Search PubMed⌕ Search

Biomedical subjects

M Li

Publications and source records attributed to M Li.

At least 1,153 records · Page 64Linked to original sources
PubMed1987

Enzymatic mechanisms in the metabolic activation of N-nitrosodialkylamines.

The metabolism of several N-nitrosodialkylamines was studied using rat liver microsomes and purified cytochrome P450 isozymes in a reconstituted monooxygenase system. With purified acetone/ethanol-inducible cytochrome P450 (P450ac), high N-nitrosodimethylamine (NDMA) demethylase activity was observed. Cytochrome b5 was also involved in NDMA metabolism by decreasing the Km of NDMA demethylase. A close relationship between the demethylation and denitrosation of this substrate was observed. P450ac was also active in the metabolism of N-nitrosoethylmethylamine (NEMA), but was less active than phenobarbital-inducible cytochrome P450 (P450b) in the metabolism of N-nitrosobutylmethylamine (NBMA), especially in catalysing the debutylation reaction. Similar substrate specificity was demonstrated with liver microsomes from rats treated with other inducers. With different P450 isozymes and microsomes, a close relationship between metabolism and activation of nitrosamines to mutagens to V79 cells was demonstrated. DNA alkylation by NDMA in vitro was correlated with the rate of metabolism of these compounds, whereas DNA alkylation in vivo was more complex and was dose-dependent. The work demonstrates the importance of knowledge of the substrate specificity of cytochrome P450 isozymes in understanding the mechanisms of the metabolic activation of nitrosamines.

Animals↗
PubMed1986

Structural studies on rhodilunancins A and B.

Antitumor antibiotics rhodilunancins A and B were isolated from a culture of Streptomyces violaceus var. lunanensis var. n. No. 1289 by acidic acetone extraction of mycelia and purified by silica gel chromatography. Rhodilunancin A is identical to cosmomycin A. Rhodilunancin B is identical to cosmomycin B (= rhodomycin Y). Both antibiotics exhibited activities against Gram-positive bacteria and inhibition on DNA synthesis of P388 leukemia cell in vitro.

Anthracyclines↗
PubMed1981

Fundus photocoagulation with the argon and krypton lasers: a comparative study.

Photocoagulation of the monkey fundus with an argon-krypton laser photocoagulator was performed. Lesions produced by argon and krypton wavelengths were compared at various power settings, spot sizes, and exposure durations. At low energy levels argon laser lesions appeared clinically stronger than those produced by the krypton mode. Lesions in the foveal area produced with the argon laser demonstrated more extensive microscopic damage to the inner retinal layers than did those produced with the krypton laser. Histologically, both modalities affected the outer layers of the retina. However, the krypton wavelength affected more of the choriocapillaries and the larger choroidal vessels than the argon wavelengths. Conversely, argon laser coagulation of the retinal vessels damaged the perivascular tissue in the nerve fiber layer more than the krypton laser did. Rupture of Bruch's membrane and choroidal hemorrhage occurred frequently with the krypton laser at low energy levels when a small spot size and a short coagulation time were used. Both complications were less likely to occur with argon burns at similar dosage parameters. By choosing larger spot sizes and longer coagulation times for the krypton laser, these complications were prevented.

Animals↗
PubMed1980

Codon recognition rules in yeast mitochondria.

The mitochondrial genome of Saccharomyces cerevisiae codes for 24 tRNAs. The nucleotide sequences of the tRNA genes suggest a unique set of rules that govern the decoding of the mitochondrial genetic code. The four codons of unmixed fmilies are recognized by single tRNAs that always have a U in the wobble position of the anticodon. The codons of the mixed families are read by two different tRNAs. Codons terminating in a C or U are recognized by tRNAs with a G and codons terminating in a G or A are recognized by tRNAs with a U in the corresponding positions of the anticodons. There are two exceptions to these rules. In the AUN family for isoleucine and methionine, the isoleucine tRNA has a G and the methionine tRNA has a C in the wobble position. The tRNA for the arginine CGN family also has an A in the wobble position of the anticodon. It is of interest that the CGN codons have not been found in the mitochondrial genes sequenced to date. The simplified decoding system of yeast mitochondria allows all the codons to be recognized by only 24 tRNAs.

Anticodon↗