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B Kemper

Publications and source records attributed to B Kemper.

At least 145 records · Page 8Linked to original sources
PubMed1976

Pre-proparathyroid hormone: analysis of radioactive tryptic peptides and amino acid sequence.

The amino acid sequence of bovine pre-proparathyroid hormone has been partially determined by analysis of the polypeptide labeled selectively with radioactive amino acids. Analysis of tryptic peptides containing methionine or lysine indicated that parathyroid hormone, proparathyroid hormone, and pre-proparathyroid hormone had several common peptides. Two lysine-containing peptides present in proparathyroid hormone but not in parathyroid hormone were also present in pre-proparathyroid hormone. In addition, pre-proparathyroid hormone contained several additional lysine- and methionine-containing peptides not present in parathyroid hormone or proparathyroid hormone. Analysis by repetitive Edman degradation of the polypeptide labeled with lysine, methionine, and other amino acids indicated that pre-proparathyroid hormone contained 25 additional amino acids at the amino terminus of proparathyroid hormone; the identities of 17 of the 25 amino acids have been established. An unusual feature found was the presence of methionyl-methionyl at the amino terminus and the presence of 5 methionines within the first 14 amino acids.

Amino Acid Sequence↗
PubMed1976

Pre-proparathyroid hormone: fidelity of the translation of parathyroid messenger RNA by extracts of wheat germ.

Pre-proparathyroid hormone is the major protein synthesized in wheat-germ extracts in response to addition of an 8-15S fraction of parathyroid RNA. The accuracy of the translation of the mRNA from parathyroid tissue was examined by analysis of the carboxyl-terminal tryptic peptide and the amino-terminal amino acid of the protein, by analysis of the size distribution of the mRNA, and by translation of the mRNA in a second cell-free extract. When 8-15S RNA was fractionated on a sucrose gradient containing formamide, RNA that supported the synthesis of pre-proparathyroid hormone was present in a single symmetrical peak, suggesting that it was homogeneous. Analyses by paper chromatography and electrophoresis of the proline-containing tryptic peptides of pre-proparathyroid hormone indicate that they are identical with the corresponding proline-containing peptides of parathyroid hormone. Because the COOH-terminal tryptic peptide of parathyroid hormone contains proline, the data indicate that the COOH termini of pre-proparathyroid hormone and parathyroid hormone are identical. Methionine from initiator [35S]Met-tRNAfMet was rapidly incorporated into pre-proparathyroid hormone by the wheat-germ extract, and a single-step Edman degradation selectively removed almost all of the initiator [35S]methionine present in pre-proparathyroid hormone. Translation of the 8-15S RNA in a cell-free extract from Krebs-II ascites cells resulted in a protein that comigrated with pre-proparathyroid hormone on sodium dodecyl sulfate-acrylamide gel electrophoresis. These data support the conclusion that the wheat-germ system accurately translates the mRNA for parathyroid hormone, and they strengthen the contention that pre-proparathyroid hormone is the initial biosynthetic product.

Animals↗
PubMed1976

Function of gene 49 of bacteriophage T4. II. Analysis of intracellular development and the structure of very fast-sedimenting DNA.

With the exception of mutants in gene 49, all mutants in phage T4 defective in the process of head filling accumulate a normal replicative DNA intermediate of 200S. Mutants in gene 49 produce a very fast-sedimenting (VFS) DNA with s values of greater than 1,000S. The intracellular development of the VFS-DNA generated in gene 49-defective phage-infected cells was followed by sedimentation analysis of crude lysates on neutral sucrose gradients. It was observed that the production of a 200S replicative intermediate is one step in the development of VFS-DNA. After restoring permissive conditions the development of the VFS-DNA can be reversed, but the 200S form is not regenerated under these conditions. The process of head filling can take place from the VFS-DNA under permissive conditions. From the absence of other components in the VFS-DNA complexes, its high resistance to shearing, its resistance against the attack of the single-strand-specific nuclease S1, and from its appearance in the electron microscope, a complex structure of tightly packed DNA is inferred. The demonstration by the electron microscope of branched DNA structures sometimes closely related to partially filled heads is taken in support of the idea that the process of head filling in gene 49-defective phage-infected cells is blocked by some steric hindrance in the DNA. In light of these results, the role of gene 49 is discussed as a control function for the clearance of these structures. A fixation procedure for cross-linking of gene 49-defective heads to the VFS-DNA allowed us to study progressive stages in the process of head filling. Electron microscopic evidence is presented which suggests that during the initial events the DNA accumulates in the vertexes of the head.

Cell Membrane↗
PubMed1976

Function of gene 49 of bacteriophage T4. I. Isolation and biochemical characterization of very fast-sedimenting DNA.

Very fast-sedimenting DNA was isolated from cells after infection with gene 49 defective phage T4. This DNA appeared membrane bound throughout the time after infection and could be isolated either in the membrane-bound form (M-DNA) or free of membrane (released DNA) depending on the lysis procedure. Released DNA formed complexes of marked stability with sedimentation velocities between 1,400S and 2,100S. These complexes did not seem to contain material other than DNA. This was concluded from the results of RNA, protein, and membrane labeling experiments and density analysis. In addition, these complexes were resistant against treatment with n-butanol, phenol. chloroform-methanol, sodium dodecyl sulfate, Sarkosyl, Pronase, RNase, or lysozyme. The observation that more then 90% of the purified very fast-sedimenting DNA is retrapped by magnesium-Sarkosyl crystals (M-band) suggests that the M-band technique may not be sufficient as a test for DNA-membrane attachment.

Cell Membrane↗
PubMed1975

Pre - proparathyroid hormone identified by cell - free translation of messenger RNA from hyperplastic human parathyroid tissue.

An 8-15S fraction of RNA isolated from hyperplastic human parathyroid tissue (primary chief-cell hyperplasia) and translated in a cell-free extract of wheat germ directs the synthesis of a protein that shares antigenic determinants and tryptic peptides with parathyroid hormone and its previously recognized immediated precursor, proparathyroid hormone. In addition, the protein contains tryptic peptides not found in proparathyroid hormone and migrates more slowly than does proparathyroid hormone on both urea-acid and urea-sodium dodecyl sulfate polyacrylamide gels, indicating that it is more acidic and larger than proparathyroid hormone. Sequential Edman degradation of the cell-free protein, radiolabeled with [35S]methionine, for 25 cycles released [35S]methionine at cycles 1, 7, 11, and 14, indicating that the NH2-terminal peptide sequence of the protein differs from that of both proparathyroid hormone and parathyroid hormone. We propose that this protein is an early biosynthetic precursor of human parathyroid hormone, pre-proparathyroid hormone, analogous to that identified recently by in vitro translation of bovine parathyroid mRNA.

Cell-Free System↗
PubMed1975

Microtubules and the intracellular conversion of proparathyroid hormone to parathyroid hormone.

The effects of several compounds which interfere with cellular microfilaments and microtubules on the conversion of proparathyroid hormone (ProPTH) to parathyroid hormone (PTH) were examined in slices of bovine parathyroid slices incubated in vitro with 3H-leucine. Inhibitors of microtubular function, vinblastine and colchicine, increased the ratio of 3H-labeled ProPTH to PTH in the tissue by 2- to 3-fold. Cytochalasin B, an inhibitor of microfilaments, was without effect. Concentrations of colchicine as low as 10-6M maximally increased the ratio of ProPTH to PTH, whereas lumicolchicine, an analogue of colchicine which does not affect the function of microtubules, had no effect at concentrations as high as 10-4M. The increased ratio of ProPTH to PTH was due partly to a stimulation by vinblastine and colchicine of the incorporation of 3H-leucine into ProPTH but not into general protein. However, after short incubations of parathyroid tissue with 3-H-leucine, the amount of 3H-labeled PTH was less in colchine-treated incubations than in control incubations. In the presence of vinblastine, after a 20-min incubation of parathyroid slices with 3H-leucine and vinblastine, ProPTH was not completely converted to PTH by an additional 90-min "chase" incubation with unlabeled leucine while a 20-min "chase" incubations is sufficient to convert essentially all the ProPTH to PTH in control incubations. These data suggest that the increased ratio of ProPTH to PTH is also due to a partial inhibition of the conversion ProPTH to PTH by vinblastine and colchicine. The data are consistent with the hypothesis that microtubules facilitate the transport of newly synthesized ProPTH to its intracellular site of cleavage to PTH.

Animals↗
PubMed1975

Calcium-dependent intracellular degradation of parathyroid hormone: a possible mechanism for the regulation of hormone stores.

The dynamics of parathyroid hormone (PTH) biosynthesis, storage, and secretion in bovine parathyroid slices in vitro in response to alterations in the concentrations of extracellular calcium were studied. Hormone biosynthesis was evaluated by using polyacrylamide gel electrophoresis to measure incorporation of [3H]leucine into newly synthesized PTH and proparathyroid hormone (ProPTH) during short (35 min) incubations. Amounts of newly synthesized PTH stored in and secreted from the tissue slices were determined by electrophoretic analysis of [3H]PTH in extracts of tissue and media. Total PTH and ProPTH is slices and media were measured by specific radioimmunoassays. PTH secretion rates changes 5-fold when calcium was lowered from 2mM to 1mM. Secretion of some PTH continued despite high concentrations of calcium (5 mM). Biosynthesis of ProPTH was changed only slightly, and conversion of ProPTH to PTH was independent of the extracellular calcium concentration. Tissue stores of PTH increased during incubation of parathyroid slices in medium containing high amounts of calcium. The increase in stores was much less, however, than predicted by the findings of marked suppression of secretion and little change in rates of PTH biosynthesis. In high concentrations of calcium, a large fraction (up to 50%) of newly synthesized PTH was degraded within the tissue, whereas in low concentrations of calcium, little (less than 10%) of the PTH was degraded. No fragments of PTH or ProPTH were identified in either extracts of tissue or media, suggesting that degradation occurred rapidly by general proteolysis rather than by limited, specific endopeptidase activity. The data suggest that the parathyroid cell contains a calcium-sensitive degradative pathway for PTH and that this pathway may be involved in the regulation of hormone production and secretion.

Animals↗
PubMed1975

Adam Politzer, otology and the Centennial Exhibition of 1876.

The Centennial Exhibition of 1876 was held in Philadelphia. Among the exhibits was a collection of temporal bone dissections produced by Adam Politzer of Vienna. This exhibit included both normal and pathological temporal bones, and emphasized the relationship of the tympanic membrane to the middle ear, external canal and bony labyrinth. At the close of the Centennial Exhibition the collection was purchased by the College of Physicians of Philadelphia. This collection and the congress associated with the Centennial had a tangible effect on the otology in this country.

Ear Canal↗
PubMed1974

Parathyroid secretion: discovery of a major calcium-dependent protein.

Bovine parathyroid tissue incubated in vitro secretes a protein that is distinct from both parathyroid hormone and proparathyroid hormone and comprises about 50 percent of the total secreted protein. This protein appears to be an aggregate consisting of two or more subunits of molecular weight 70,000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Although the function of this protein is unknown, the secretion rates of both the protein and parathyroid hormone respond in parallel to changes in the concentration of calcium in the medium.

Amino Acids↗
PubMed1974

Pre-proparathyroid hormone: a direct translation product of parathyroid messenger RNA.

An 8-15S RNA fraction from calf parathyroid glands stimulated the incorporation of radioactive lysine and methionine into protein by 15- to 30-fold in a wheat germ extract. The major product, representing 25% of the total protein synthesized, could be bound to an antiserum to parathyroid hormone and binding was inhibited by parathyroid hormone. The chromatographic mobilities of the two tryptic peptides of the cell-free product that contained methionine were identical to the corresponding peptides of parathyroid hormone. Upon electrophoresis in acidic or sodium dodecyl sulfate-acrylamide gels, the cell-free product migrated more slowly than either parathyroid hormone or its biosynthetic precursor, proparathyroid hormone. Analysis of cyanogen bromide products indicated that the cell-free product contained an additional sequence of amino acids at the amino-terminal end. A protein corresponding to the cell-free product could not be detected in intact cells even during incubations with [(3)H]leucine as short as 2 min, which suggests the protein may be a transient precursor to proparathyroid hormone.

Amino Acid Sequence↗