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Biomedical subjects

S Prehn

Publications and source records attributed to S Prehn.

At least 55 records · Page 3Linked to original sources
PubMed1985

Maturation of rabbit reticulocytes: susceptibility of mitochondria to ATP-dependent proteolysis is determined by the maturational state of reticulocyte.

A simple procedure is described to separate reticulocytes of different maturity in high yield. It is shown that exhaustion of supply of mitochondria susceptible to degradation by the lipoxygenase-ATP-dependent proteolysis system limits the extent of breakdown of mitochondria during in vitro maturation. The susceptibility of mitochondria depends on the maturity of the reticulocytes. Incubation in the presence of calcium ions and calcium ionophore leads to full susceptibility of mitochondria in immature reticulocytes but has no effect on those in mature reticulocytes which are already fully susceptible to degradation. Conditions which lead to rapid degradation of mitochondria do not affect the behaviour of the reticulocyte count. There appears to be no obligatory connection between the breakdown of mitochondria and of ribosomes.

Adenosine Triphosphate↗
PubMed1985

Proteolysis during in vitro-maturation of rabbit reticulocytes.

We investigated the ATP-dependent proteolysis, cytochrome oxidase and the succinate-cytochrome c-oxidoreductase in reticulocytes under different conditions of incubation in vitro at 37 degrees C. Under standard conditions the proteolysis virtually stops after 4 h. The degradation of the stroma proteins amounted to 30-65% depending on the percentage of reticulocytes. The decrease of the cytochrome oxidase amounted to 70% after 20 h of incubation. Inhibition of the cytosolic reticulocyte lipoxygenase (LOX) by the reversible inhibitor salicylhydroxamate (SHAM) leads to an inhibition of both proteolysis and cytochrome oxidase activity by about two-thirds after 20 h of incubation. In the presence of a Ca++-ionophore the rate of proteolysis was increased by 33%, while the cytochrome oxidase and succinate-cytochrome c-oxidoreductase activities both decreased more rapidly than in the control experiments.

Adenosine Triphosphate↗
PubMed1983

In vitro maturation of rabbit reticulocytes. III. Response of lipoxygenase.

Lipoxygenase activity with linoleic acid as substrate and the immunologically detectable amount of lipoxygenase protein were estimated in the course of in vitro maturation of rabbit reticulocytes withdrawn at the sixth day of an experimental bleeding anaemia. With unseparated cell mixture there was a significant increase in the lipoxygenase activity of 67 +/- 15% after a maturation period of 4 h followed by a decrease up to the initial level. The maturational changes were more pronounced when the fraction of youngest reticulocytes after buoyant density separation in a serum albumin gradient was used, whereas the cells of medium density failed to show the intermittent increase. The lipoxygenase activity was largely paralleled by the amount of lipoxygenase protein. The increase of lipoxygenase was prevented by either anaerobiosis or addition of oligomycin. The protein synthesis was greatly decreased after 4 h of incubation. The decline of the amount of lipoxygenase between 4 and 24 h incubation is probably largely caused by proteolysis. The results support former interpretations as to the synthesis and biological dynamics of lipoxygenase in reticulocytes.

Animals↗
PubMed1982

Carp insulin: amino acid sequence, biological activity and structural properties.

The amino acid sequence of insulin of carp (Cyprinus carpio) has been determined and correlated with its biological activity in a fat-cell test and its structural properties as measured by circular dichroism and sedimentation analysis. The amino acid sequence of carp insulin displays some unusual features: the B chain is longer at the N terminus by two residues as compared with mammalian insulins and there are substitutions of the charged residues, found in most insulins at positions B21 and B22, by proline and threonine respectively. On the other hand, all amino acid residues essential for biological activity and for the association of insulin monomers are the same in carp insulin. Accordingly, the half-maximal response in a fat-cell test is reached with carp insulin at concentrations which are only three times higher than with porcine insulin and the maximal response is the same. The circular dichroism spectrum of carp insulin resembles greatly that of bovine insulin indicating that it has a similar spatial structure. Despite amino acid substitutions in the dimer-dimer contact region, carp insulin is able to form hexamers.

Adipose Tissue↗
PubMed1982

Different modes of membrane interactions of the signal sequence of carp preproinsulin and of the insertion sequence of rabbit cytochrome b5.

The signal segment of the secretory protein carp preproinsulin is shown to be bound by a protein receptor present in the rough endoplasmic reticulum membrane. The receptor does not bind the insertion segment of the integral membrane protein cytochrome b5. On the other hand, the insertion sequence, in contrast to the signal sequence, is dissolved into the lipid bilayer of natural and artificial membranes. Hydrophobicity or length per se of the two types of peptides cannot be responsible for their different behaviour. We rather propose that the difference resides in their tertiary structure. Insertion peptides may form a compact structure with a diffuse hydrophobic surface, presumably by internal hydrogen bonding. Signal peptides would form hydrogen bonds with a membrane-bound receptor protein, presumably by producing a beta-sheet structure, but their extended structure in aqueous solution would not allow them to dissolve into lipid bilayers.

Amino Acid Sequence↗
PubMed1980

Cloning of carp preproinsulin cDNA in the bacterial plasmid pBR322.

The successful cloning of recombinants between cDNA from fractionated poly(A)+-RNA of Brockmann bodies of the carp and the plasmid pBR322 in Escherichia coli chi 1776 is reported. One of the recombinant clones has been identified as a preproinsulin-cDNA recombinant by the hybrid-arrest translation assay. Recombination was at the PstI site of pBR322; reconstitution of this site was by 3'-tailing of the vector with dGn. The transformants were screened by in situ hybridization with kinase-labeled poly(A)+-RNA sedimenting at 9S from Brockmann bodies. Restriction analysis was performed on 26 of the strongly hybridizing clones to estimate the size of the inserted cDNA. Six of the recombinants studied contain inserts of a size approximating to full length 9S preproinsulin mRNA. The hybrid-arrest translation assay on selected clones identified one as a recombinant containing the preproinsulin cDNA sequence.

Animals↗
PubMed1980

Demonstration of specific receptors of the rough endoplasmic membrane for the signal sequence of carp preproinsulin.

1. Evidence is given for the cotranslational processing in a wheat germ cell-free system of carp preproinsulin to proinsulin by dog pancreatic rough endoplasmic membranes stripped of ribosomes by EDTA. Concomitantly with processing there is a translocation of the protein across the membrane as shown by the accessibility to proteases. Conversion of preproinsulin to proinsulin occurs post-translationally only in the presence of detergent. 2. Stripped rough endoplasmic membranes bind a significant proportion of the cell-free translation products synthesized in a wheat germ system in response to poly(A)-rich RNA from carp islets. Among the bound material there is completed preproinsulin. The bound material is accessible to proteases. It is located on the cytoplasmic side of the membranes. Peptides lacking a signal sequence, such as globin or proinsulin, are not bound. The binding can be abolished by pretreatment of the rough membranes with proteases. Neither smooth endoplasmic membranes from dog pancreas nor erythrocyte plasma membranes from rabbits are able to bind signal peptides. The binding sites on the rough membranes can be saturated with cell-free products coded by carpislet RNA and are then no longer able to process preproinsulin to proinsulin in a contranslational assay. The amount of membranes necessary to bind a certain amount of cell-free products post-translationally corresponds roughly to the amount required for complete conversion of preproinsulin to proinsulin cotranslationally. The binding phenomenon occurs independently of the presence of ribosomes and is not sensitive to high ionic strength. A hydrophobic peptide (Ac-Lys-Phe-Phe-Gly-Leu-Nle-NH2) did not compete with signal peptides. 3. The results show that stripped rough endoplasmic membranes possess specific protein-containing receptors for signal sequences on their cytoplasmic side. The recognition of the signal by the endoplasmic membranes occurs without participation of the ribosomes. The latter are only required for the translocation of the nascent peptide into the lumen of the membrane.

Animals↗
PubMed1980

[In vitro maturation of reticulocytes. Behavior of RNA and inorganic pyrophosphatase].

A simple system of incubation of reticulocytes with a small degree of haemolysis has been developed. It was possible to test the influence of inorganic phosphate, pH-values in the range of 7.0--9.0 and anaerobic conditions on the in vitro maturation of reticulocytes. As main criteria of the maturation the RNA-content and the activity of PPase has been tested. The decrease of the RNA-content and the activity of the PPase is highly significant during maturation. The decrease of RNA and the reduction of reticulocytes are stimulated by inorganic phosphate.

Anaerobiosis↗
PubMed1978

Synthesis of carp proinsulin in Xenopus oocytes.

Total poly(A)-containing RNA from Brockmann boides of carp (Cyprinus carpio) directs the synthesis of authentic carp proinsulin in Xenopus oocytes. Neither preproinsulin nor further processing of the proinsulin to insulin can be detected in the oocytes.

Animals↗
PubMed1978

Preparation and characterization of insulin of carp (Cyprinus carpio).

Insulin of carp (Cyprinus carpio) was isolated and crystallized. The insulin was biologically active in two tests; it decreased the blood glucose level and stimulated 14CO2-formation from glucose. The chemical properties are similar to those of insulins from other species. The insulins of carp and of mammals differ greatly immunologically. Antibodies against carp insulin crossreact with carp proinsulin.

Amino Acids↗
PubMed1975

[Problem in the partial separation of X- and Y-carrying human spermatozoa].

The introduction of a fluorescent staining technique for identification of Y chromosome made possible the distinction of X- and Y-bearing human spermatozoa. Using this fluorescence analysis the isolation of Y- and X-bearing human spermatozoa were investigated employing two different methods for separation of spermatozoa. 1. The migration of human spermatozoa in cervical mucus obtained from women shortly before mid-cycle was studied, using an in-vitro method for horizontal sperm penetration. Basing on the progressive sperm motility in cervical mucus, a fraction rich in Y-bearing spermatozoa in the frontal zone of sperm migration was found. 2. Gradient centrifugation at different rotor speeds using a discontinous sucrose gradient has been employed for separation of human spermatozoa. A significant trend for separation of Y- and X-bearing spermatozoa was demonstrated. The results were shortly discussed.

Centrifugation, Density Gradient↗