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Biomedical subjects

G Letko

Publications and source records attributed to G Letko.

65 records · Page 4Linked to original sources
PubMed1979

The stimulation of the mitochondrial respiration by citrulline synthesis.

1. The influence of ammonia and ornithine on the oxygen uptake and the formation of citrulline was investigated with isolated rat liver mitochondria. The experiments were performed in a cytosol-like saline medium at 38 degrees C. 2. Under these conditions an increase of the respiration rate by ammonia and ornithine was observed, but a small response to external ADP, only. The missing stimulation by ADP was due to a partial inhibition of the respiratory chain by traces of zinc (approximately 1 microM) present in the medium. This inhibition was only detected at low concentrations of mitochondria. 3. For activation of respiration by ammonia plus ornithine two different processes were responsible: (i) chelation of the inhibiting zinc by ornithine, which could be prevented by EDTA; (ii) ADP production in the matrix space during formation of carbamoyl phosphate, which could be prevented by oligomycin but not by carboxyatractyloside. 4. This stimulus of the carbamoyl phosphate formation and of the equivalent citrulline synthesis on the mitochondrial respiration ran to 12% of that increase caused by phosphorylation of external ADP. The maximum rate of citrulline formation was limited by the activity of carbamoyl phosphate synthetase. 5. Added ADP suppresses the production of citrulline probably by the exchange of extramitochondrial ADP versus intramitochondrial ATP. The data suggest a common adenine nucleotide pool delivering ATP to the adenine nucleotide translocase as well as to the carbamoyl phosphate synthetase.

Animals↗
PubMed1979

Competition between extramitochondrial and intramitochondrial ATP-consuming processes.

The relationship between intra- and extramitochondrial ATP utilization was investigated in liver mitochondria isolated from normally fed, starved and high-protein fed rats. ATP export was provoked by adding a hexokinase-glucose-trap and intramitochondrial ATP consumption by adding ammonia, bicarbonate and ornithine in order to stimulate citrulline synthesis. Both processes compete for ATP produced via oxidative phosphorylation; the rate of citrulline formation declines as the extramitochondrial [ATP]/[ADP] ratio decreases. It is concluded that ATP for adenine nucleotide translocation and that for carbamoyl phosphate synthesis are delivered from a common intramitochondrial pool of adenine nucleotides. In mitochondria from rats with a high-protein diet, citrulline synthesis greatly stimulates the rate of oxidative phosphorylation (about two thirds of state 3 respiration). Under these conditions the intramitochondrial [ATP]/[ADP] ratio is significantly reduced. The intramitochondrial [ATP]/[ADP] ratio is not in thermodynamic equilibrium with the extramitochondrial one.

Adenine Nucleotides↗
PubMed1978

Influence of Mg2+-ions on the properties of rat heart mitochondria in dependence on the preparation.

1. The preparation of rat heart mitochondria with Potter-Elvehjem homogenizer results in mitochondria showing stimualtion of respiration induced by Mg2+. This stimualtion is neither caused by adherent hexokinase nor by energy-dependent magnesium accumulation (Mg2+ content in the presence of 10 mM glutamate: 22 nmoles/mg protein; in the presence of glutamate plus antimycin A 21 nmoles/mg protein). 2. The effect of added magnesium is excluded by addition of carboxyatractyloside. This demonstrates the activity of an ATPase outside of the mitochondrial inner membrane. 3. A simple and rapid method for the preparation of Mg2+-insensitive rat heart mitochondria is presented. The minced heart is pressed through a normal syringe and then treated with trypsin. 4. A comparison of mitochondria of both preparations shows that there is no difference in magnesium content and no energy-dependent magnesium influx.

Adenylate Kinase↗
PubMed1975

Further characterization of the association of glyceraldehyde-3-phosphate dehydrogenase with reticulocyte membranes.

1. The behaviour and properties of membrane-bound GAPDH of rabbit reticulocytes were investigated. 2. The bound GAPDH is more resistant to inactivation by KCl than the soluble enzyme (allotopy). 3. The bound enzyme is released by electrolytes. This effect does not only depend on the ionic strength but additionally on the kind of ions, pH-value and protein concentration. 4. A comparison of the releasing effect of NAD analogues shows the necessity of the 5'-AMP moiety in the structure of the effector. 5. The represented results demonstrate the specifity of the GAPDH-membrane binding in rabbit reticulocytes.

Animals↗
PubMedDate not supplied

Enzymatic and histologic investigations into the course of pancreatic alterations induced by anti-acinar-cell-antiserum.

A model of acute pancreatitis (AP) was developed by application of anti-acinar-cell-antiserum in rats. Within 24 h postoperatively the binding of antibodies to the pancreas, histological findings, and the activities of lipase and a-amylase in serum and pancreas were analyzed. While after intraaortic administration morphological alterations could not be observed, after single dose intraductal injection, typical macroscopical and histological signs of AP were found. This pancreatic injury was characterized by a mild and protracted course favoring investigations of the early phase of pathogenesis. As soon as 2 h after intraductal application of antiserum, serum amylase and lipase were already increased and microscopic examination of the pancreatic tissue revealed pancreatic edema, inflammatory infiltration and parenchymal necrosis. Intra- and extrapancreatic fat necrosis occurred at 16 h post injectionem. The results suggest that parenchymal damage plays an essential role in the manifestation of this experimental AP and that fat necrosis seems to be a secondary event.

Acute Disease↗
PubMedDate not supplied

Experimental acute pancreatitis in rats after chronic and chronic plus acute ethanol administration in combination with a pancreatic juice edema.

The influence of long-term (26 weeks) and long-term plus acute ethanol administration on the development of acute pancreatitis was studied in rats. While both these treatments alone did not induce pancreatitis in any rat, extrapancreatic fat necrosis and histologic lesions of the pancreas were found in the majority of animal 24 hours after additional establishing of a pancreatic juice edema by an obstruction/hypersecretion mechanism. Severity and frequency of findings were significantly increased by additional short-term ischemia (25 min) of the pancreas. In control rats without ethanol ingestion, the edema receded without any lesions, and after additional ischemia significantly fewer rats exhibited signs of acute pancreatitis when compared to the ethanol-treated groups. An experimental model of acute alcoholic pancreatitis is presented with ethanol ingestion, temporary ductal obstruction and stimulation of secretion being essential constituents, which may be of clinical relevance, too.

Acute Disease↗