Search PubMed⌕ Search

Biomedical subjects

G Kramer

Publications and source records attributed to G Kramer.

At least 181 records · Page 10Linked to original sources
PubMed1981

Position of transfer ribonucleic acid on Escherichia coli ribosomes. Distance from the 3' end of 16S ribonucleic acid to three points on phenylalanine-accepting transfer ribonucleic acid in the donor site of 70S ribosomes.

Escherichia coli 16S RNA from 30S ribosomal subunits was isolated, oxidized at the 3' end, and labeled with the thiosemicarbazide derivatives of fluorescein or eosin. Labeled 16S RNA was reconstituted into 30S subunits. They were almost fully active compared to 30S subunits reconstituted from unlabeled 16S RNA by using a poly(uridylic acid)-directed polyphenylalanine synthesis assay. Fluorophores were placed at three different positions of tRNAPhe. E. coli and yeast tRNAPhe were oxidized at the 3' end and labeled with the thiosemicarbazide derivative of fluorescein or with the hydrazide of N-methylanthranilic acid. The Y base in the anticodon loop of yeast tRNAPhe was replaced by proflavin or 1-aminoanthracene. Also, E. coli tRNAPhe was photochemically cross-linked between 4-thiouridine at position 8 and cytidine at position 13. After reduction, this site was used as a fluorescent probe. The labeled tRNAs were bound into the peptidyl site of 70S ribosomes, and then the distances from the fluorophore in the modified tRNA to the fluorophore at the 3' end of 16S RNA were measured by nonradiative energy transfer. Calculations were based on measurements of fluorescence lifetimes. The distances to the 3' end of 16S RNA were found to be as follows: 3' end of tRNA, 67-74 A; cross-linked t RNA, 53-60 A; anticodon loop of tRNA, greater than 61 A.

Binding Sites↗
PubMed1981

Localization of 3' ends of 5S and 23S rRNAs in reconstituted subunits of Escherichia coli ribosomes.

Periodate-oxidized 3' ends of 5S, 23S, and 16S rRNAs from Escherichia coli were allowed to react with fluorescein thiosemicarbazide, then labeled rRNAs were reconstituted into active ribosomal subunits. The fluorescein moiety on each of the rRNAs when reconstituted into ribosomal subunits was accessible to anti-fluorescein IgG as determined by fluorescence quenching and by sucrose gradient centrifugation. The region at which an antibody molecule bond to the labeled ribosomal subunits was determined by immunoelectron microscopy. The 3' end of the 5S RNA was localized on the central protuberance of the 50S subunit. The corresponding region for the 3' end of the 23S RNA was below the stalk on the noninterfacing surface. The 3' end of the 16S RNA was localized to the upper edge of the large lobe of 30S subunits, as reported previously.

Escherichia coli↗
PubMed1980

Distances between 3' ends of ribosomal ribonucleic acids reassembled into Escherichia coli ribosomes.

The three ribonucleic acids (RNAs) from Escherichia coli ribosomes were isolated and then labeled at their 3' ends by oxidation with periodate followed by reaction with thiosemicarbazides of fluorescein or eosin. Ribosomal subunits reconstituted with the labeled RNAs were active for polyphenylalanine synthesis. The distances between the 3' ends of the RNAs in 70S ribosomes were estimated by nonradiative energy transfer from fluorescein to eosin. The percentage of energy transfer was calculated from the decrease in fluorescence lifetime of fluorescein in the quenched sample compared to the unquenched sample. Fluorescence lifetime was measured in real time by using a mode-locked laser for excitation and a high-speed electrostatic photomultiplier tube for detection of fluorescence. The distances between fluorophores attached to the 3' ends of 16S RNA and 5S RNA or 23S RNA were estimated to be about 55 and 71 A, respectively. The corresponding distance between the 5S RNA and 23S RNA was too large to be measured reliably with the available probes but was estimated to be greater than 65 A. Comparison of the quantum yields of the labeled RNAs free in solution and reconstituted into ribosomal subunits suggests that the 3' end of 16S RNA does not interact appreciably with other ribosomal components and may be in a relatively exposed position, whereas the 3' ends of the 5S RNA and 23S RNA may be buried in the 70S ribosomal subunit.

Chemical Phenomena↗
PubMed1980

Partial purification and characterization of a 90,000-dalton peptide involved in activation of the eIF-2 alpha protein kinase of the hemin-controlled translational repressor.

In the absence of heme, a negative translational control system is activated in reticulocytes or their lysates that causes the phosphorylation of the smallest subunit of peptide initiation factor 2 and the inhibition of peptide initiation. Two partially purified enzyme fractions are shown to give a concerted effect for phosphorylation of this subunit of initiation factor 2 and binding of methionyl-tRNAf to 40S ribosomal subunits. One enzyme fraction contains a 90,000-dalton peptide that functions in activation of an enzyme containing a 100,000-dalton peptide of the other fraction. Phosphorylation of the 100,000-dalton peptide is correlated with activation of the kinase for the smallest subunit of initiation factor 2. Antibodies against the 90,000-dalton peptide decrease phosphorylation of both the 100,000-dalton peptide and the subunit of initiation factor 2. The results indicate that at least two components function in a sequence of reactions that inhibits protein synthesis by phosphorylation of the smallest subunit of eucaryotic initiation factor 2. The same sequence may be activated in the presence of heme by a cascade type of reactions initiated by a heat-stable protein, HS [Henderson, A.B., Miller, A.H., & Hardesty, B. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 2605-2609].

Animals↗
PubMed1980

Partial purification and characterization of reticulocyte phosphatase with activity for phosphorylated peptide initiation factor 2.

An enzyme fraction containing phosphatase activity for phosphorylated eukaryotic peptide initiation factor 2 (eIF-2) has been isolated from rabbit reticulocytes and partially characterized. The enzyme efficiently catalyzes release of phosphate from the small subunit of eIF-2 (eIF-2 alpha) that has been phosphorylated by the hemin-controlled repressor. It is shown to restore activity of this phosphorylated eIF-2 for binding of methionyl-tRNAf to 40 S ribosomal subunits in a partial reaction of peptide initiation. The enzyme fraction also has phosphatase activity for eIF-2 phosphorylated in its largest subunit and for the 100,000-dalton peptide associated with the eIF-2 alpha kinase activity of the hemin-controlled repressor. The phosphoprotein phosphatase has been isolated by a procedure involving precipitation with ethanol at room temperature and has an apparent molecular weight in the order of 76,000. Its phosphatase activity for eIF-2 alpha is stimulated about 3-fold by optimal concentrations of Mn2+, but is not stimulated by Ca2+ or Mg2+. The enzyme is strongly inhibited by Fe2+ and by purine nucleoside diphosphates.

Animals↗
PubMed1979

No effect of cAMP on protein synthesis in reticulocyte lysates.

The results of a series of experiments are interpreted to indicate that protein synthesis in reticulocyte lysates is not affected by the reticulocyte cAMP-dependent protein kinase. The catalytic subunit of this enzyme was isolated to apparent homogeneity. Also, the protein inhibitor of this protein kinase was isolated from muscle. Neither physiological concentrations of cAMP nor any of these protein components had a detectable effect on protein synthesis in reticulocyte lysates in the presence or absence of exogenous heme. Phosphorylation of the smallest subunit of eukaryotic initiation factor 2 or the 90,000 to 100,000-dalton peptide associated with eukaryotic initiation factor 2 kinase activity were not affected by the activity of the cAMP-dependent protein kinase under conditions in which exogenous heme has a pronounced effect on these reactions.

Animals↗
PubMed1979

Effects of local anesthesia on gingival cAMP levels.

The basal levels of cAMP in the attached gingiva of Rhesus monkeys and the changes in tissue cAMP levels produced by infiltration anesthesia with lidocaine and lidocaine containing 1:100,000 epinephrine were studied. The basal level of cAMP in uninjected monkey gingiva ranged from 12 to 20 picomoles of cAMP per mg of gingival protein. This level was 75 times greater than the cAMP content of monkey blood plasma. Infiltration of the attached gingiva with saline or plain lidocaine for 5 minutes did not produce any significant changes in tissue cAMP levels. Infiltration of the gingiva with lidocaine containing 1:100,000 epinephrine, on the other hand, caused a very marked increase in tissue cAMP levels. Thirty seconds after infiltration with lidocaine with 1:100,000 epinephrine there was a 250% increase in cAMP content of the anesthetized tissue versus the uninjected control tissues. The maximal increase in tissue cAMP levels was observed 5 minutes after infiltration when the cAMP content of the gingiva was 1000 to 1100% above the control level. It is proposed that regulation of tissue cAMP levels by epinephrine or other agents may prove of therapeutic usefulness in regulating inflammation and healing of tissues after surgery or other trauma.

Anesthesia, Dental↗
PubMed1979

[Operative risk in very old patients (author's transl)].

Patients more than 75 years of age will tolerate surgery with good results under the following conditions: 1) Metabolic deficiencies have to be compensated prior to surgery - 2) Preoperative preparatory treatment should be completed at least 3 days before surgery - 3) After surgery has been performed acid-base balance, haemoglobin, protein metabolism and renal function should be watched strictly - 4) Ambulation of the patient and social care should start on the very first day after surgery.

Acid-Base Imbalance↗
PubMed1978

GTP hydrolysis during methionyl-tRNAf binding to 40 S ribosomal subunits and the site of edeine inhibition.

Three lines of evidence are presented indicating that GTP hydrolysis associated with eukaryotic peptide initiation occurs in the absence of 60 S subunits when methionyl-tRNAf is bound to 40 S ribosomal subunits. An enzyme fraction required for binding of methionyl-tRNAf to 40 S subunits and peptide initiation, tentatively equated with eIF-(4 + 5), has GTPase activity and appears to be responsible for hydrolysis of GTP in the methionyl-tRNAf.eIF-2.GTP complex. Direct analysis of the methionyl-tRNAf.40 S complex formed with with eIF-2 and [8-3H] guanine, [gamma-32P]GTP reveals bound guanine but not gamma-phosphate. Edeine, a peptide antibiotic containing spermidine and beta-tyrosine residues at its COOH terminus and NH2 terminus, respectively, blocks peptide initiation and interferes with binding of methionyl-tRNAf to 40 S ribosomal subunits. Inhibition of binding is observed when the eIF-2-mediated binding reaction is carried out with GTP but not with guanosine 5'-(beta,gamma-methylene)triphosphate or guanosine 5'-(beta,gamma-imido)triphosphate. Edeine was labeled by iodination and shown to bind with high affinity to 40 S but not to 60 S ribosomal subunits. It is suggested that edeine blocks a specific site on the 40 S ribosomal subunit to which a segment of the methionyl-tRNAf molecule is bound during the course of the initiation reaction sequence.

Animals↗
PubMed1978

[Image intensifiers in Osteosynthesis a danger for the team? (author's transl)].

Three years' examination of X-ray load when working with the X-ray image intensifier have led to the conclusion that with a tolerance basis of 100 mrem per week a fluoroscoping time of about 1 hour is tolerable without lead protection with an average fluoroscoping time of 5 minutes for one osteosynthesis. The operating surgeon can carry out about 10 osteosyntheses per week. For the other members of the operating team the X-ray load is significantly lower and, therefore, there are no limits in practice. It must be noted that an exact record of the fluoroscoping time and dose measurements is absolutely necessary.

Female↗