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Biomedical subjects

J Laval

Publications and source records attributed to J Laval.

At least 109 records · Page 6Linked to original sources
PubMed1981

Release of 7-methylguanine residues from alkylated DNA by extracts of Micrococcus luteus and Escherichia coli.

Cell extracts from Micrococcus luteus release both free 3-methyladenine and free 7-methylguanine from alkylated DNA. The glycosylase activity responsible for the liberation of 7-methylguanine is not 3-methyladenine-DNA glycosylase, which, when purified, does not liberate it. Furthermore, the heat inactivation rates of the two enzymatic activities are different. The release of 7-methylguanine by chemical depurination of ethanol-soluble oligonucleotides has been ruled out. A similar activity releasing 7-methylguanine is also found in Escherichia coli.

Animals↗
PubMed1980

Micrococcus luteus endonucleases for apurinic/apyrimidinic sites in deoxyribonucleic acid. 1. Purification and general properties.

Two chromatographically distinct endonucleases from Micrococcus luteus, specific for apurinic and apyrimidinic sites (AP-endonucleases A and B), have been extensively purified and characterized. Both are free from DNA glycosylase, unspecific endonuclease, and phosphatase activities. The two enzymes behave as monomeric proteins of approximately 35000 daltons. In addition to their different chromatographic properties on CM-cellulose, P-cellulose, hydroxylapatite, and DNA--Sepharose, both AP-endonucleases can be distinguished as follows: AP-endonuclease A has an isoelectric point of 4.8, shows a half-life of 4 min at 45 degrees C, reacts optimally at pH 7.5 and has a KM value of 2.3 X 10(-6) M. AP-endonuclease B has a pI of 8.8, is more stable at 45 degrees C (half-life of 10 min), and reacts optimally between pH 6.5 and pH 8.5; its KM value is 3.7 X 10(-6) M.

Chromatography, DEAE-Cellulose↗
PubMed1980

Micrococcus luteus endonucleases for apurinic/apyrimidinic sites in deoxyribonucleic acid. 2. Further studies on the substrate specificity and mechanism of action.

Two endonucleases specific for DNA-containing apurinic or apyrimidinic sites (AP-endonucleases A and B) have been isolated from Micrococcus luteus and highly purified. These enzymes have no exonuclease activity. Both AP-endonucleases hydrolyze DNA-containing apurinic or apyrimidinic sites at the 5' end of the lesion, thus generating 3'-hydroxyl and 5'-phosphoryl end groups. DNA-containing pyrimidine dimers, introduced at low doses of UV, are not hydrolyzed, whereas DNA-containing lesions, introduced at high doses of UV or by gamma irradiation are nicked by either AP-endonuclease. During hydrolysis of apurinic DNA, neither of the AP-endonucleases acts as a processive enzyme.

DNA, Viral↗
PubMed1979

Comparative effects of CCK-PZ on certain intestinal hydrolases in the mucosa and in the luminal content of the hamster jejuno-ileum.

After isolation of the hamster small intestine, the effects of a continuous infusion of cholecystokinin-pancreozymin (CCK-PZ) are studied. Several enzymic activities are measured in the intestinal lumen and compared with the level found in the intestinal homogenate. During CCK-PZ infusion we observed a direct stimulation of Paneth cells associated with an increase of lysozyme activity. Furthermore this work confirms the stimulating effect of CCK-PZ on alkaline phosphatase and amino-peptidase. Maltase and sucrase levels were unaffected. The liberation of the hydrolase of the brush border in the intestinal lumen is negligible and cannot be considered as a true secretion. Only granule content of Paneth cells is actually secreted. However, biochemical data, corroborated by morphological results, suggest that Paneth cell secretion could in part be absorbed on the outer surface of the brush border.

Alkaline Phosphatase↗
PubMed1977

Secretion of labelled proteins by the isolated dog pancreas in the response to secretin and cholecystokinin.

We compared the effects of secretin (10 clinical units/hur.) and cholecystokinin-pancreiozymin (CCK-PZ 10 Ivy units/hr.) from G.I.H. Laboratory in Stockholm, Sweden, on the secretion of radioactively labelled proteins in the pancreatic juice. This was carried out on isolated dog pancreas perfused "ex-vivo" with whole heparinized oxygenated blood. CCK-PZ and secretin were infused together and the results compared with a second series of experiments where secretin alone was administered, at the same dose. Both hormones caused a discharge of labelled proteins, which was linear over 55 minutes. Secretin increased the flow rate of the pancreatic juice and to a lesser extent the enzymatic protein output. CCK-PZ stimulated the mass flow of secretory proteins.

Animals↗