Biomedical subjects

F J Lee

Publications and source records attributed to F J Lee.

42 records · Page 3Linked to original sources

PubMed1989

N alpha acetylation is required for normal growth and mating of Saccharomyces cerevisiae.

Acetylation is the most frequently occurring chemical modification of the alpha-NH2 group of eucaryotic proteins and is catalyzed by N alpha-acetyltransferase. The yeast enzyme is encoded by the AAA1 (amino-terminal alpha-amino acetyltransferase) gene. A null mutation (aaa1-1) created by gene replacement, while not lethal, slows cell growth and results in heterogeneous colony morphology. In comparison with wild-type cells, aaa1-1/aaa1-1 diploids cannot enter stationary phase, are sporulation defective, and are sensitive to heat shock. In addition, the aaa1-1 mutation specifically reduces mating functions of MATa cells. These results indicate that N alpha acetylation plays a crucial role in yeast cell growth and mating.

Acetylation↗

PubMed1988

Purification and characterization of an N alpha-acetyltransferase from Saccharomyces cerevisiae.

N alpha-Acetyltransferase, which catalyzes the transfer of an acetyl group from acetyl coenzyme A to the alpha-NH2 group of proteins and peptides, was isolated from Saccharomyces cerevisiae and demonstrated by protein sequence analysis to be NH2-terminally blocked. The enzyme was purified 4,600-fold to apparent homogeneity by successive purification steps using DEAE-Sepharose, hydroxylapatite, DE52 cellulose, and Affi-Gel blue. The Mr of the native enzyme was estimated to be 180,000 +/- 10,000 by gel filtration chromatography, and the Mr of each subunit was estimated to be 95,000 +/- 2,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme has a pH optimum near 9.0, and its pI is 4.3 as determined by chromatofocusing on Mono-P. The enzyme catalyzed the transfer of an acetyl group to various synthetic peptides, including human adrenocorticotropic hormone (ACTH) (1-24) and its [Phe2] analogue, yeast alcohol dehydrogenase I (1-24), yeast alcohol dehydrogenase II (1-24), and human superoxide dismutase (1-24). These peptides contain either Ser or Ala as NH2-terminal residues which together with Met are the most commonly acetylated NH2-terminal residues (Persson, B., Flinta, C., von Heijne, G., and Jornvall, H. (1985) Eur. J. Biochem. 152, 523-527). Yeast enolase, containing a free NH2-terminal Ala residue, is known not to be N alpha-acetylated in vivo (Chin, C. C. Q., Brewer, J. M., and Wold, F. (1981) J. Biol. Chem. 256, 1377-1384), and enolase (1-24), a synthetic peptide mimicking the protein's NH2 terminus, was not acetylated in vitro by yeast acetyltransferase. The enzyme did not catalyze the N alpha-acetylation of other synthetic peptides including ACTH(11-24), ACTH(7-38), ACTH(18-39), human beta-endorphin, yeast superoxide dismutase (1-24). Each of these peptides has an NH2-terminal residue which is rarely acetylated in proteins (Lys, Phe, Arg, Tyr, Val, respectively). Among a series of divalent cations, Cu2+ and Zn2+ were demonstrated to be the most potent inhibitors. The enzyme was inactivated by chemical modification with diethyl pyrocarbonate and N-bromosuccinimide.

Acetyltransferases↗

PubMed1985

Biosynthesis of superoxide dismutase in Saccharomyces cerevisiae: effects of paraquat and copper.

Growth of Saccharomyces cerevisiae in the presence of paraquat caused an increase the intracellular flux of superoxide radicals and in superoxide dismutase biosynthesis. The addition of copper to the growth medium also elicited an increase in superoxide dismutase levels. A cytochrome c deficient mutant strain was found to be more responsive than the wild type strain to paraquat and/or copper by increasing its copper-zinc superoxide dismutase. Catalase activity in both strains was not significantly affected by paraquat and/or copper.

Catalase↗

PubMed1981

The specific binding of androgens and the subsequent distribution of androgen-receptor complexes within MCF-7 human breast cancer cells.

Using a whole cell suspension assay technique, we have examined both the specific binding of testosterone (T) and dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) (DHT) and the subsequent distribution of androgen binding activity within MCF-7 human breast cancer cells. We have observed that both androgens are bound with high affinity to the same single class of receptor which is present at a concentration of approximately 8,000 sites per cell. The incubation of cells with either T or DHT was followed by the nuclear accumulation of specifically bound ligand which increased to maximal values within 1 h and then decreased thereafter. However, only about 30% of the total cellular specific binding activity observed with either androgen was localized within the nuclear compartment at any time during a 4 h incubation. Further examination of the extranuclear binding component suggested that a substantial portion of this activity was localized to the particulate fraction of the cytoplasm. The results of these studies suggest that both T and DHT are capable of exerting biological activity within MCF-7 cells, and raise the interesting possibility that androgen-receptor complexes may participate in the direct regulation of mitochondrial and/or microsomal function in this system.

Breast Neoplasms↗

PubMed1975

Sequential therapy for advanced ovarian adenocarcinoma: operation, chemotherapy, second-look laparotomy, and radiation therapy.

In an attempt to improve the survival rates in women with advanced ovarian adenocarcinoma (abdominal spread), they were treated with sequential therapy. This consisted of operation followed by chemotherapy, second-look exploratory laparotomy, and finally whole-abdomen irradiation. Only those patients who had a complete clinical response to chemotherapy and subsequently underwent a second operation and irradiation were evaluated. Seventy-five per cent of the patients had recurrent cancer within the treated area after sequential therapy was completed. Morever, of four patients with no gross residual cancer after the second operation, three had cancer recurrences within the treated area. It is concluded that methods of treating advanced ovarian adenocarcinoma other than sequential therapy must be found.

Adenocarcinoma↗

PubMedDate not supplied

Use of cryopreserved hepatocytes for unscheduled DNA synthesis assays.

Hepatocytes were isolated from Fischer rats by perfusion and tested for unscheduled DNA synthesis (UDS) induction or cryopreserved for long-term storage at -196 degrees C. Thawed cells could be recovered at greater than 90% viabilities, and were cultured on fibronectin-coated coverslips. The cells attached and spread, and could be used for UDS assessment. Data were compared for fresh and frozen cells from the same animal. Results obtained for net nuclear grains and dose response were similar for the fresh and frozen cells, in response to the carcinogenic compounds methyl methanesulfonate and 7,12-dimethylbenzanthracene, benzo[a]pyrene, and N-methyl-N'-nitro-N-nitrosoguanidine.

Animals↗