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Biomedical subjects

H Padh

Publications and source records attributed to H Padh.

30 records · Page 2Linked to original sources
PubMed1985

Inhibition of ascorbic acid uptake by endotoxin: evidence of mediation by serum factor(s).

The effect of bacterial endotoxin on the ascorbic acid uptake by 3T6 fibroblasts was studied. Endotoxin inhibited ascorbic acid uptake by fibroblasts in a dose dependent manner. The inhibition by endotoxin takes place only in the presence of unheated serum; decomplementing serum by heat inactivation at 56 degrees C for 30 minutes eliminates endotoxin's inhibitory effect on ascorbic acid uptake. The effect of endotoxin appears to be instantaneous since the inhibition seen in the cells without any preexposure was similar to the cells preexposed to endotoxin for up to 6 hours. Polymyxin B sulfate which is known to bind the lipid A portion of endotoxin did not reverse the inhibition of ascorbic acid uptake caused by endotoxin.

Animals↗
PubMed1984

Studies of the guanylate cyclase of the social amoeba Dictyostelium discoideum.

Observations on the properties of the guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) of the social amoeba Dictyostelium discoideum are reported. On the basis of similarities in kinetic and fractionation properties, it is shown that the activity from vegetative cells and the sixfold higher activity from starved cells appear to be due to the same enzyme. Most of the activity is found to be soluble, and by gel exclusion chromatography a molecular weight of 250,000 has been estimated for this form. As the enzyme shows considerably more activity with Mn+2 than Mg+2, the Km for Mn+2 activation was determined (700 microM), and compared to the levels of total cell Mn+2 (10 microM) and Mg+2 (3mM). These data suggest that Mg+2 is probably the physiological cofactor. A previous report [J. M. Mato, (1979) Biochem. Biophys. Res. Commun. 88, 569-574] that the enzyme is activated about twofold by ATP was confirmed; but contrary to that report, activation by the ATP analog 5'-adenylyl-imidodiphosphate was also obtained. Since this analog does not donate its phosphate in kinase reactions, it is likely that ATP activates the guanylate cyclase by direct binding rather than by phosphorylation. The known in vivo agonist of the guanylate cyclase, cAMP, did not activate the enzyme in vitro, either alone or in various combinations with calcium, calmodulin, ATP, and phospholipids.

Adenosine Triphosphate↗
PubMed1984

Possible role of calcium in periodontal disease.

The uptake of Ca2+ by endotoxin-challenged 3T6 fibroblasts, in vitro, was studied. In recent years, the role of calcium in cell injury ultimately leading to cell death has attracted a fair amount of interest. The purpose of the study was to determine whether the direct toxic action of endotoxin is related to a disturbance in Ca2+ homeostasis. Increased calcium uptake in endotoxin-challenged cells was found to be directly related to the bacterial source and method of extraction of endotoxin, the cell density of the culture and the pH of the medium. The effect of endotoxin on calcium uptake was completely reversed by polymyxin B which is known to neutralize the endotoxicity of lipopolysaccharides. These results imply that the increased calcium uptake may be one of the mechanisms by which endotoxin causes direct tissue damage. The potential significance of these data to periodontal disease is discussed.

Animals↗
PubMed1983

Forskolin does not activate cyclic AMP synthesis in Dictyostelium discoideum in vivo or in vitro.

Cyclic AMP (cAMP) has been postulated to regulate many of the events in the development of the eukaryotic social ameba Dictyostelium discoideum. The various suggested roles of cAMP could be tested were it possible to reversibly elevate cAMP levels in the organism. To this end we examined the effect of forskolin, which activates the adenylate cyclase of many eukaryotic organisms. We found, however, that the drug does not elevate cAMP levels in intact D. discoideum. In addition, it does not stimulate the adenylate cyclase in either its basal state or activated state.

Adenylyl Cyclases↗
PubMed1980

Lack of adenosine-3',5'-monophosphate receptor protein and apparent lack of expression of adenosine-3',5'-monophosphate functions in Mycobacterium smegmatis CDC 46.

The presence of adenosine-3',5'-monophosphate (cAMP), adenylate cyclase and the effect of glucose on cAMP levels in Mycobacterium spp have been reported earlier. To understand the role(s) of cAMP in these organisms, the induction of various enzyme systems was studied. Beta-galactosidase and L-tryptophanase were present at low levels of activity and could not be induced. Glycerokinase was inducible but the induction was not affected by glucose. The fructose uptake system was inducible, and the induction was lowered in the presence of glucose, but cAMP could not reverse the inhibition. cAMP binding protein was not detectable under a variety of conditions. On the basis of the lack of active cAMP binding protein, a model has been proposed to explain the apparent lack of expression of cAMP function in Mycobacterium smegmatis CDC 46.

Carrier Proteins↗
PubMed1976

Adenosine 3',5'-monophosphate in Mycobacterium phlei and Mycobacterium tuberculosis H37Ra.

Adenosine 3',5'-monophosphate (cAMP) is present in slow growing as well as fast growing mycobacteria. Apparently there does not seem to be any direct relationship between either intra- or extracellular cAMP content with the growth rate of bacilli. As compared to that of E. coli grown on a similar energy source, cAMP content is much higher in mycobacteria. cAMP content inside the cells remains unaltered throughout the growth period and this may be due to lack of complete utilization of the major energy source, glycerol. Glucose when added to the cells, suspended in phosphate buffer, caused a remarkable decrease in intracellular cAMP content, a phenomenon well established in other bacteria.

Asparagine↗