerase I for chromatin (measured by salt elution) differs markedly between normal and regenerating liver: nearly 50% of topoisomerase I remained bound to the chromatin from normal liver at 250 mM NaCl whereas it was completely eluted from 24-h-regenerating-liver nuclei. The biological significance of these results is discussed.     

Effect of l-carnitine on liver cell membranes in ethanol-intoxicated rats

Ethanol intoxication is characterized by changes in cell metabolism which alter the structure and function of cell membrane components, including phospholipids and integral membrane proteins. The interaction of food nutrients with ethanol may modulate alcohol toxicity. One such compound is l-carnitine (l-3-hydroxy-4-N,N,N-trimethylaminobutyrate), which is also an antioxidant. Here we investigate l-carnitine as an antioxidant and assess its effect on the composition and electrical charge of liver cell membranes in ethanol-intoxicated rats. Qualitative and quantitative phospholipid composition and the presence of integral membrane proteins were determined by high performance liquid chromatography (HPLC). Electrophoresis was used to determine the surface charge density of the rat liver cell membranes. Ethanol increased phospholipid levels and altered the level of integral proteins as determined by decreased phenylalanine (Phe), cysteine (Cys) and lysine (Lys). Ethanol significantly enhanced changes in the surface charge density of the liver cell membranes. l-Carnitine administration to ethanol-intoxicated rats significantly protects phospholipids and proteins against oxidative modifications. Therefore, the beneficial effect of l-carnitine may be connected to its ability to scavenge free radicals.