Cellular receptors for type beta transforming growth factor. Ligand binding and affinity labeling in human and rodent cell lines

Type beta transforming growth factor (beta TGF) purified from human platelets to homogeneity as judged by NH2-terminal amino acid sequence analysis has been labeled with 125I to characterize its interaction with cellular receptors. Binding of 125I-beta TGF to target cells is temperature- and time-dependent, specific, saturable, and reversible. About 1.6-1.9 X 10(4) binding sites/cell with high affinity for beta TGF (Kd = 5.6-7.8 X 10(-11) M and 9.1-14 X 10(-11) M, respectively) are found in NRK-49F and BALB/c 3T3 cells. beta TGF receptors do not appear to undergo acute down-regulation by the ligand. Specific binding of 125I-beta TGF has been observed in several human, rat, and mouse fibroblast lines and in some, but not all, tumor-derived cell lines examined. 125I-beta TGF has been cross-linked to intact cells and isolated membrane preparations using disuccinimidyl suberate. Cells and isolated membranes from human, rat, and mouse origin affinity labeled with 125I-beta TGF exhibit a major labeled species of approximately 280 kilodaltons that has the properties of high affinity and specificity expected from a physiologically relevant beta TGF receptor. Minor labeled species of 70-90 kilodaltons are also labeled by 125I-beta TGF, but they correspond to molecular species with low apparent affinity (Kd approximately 10(-8) M) for 125I-beta TGF.     

Changes in the electrophoretic pattern of the venom of the bushmaster (Lachesis muta stenophrys) stored under various conditions

Liquid and lyophilized samples of Lachesis muta venom were stored at different temperatures and for different periods of time, and analyzed by polyacrylamide gel electrophoresis (PAGE) and immunoelectrophoresis. Only slight variations were evident when three pools of freeze-dried venom, that had been kept at -30 degrees C for several months were compared with fresh venom. These results suggest that L. muta venom is not altered drastically when stored under these conditions.     

Respiratory effects of naloxone

The respiratory effects of naloxone (200 micrograms X kg-1) on dogs, was studied measuring the parameters breath rate, inspiratory volume, breath minute volume, inspiratory time, total time of cycle, inspiratory volume/inspiratory time ratio, and inspiratory time/total time of cycle ratio. The statistical study was made by using the analysis of variance. Naloxone increases all the parameters studied as well as the response to CO2 while it decreases inspiratory time. The results suggest that there are opioid neurons in the respiratory centre. The blockade of the opioid receptors by naloxone almost explains the respiratory effects observed.     

Effect of naloxone on coughing

Naloxone at doses of 200 micrograms X kg-1 increases cough, in experiments carried out on dogs. With stimuli of the same intensity, after naloxone, a significant increase in the number of coughs in each fit, is observed. Changes in the first cough burst, compared with spontaneous respiration at rest, are statistically significant and they contribute to define the characteristics of the cough burst. The increase of cough by naloxone blockade of endorphinic neurons of the respiratory center shows that usually the activity of these inhibitory neurons, tonically depresses the tussive response. The antitussive opiates would seem to operate by activating these inhibitory synapses.     

Stimulation of intestinal adenylate cyclase by cholera toxin in malnourished rats

The stimulation of intestinal adenylate cyclase by cholera toxin (CT) was studied in normal and malnourished rats 4 to 24 hr after a 30-min incubation of intestinal loops with the toxin. Whereas in control rats the enzyme activity returned to basal levels after 12 hr of incubation, in malnourished rats the activity of the enzyme remained significantly elevated even after 24 hr of the initial incubation. Malnourished animals had a reduced turnover rate of intestinal cells as determined by thymidine kinase activity. The delayed turnover of intoxicated cells may account for continuous activation of mucosal adenylate cyclase and possibly for prolongation of diarrhea in malnutrition.     

Synthesis and molecular structure of prolame, N-(3-hydroxy-1,3,5(10)-estratrien-17 beta-yl)-3-hydroxypropylamine; an amino-estrogen with prolonged anticoagulant and brief estrogenic effects

The synthesis and molecular structure of prolame, N-(3-hydroxy-1,3,5(10)-estratrien-17 beta-yl)-3-hydroxypropylamine, is described. It was characterized by ir, nmr, mass spectrometry and chemical analysis. The crystal structure of this compound was determined by single-crystal x-ray diffraction. Prolame belongs to space group P212121. Cell dimensions are: a = 8.356(2), b = 13.343(4) and c = 16.119(4) A. Z = 4; R = 4.1%.     

Isoproterenol induces a ribosomal modification in the heart and the skeletal muscle of hamsters

The protein synthesis activity of heart, skeletal muscle and liver polysomes from isoprotenerol-treated and control hamsters has been compared in an in vitro non-inititating translation system. Heart and skeletal muscle polysomes from treated hamsters were less active than controls and required a higher magnesium concentration for optimal protein synthesis. These results suggest that there is a conformational modification in heart and skeletal muscle ribosomes from isoprotenerol-treated hamsters. No such change was observed with ribosomes from the liver of isoproterenol-treated hamsters.     

The steady-state rate equation for cytochrome c oxidase based on a minimal kinetic scheme

A minimal catalytic cycle for cytochrome c oxidase has been suggested, and the steady-state kinetic equation for this mechanism has been derived. This equation has been used to simulate experimental data for the pH dependence of the steady-state kinetic parameters, kcat and Km. In the simulations the rate constants for binding and dissociation of cytochrome c and for two internal electron-transfer steps have been allowed to vary, whereas fixed experimental values (for pH 7.4) have been used for the other rate constants. The results show that the dissociation of the product, ferricytochrome c, cannot be rate-limiting under all conditions, but that intramolecular electron-transfer steps also limit the rate. They also demonstrate that Km can differ considerably from the dissociation constant for the cytochrome c-oxidase complex. Published values for the rate constant for the dissociation of ferricytochrome c are too small to account for the steady-state rates. It is suggested that, at high concentrations, ferryocytochrome c transfers an electron to a cytochrome c molecule which remains bound to the oxidase. This can also explain the nonhyperbolic kinetics, which is observed at low substrate concentrations.     

Total biodegradation of 4-chlorobiphenyl (4 CB) by a two-membered bacterial culture

Summary Several bacterial strains that can oxidize mono- and dichlorinated biphenyls with one unsubstituted ring have already been described. The major route for this biodegradation leads ultimately to the corresponding chlorobenzoic acid, but several other minor chlorinated metabolites that might possibly be of concern for the environment have also been described previously. Since none of the bacterial strains that are able to oxidize these chlorinated biphenyls in pure culture are known to degrade chlorobenzoic acid, the oxidation of these substrates by axenic cultures always generates chlorobenzoates plus several other metabolites. In the present study, we have estimated the biodegradation of 4-chlorobiphenyl (4CB) by a two-membered bacterial culture containing one strain able to grow on 4CB and to transform it into 4-chlorobenzoate (4CBA) and one strain able to degrade 4CBA. The results were encouraging, since it was shown that the degradation of 4CB was more rapid and complete with the double bacterial culture.