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Biomedical subjects

E Borek

Publications and source records attributed to E Borek.

At least 55 records · Page 3Linked to original sources
PubMed1976

Beta-aminoaciduria in patients with Burkitt's lymphoma.

The massive amounts of beta-aminoisobutyric acid (beta-AIBA) in the urine of Burkitt's lymphoma patients were measured along with other alpha-amino acids and beta-alanine present in normal and decreased levels. The ratios of the amount of beta-AIBA to beta-alanine, in mumoles/kg urine collected in 24 hours, were elevated for all patients. The degree of elevation of beta-AIBA excretion and the ratio of the two beta-amino acids appeared to be related to the amount of tumor mass present. These analyses may have possible value in monitoring patients with Burkitt's lymphoma during their disease course.

Alanine↗
PubMed1976

Changes in transfer RNA's in human malignant trophoblastic cells (BeWo line).

Ten aminoacyl transfer RNA's prepared from human malignant trophoblastic cells (BeWo line) were compared with the corresponding aminoacyl transfer RNA's from normal human chorionic tissue by cochromatography on a RPC-5 column. Phenylalanyl transfer RNA (Phe-tRNA) of BeWo cells had, in addition to the single species of Phe-tRNA found in normal chorionic tissues, an early eluting component. When Phe-tRNA from the chorion was exposed to mild acid, which selectively excises the Y base, it eluted in the same position as the early eluting Phe-tRNA of BeWo cells. Therefore, the BeWo Phe-tRNA is partially undermodified. Tyrosyl transfer RNA of BeWo cells exhibited a broad-based peak which eluted later than the normal and probably consists of two or more tyrosyl transfer RNA's. Seryl transfer RNA of BeWo cells showed two peaks of acceptor activity, while seryl transfer RNA of normal chorion had a third peak that eluted at a higher salt concentration. In addition, in an early eluting methionyl and lysyl transfer RNA and in a late eluting arginyl transfer RNA from BeWo cells and normal charion, quantitative alterations were detected. The remaining four transfer RNA's, leucyl, aspartyl, valyl, and histidyl, from the two sources did not show any significant differences in elution profiles. These alterations of the chromatographic profile appeared to be due to new or altered species of transfer RNA. They were not due to differences in the aminoacyl transfer RNA synthetase. The transfer RNA methyltransferase capacity of the enzymes from BeWo cells was 2-fold higher than that of the enzymes extracted from the chorion.

Amino Acids↗
PubMed1976

A mechanism of estrogen action on gene expression at the level of translation.

One of the earliest events following the administration of estradiol to ovariectomized rats is an increase in transfer RNA (tRNA) methyltransferase activity activity of the uterus. Ovariectomy diminishes by about one-half the capacity of extracts of uteri to introduce methyl groups in vitro into heterologous tRNA. Administration of estradiol to ovariectomized animals restores the tRNA methyltransferase capacity to normal. Alterations in the population of uterine serine tRNA were also observed following ovariectomy. These findings represent reversible qualitative changes produced by a hormone in the target tissue. Whether the tRNA's are involved in regulating hormone-induced protein synthesis was investigated by studying the estrogen-induced ovalbumin synthesis in immature chick oviducts. tRNA's from oviducts of estrogen-stimulated chicks or from oviducts of laying hens produced an enhanced stimulation of ovalbumin synthesis in vitro compared with tRNA's from oviducts of immature chicks that were withdrawn from estrogen stimulation (these chicks do not synthesize ovalbumin). Some of these hormone-induced alterations may be of importance in understanding the molecular mechanisms of estrogen action on gene expression. During these studies, we have observed a novel effect of the administration of the carcinogen, ethionine, in the immature chicks. Ethionine induces ovalbumin and conalbumin synthesis in immature chick oviducts that were withdrawn from estrogen for 3 to 4 weeks following primary estrogen stimulation.

Animals↗
PubMed1975

A transfer RNA-dependent protein synthesizing system from Ehrlich ascites extracts.

An homologous cell-free system from Ehrlich ascites cells was made tRNA dependent by passing both the ribosomes and the ammonium sulfate fraction through DEAE-cellulose columns in 0.30 M KCl. Protein synthesis was routinely stimulated 20-50 fold by the addition of 100 mug/ml of ascites cell tRNA in the presence of oviduct mRNA, ascites mRNA, or encephalomyocarditis RNA.

Animals↗
PubMed1975

Functional differences in protein synthesis between rat liver tRNA and tRNA from Novikoff hepatoma.

Synthesis of ovalbumin in fragmented oviduct magnum explants of immature, estrogen-stimulated chicks has been studied in the presence of exogenous tRNA. tRAN from Novikoff hepatoma specifically inhibited ovalbumin synthesis, determined by precipitation with antisera. In addition, the major protein(s) synthesized in the presence of hepatoma tRNA had higher electrophoretic mobility than ovalbumin, as shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis. tRNAs from rat liver, rooster liver, and hen oviduct did not affect ovalbumin synthesis, although oviduct tRNA is stimulatory during the earlier stages of estrogen stimulation.

Animals↗