PubMed Health⌕ Search

Biomedical subjects

J Hradec

Publications and source records attributed to J Hradec.

At least 109 records · Page 6Linked to original sources
PubMed1980

Particulate aminoacyl-tRNA synthetases are retained on heparin bound to Sepharose.

Fractions of reticulocyte lysates were retained on heparin immobilized on Sepharose 4B and further separated by gel filtration on Sepharose 6B. These fractions contain aminoacyl-tRNA synthetases for 12 amino acids tested. Most synthetases with the highest specific activity are present in the fraction of approximately 40S. Particulate synthetases present in the postmicrosomal pellet of rat liver and synthetases associated with polyribosomes are almost completely adsorbed on heparin-Sepharose but free enzymes in the cytosol are not retained. Since only particulate synthetases are retained on the affinity carrier, their adsorption may be due to the presence of protein-synthesis factors, in particular peptide initiation and elongation factors, in the complexes of synthetases.

Amino Acyl-tRNA Synthetases↗
PubMed1980

Incorporation of labelled amino acids into proteins, from rabbit reticulocytes, retained on heparin-sepharose.

Fractions of rabbit reticulocyte lysates retained on heparin-Sepharose 4B catalyze incorporation of labelled amino acids into proteins in the absence of ribosomes, and several characteristics of this reaction are identical with peptide bond formation mediated by aminoacyl-tRNA-protein transferases. At least five different proteins become labelled, as revealed by polyacrylamide gel electrophoresis. Active fractions synthesize aminoacyl-tRNA which is utilized by transferase. Aminoacyl-tRNA-protein transferase activity may be uncoupled from that of aminoacyl-tRNA synthetase by puromycin or lysyl-phenylalanine which both inhibit the transferase activity only. Adenosine and phosphate inhibit aminoacyl-tRNA synthetase as well as the incorporation of labelled amino acids into proteins. This indicates that the incorporation must be preceded by charging of tRNA with amino acids. Presence of three different aminoacyl-tRNA-protein transferases, each of them specific for a group of four amino acids, was demonstrated. Serum albumin stimulates the incorporation of amino acids and a labelling of this protein was demonstrated in mixtures into which it had been added. Addition of both ribosomal subunits and globin messenger ribonucleoprotein significantly changes the pattern of labelled proteins, and synthesis of globin was demonstrated by polyacrylamide gel electrophoresis. Density-gradient analysis revealed formation of a 48 S ribosomal complex and the formation of polyribosomes. Systems composed of active fractions retained on heparin-Sepharose supplemented with ribosomes and globin messengers apparently catalyze the translation of this message, but interactions do exist between the ribosome-mediated peptide synthesis and non-ribosomal incorporation of amino acids into proteins.

Acyltransferases↗
PubMed1980

Cholesteryl esters are bound by a peptide-initiation and a peptide-elongation factor.

Significantly higher quantities of cholesteryl 14-methylhexadecanoate than of cholesteryl laurate and cholesteryl palmitate are bound by a homogeneous peptide-initiation factor and purified peptide-elongation factor 1. Cholesteryl 14-methylhexadecanoate may function as a specific allosteric modifier changing the conformation of protein synthesis factors and thus modulating the activity of their binding sites.

Binding Sites↗
PubMed1980

Purification and some properties of a cholesterol esterase from rat liver.

A cholesterol esterase operating at a slightly alkaline pH was purified to electrophoretic homogeneity from rat liver cytosol. The enzyme has a molecular weight of 260 000 and is composed of four active subunits of identical molecular weight. The purified enzyme is not able to synthesize cholesteryl esters. Trihydroxy bile salts are absolutely required for the hydrolysis of cholesteryl esters and apparently convert enzyme tetramers into active monomers. They may regulate the esterase activity by maintaining a balance between enzyme monomers and polymers the synthesis of bile acids.

Animals↗
PubMed1980

The advantage of the use of echocardiographic evaluation in hypothyroid patients.

Authors examined 10 patients with untreated myxoedema. The disease lasted at least one year in seven cases. The etiology of disease was autoaggressive thyroiditis in 9 cases and was diagnosed by a high titre of antibodies against thyroglobulin. The levels of T4 and T3 were low in all cases, level of TSH was elevated. The mean level of T4 was 0.91 microgram/dl, of T3 43.5 ng/dl. The level of TSH was over 96 microU/ml in 7 cases, in rest over 54 microU/ml. In all cases ECHO examination was done: pericardial effusion was proved in 80%. 5 patients were followed during substitutional therapy. Clinical signs and laboratory test normalised in all 5 cases. ECHO finding improved: left ventricular SEF from 54.4 +/- 7.4% to 67.9 +/- 10.3%, Vcf 0.82 +/- 16 circ/sec to 1.32 +/- 0.37 circ/sec max PWVs from 43.8 +/- 6.8 mm/sec to 63.2 +/- 9.9 mm/sec. The etiology of myxoedema may play a role in the incidence of pericardial effusion either by influence of autoaggressive disease or, which seems more probable, by a complete failure of thyroid gland secretion with low not only T4 but T3, too. T3 receptors are supposed to play an important role in the myxoedema heart disease.

Adult↗
PubMed1979

Purification and some properties of a protein factor binding and deacylating initiator transfer ribonucleic acid.

1. A protein factor promoting the binding of initiator tRNA to the 40S ribosomal subunit was purified to homogeneity (more than 2500-fold) from rat liver cytosol. It has a mol.wt. of 265000 and is composed of four subunits of identical molecular weight. 2. This factor directs the binding of methionyl-tRNA(fMet) and to a lesser extent also of N-acetylphenylalanyl-tRNA, but not of methionyl-tRNA(Met) or phenylalanyl-tRNA, to the smaller ribosomal subunit at high concentrations of GTP (8-10mm) with an optimum at pH4.0. As evidenced by sucrose-density-gradient centrifugation, initiator tRNA becomes bound to the 40S subunit or to 80S ribosomes. 3. A deacylase activity specific for methionyl-tRNA(fMet) is associated with the pure factor. The factor significantly stimulates the translation of natural message in systems containing polyribosomes and both purified peptide-elongation factors. 4. The factor binds initiator tRNA or GTP to form unstable binary complexes and forms a ternary complex with methionyl-tRNA(fMet) and GTP. This complex is relatively stable. 5. In the absence of any cofactors the factor forms a stable complex with 40S and 80S ribosomes. This preformed ribosomal complex binds efficiently initiator tRNA at pH7.5 and low concentrations of GTP (1-2mm). The ternary complex of the factor with methionyl-tRNA(fMet) and GTP may be liberated from this ribosomal complex. 6. A protein factor capable of promoting the binding and simultaneously the deacylation of initiator tRNA may apparently have a regulatory function in physiological gene translation by removing an excess of methionyl-tRNA(fMet) not required for translation.

Animals↗
PubMed1979

Natriuretic and kaliuretic effect of melanocyte-stimulating hormones in hamsters.

The effect of synthetic melanocyte-stimulating hormones (MSH) on urinary excretion of sodiu, potassium and water was studied in hamsters. Synthetic alpha-MSH and synthetic human beta-MSH showed a marked natriuretic and diuretic effect depending on the dosage of hormone. The natriuretic effect of both hormones was approximately equal and did not parallel the magnitude of the melanocyte-stimulating activity of the investigated peptides. Both peptides showed also a milder kaliuretic effect independent on their dose. The rise of the sodium/potassium index in urine was significant after both peptides. Bilateral adrenalectomy increased further the natriuresis induced by alpha-MSH, while it did not affect the effect o MSH on diuresis and kaliuresis. Changes in urinary excretion of sodium and potassium are considered to be consequence of direct renal action of MSH.

Adrenalectomy↗
PubMed1979

Biosynthesis of cholesteryl 14-methylhexadecanoate in the liver of rats bearing transplantable tumors and during chemical carcinogenesis.

Biosynthesis of cholesteryl 14-methylhexadecanoate, cholesteryl palmitate and cholesteryl stearate was studied in the liver of rats bearing the Walker 256 carcinoma. Zajdela hepatoma and during chemical carcinogenesis following the administration of benzo[a]-pyrene. An up to 9-fold enhanced production of all these esters was found in liver homogenate during the 10--16th day after Walker tumor transplantation. Only the enzyme system esterifying cholesterol in the cytosol at pH 6.5 was stimulated while the activity of similar enzymes in mitochondria, microsomes and cytosol at an acid pH were not affected. Activity of the cytosol enzyme esterifying cholesterol at pH 6.5 was also enhanced during the active growth of Zajdela hepatoma and during the period of chemical carcinogenesis characterized by the appearance of first palpable subcutaneous tumors. Enhanced activity of cholesterol esterifying enzymes in the liver exactly coincided with periods of elevated levels of cholesteryl 14-methylhexadecanoate in the liver and blood plasma as described earlier. An increased demand of the tumor-bearing host for this cholesteryl ester utilized as a co-factor for enhanced protein synthesis is obviously met by its stimulated production in the liver tissue.

Animals↗
PubMed1978

Heparin-sepharose 4B at low temperatures retains ribosomes.

Ribosomes were separated by zonal ultracentrifugation from the fraction of reticulocyte postmitochondrial supernatants retained on heparin bound to Sepharose 4B at 4 degrees C. No ribosomes were retained at 22 degrees C. Ribosomes were also adsorbed on Sepharose 4B and 6B at low temperatures and could be eluted after increasing the column temperature.

Centrifugation, Density Gradient↗
PubMed1978

All factors required for protein synthesis are retained on heparin bound to Sepharose.

1. Postmitochondrial supernatants of rabbit reticulocyte lysates were chromatographed on heparin bound to Sepharose 4B, and the fraction retained on affinity columns was separated by subsequent gel filtration on Sepharose 4B into three fractions, two of them active in protein synthesis. 2. The heavier fraction sedimented at 40S and contained more than 10% RNA. This consisted predominantly of a 12S component, with smaller amounts of the 9S and 4S RNA species. The lighter fraction (18-20S) was composed of proteins with less than 1% RNA. 3. Different enzymic activities were associated with these fractions. 4. In the presence of both fractions, efficient translation took place on combined ribosomal subunits of rat liver with added cofactors. Globin messenger ribonucleoprotein stimulated this translation 5-6-fold. 5. Relatively large complexes of all factors required for protein synthesis are apparently isolated from reticulocytes by affinity chromatography on heparin-Sepharose 4B. Such complexes may occur naturally in the cytoplasm of mammalian cells.

Animals↗