Thermodynamic aspects of plant cell adhesion to polymer surfaces

Summary A thermodynamic model of particle adhesion from a suspension onto a solid surface is used to predict the extent of adhesion of suspension-cultured Catharanthus roseus cells to the following polymer substrates: fluorinated ethylene-propylene (FEP), polystyrene (PS), polyethylene terephthalate (PET), sulphonated polystyrene (SPS), and glass. According to this model, the extent of adhesion is determined by the surface tensions of the plant cells, the polymer substrates, and the suspending liquid medium. Experimentally, adhesion of the washed plant cells was found to decrease with increasing substrate surface tension, following the sequence FEP>PS>PET>SPS>glass, when the surface tension of the liquid was greater than that of the plant cells, in agreement with the model. However, adhesion increased with increasing substrate surface tension when the liquid surface tension was lower than the cellular surface tension, also in agreement with the model. When the liquid and cellular tensions were equal the extent of adhesion was independent of the substrate surface tension. This also agrees with model predictions and leads to a value for the surface tension of C. roseus cells of approximately 54 ergs/cm² which is in agreement with a value obtained from contact angle measurements on layers of cells and sedimentation volume analysis. The cellular surface tension determined by the sedimentation volume method showed a biphasic alteration during growth cycles of C. roseus cell cultures. These variations (between 55 and 58 ergs/cm²) agree with the pattern of adhesion previously described.     

Enzymic properties of intestinal aminopeptidase P: a new continuous assay

A continuous photometric assay of aminopeptidase P activity was developed which is based on a coupled enzymic assay with the substrate Gly-Pro-Pro-pNA and DPP IV as auxiliary enzyme. This assay was used to evaluate the kinetic parameters and inhibitory profile of intestinal brush border aminopeptidase P.     

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Ohne Zusammenfassung     

Localization of a highly immunogenic region on the acetylcholine receptor alpha-subunit

Antibodies to synthetic peptides were employed in order to map domains on the alpha-subunit of the acetylcholine receptor to which several monoclonal antibodies are directed. Five peptides corresponding to residues 1-20, 126-143, 169-181, 330-340 and 351-368 of the receptor alpha-subunit were synthesized and antibodies against them were elicited. The anti-peptide antibodies were employed along with the monoclonal antibodies to identify fragments of S. aureus V8 protease digested- alpha-subunit in immunoblotting experiments. Our results demonstrate that a highly immunogenic region of the alpha-subunit is located on a carboxy-terminal 14 kDa portion of the alpha-subunit. This region also seems to undergo antigenic changes during muscle development. A monoclonal antibody directed against the cholinergic binding site of the acetylcholine receptor reacted with an 18 kDa segment of the alpha-subunit which bound alpha-bungarotoxin as well as antibodies directed against peptide 169-181.     

A defect in mobilization of cholesteryl esters in rabbit macrophages

Macrophages provide an important way for cholesteryl esters to accumulate in tissues in pathologic amounts. We studied cholesteryl ester metabolism in thioglycollate-induced peritoneal macrophages obtained from normocholesterolemic and hypercholesterolemic rabbits. The macrophage preparations from normocholesterolemic rabbit (MN cells) had 26 nmol esterified cholesterol/mg cellular protein, incorporated 1 nmol of labeled oleate into cholesteryloleate/2 h per mg cellular protein and had an acyl-coenzyme A:cholesterol acyltransferase activity of 22 pmol cholesterylpalmitate formed/min per mg protein in isolated membranes. The macrophage preparations from hypercholesterolemic rabbits (MHC cells) contained a 12-fold greater mass of cholesteryl ester, had an 8-times higher rate of formation of cholesteryloleate, and had 3-times more acyl-coenzyme A:cholesterol acyltransferase activity in the isolated membranes. When a cholesterol acceptor (10% fetal bovine serum or 10 mg of lipid-free fetal bovine serum protein) was added to the culture medium of rabbit MHC cells, the MHC cells retained more than 70% of their cholesteryl esters after 48 h of incubation. In contrast, when a cholesterol acceptor (10% fetal bovine serum) was added to the medium of thioglycollate-induced, cholesterol-enriched macrophages from mice, the mice macrophages retained only 19% of their cholesteryl esters after 48 h of incubation. The limited capacity of rabbit macrophages to release unesterified cholesterol from stored cytoplasmic cholesteryl esters to an exogenous acceptor may be related to the propensity of rabbits to develop atherosclerotic lesions.     

NMR, CD and IR spectroscopies of a tridecanucleotide containing a no-base residue: coexistence of B and Z conformations.

The synthesis of the tridecadeoxynucleotide d(CGm5CGCGxACATGT), where x is the 1-cyano-2-deoxy-beta-D-erythropentofuranose, is described. The NMR, IR, CD studies at various salt concentrations and temperatures of this oligomer show that the B and Z conformations are simultaneously present in the same short DNA fragment. A single apurinic residue is sufficient for the coexistence of the B and Z helices on this oligomer.     

Eine nicht-reziproke Kreuzungssterilität zwischen ökologischen Rassen der Mücke Clunio marinus

Zusammenfassung Die in der Gezeitenzone lebende Mücke Clunio marinus ist längs der europäischen Küstenlinie verbreitet. Die experimentell geprüften Stämme verschiedener geographischer Herkunft repräsentieren ökologische Rassen, die sich in der zeitlichen Programmierung ihrer Entwicklung unterscheiden. Es wurde die Kreuzbarkeit zwischen insgesamt 7 Stämmen geprüft.Zwischen einzelnen Stämmen wurde eine nicht-reziproke Kreuzungssterilität (abgekürzt n.r.St.) nachgewiesen, bei der jeweils in einer Kreuzungsrichtung fertile Nachkommen entstanden und in der reziproken Kreuzung Nachkommen fehlten.Die Vererbung der n.r.St. wurde zwischen 2 Stämmen benachbarter Rassen mit der Methode der wiederholten Rückkreuzung geprüft. Es ergab sich ein matrokliner Erbgang. Die Befunde werden mit entsprechenden Ergebnissen von Laven an Culex pipiens verglichen.Die populationsgenetischen Konsequenzen der n.r.St. werden in Hinblick auf die Elimination von Kreuzungstypen, Genfluß und reproduktive Isolation betrachtet. Für die Bedeutung der n.r.St. im Freiland werden 3 Hypothesen erörtert: 1. Begleiterscheinung der genetisch divergierenden Rassen, 2. in einer Richtung wirksamer Isolationsmechanismus zwischen benachbarten Rassen und 3. Speciation.

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Summary The intertidal midge Clunio marinus is distributed along the European coast-line. Stocks from distinct locations differ in the programming of their emergence time. They represent ecological races. The crossability between 7 stocks was examined.Between some stocks a non-reciprocal cross sterility has been found, characterized by fertile hybrids in one cross direction, and no offspring in the reciprocal crosses.The cross Jean xSan was fertile, while the cross San xJean was sterile. After three backcrosses of the hybrid females to San males, the sterility in the reciprocal crosses with San females had not been changed. The maternal inheritance of this non-reciprocal sterility is compared with similar studies in Culex pipiens by Laven.According to aspects of population genetics, the non-reciprocal cross sterility is considered in view of elimination of crossing types, of gene flow and reproductive isolation. With regard to the significance of the non-reciprocal cross sterility in the field, three hypotheses are discussed: 1. by-product of evolutionary divergence in ecological races, 2. unilateral reproductive isolation which blocks the gene flow between adjacent populations only in one direction, and 3. speciation.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

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Herrn Professor Dr. Gerhard Krause zu seinem 65. Geburtstag.     

Metastable secondary structures in ribosomal RNA: a new method for analyzing the titration behavior of rRNA

The pH titration behavior of E. coli rRNA in the acid range has been analyzed by combining spectrophotometric and potentiometric titration data. The “simplest” model for the system, which considers as possible reactions the protonation of adenine (A), cytosine (C), and guanine (G) residues along with the opening of A·U and G·C base pairs, does not adequately account for the titration properties. It is postulated that extra reactions may occur in addition to those in the “simplest” model, and a new analytical method was developed to deal with this situation. Our approach yields the ultraviolet spectral changes which accompany the extra reactions, from which the nature of these reactions can in principle be deduced. The calculations also give, at each pH, the extents of the extra reactions as well as the extents of those reactions which comprise the “simplest” model. We infer that in acidic RNA solutions of 0.1M ionic strength there occur at least two extra reactions, each of which involves G residues. We propose that in the pH range 6.0 ≥ pH ≥ 3.8 triple-stranded helical sequences, presumably protonated G·C·G, are formed. These regions are replaced at lower pH by acid-stable structures involving G·G and A·A base pairs. In solutions of lower ionic strength (I = 0.01M) no triple strands are formed, but G·G and A·A regions seem to develop even at pH values as high as 6.0. At I = 0.1M, an acid–base titration cycle between pH 7 and 2.8 is not reversible; rRNA shows true hysteresis behavior. We conclude that in ribosomal RNA's, which are generally G-rich, guanine residues may participate in hitherto unpredicted conformations, some of which may be metastable while others are equilibrium structures.