Sulfate influx across the rabbit ileal brush border membrane: Sodium and proton dependence,and substrate specificities

Summary In intact ileal mucosa, uptake of SO₄ across the brush border membrane requires the presence of Na and is saturable, withK1/2=1.3mm at 140mm Na (P.L. Smith, S.A. Orellana & M. Field, 1981.J. Membrane Biol. 63:199–206). The present study examines the substrate specificities and transport stoichiometry of the Na-dependent SO₄ uptake process. The effects of variations in medium anion and cation composition on lumen-to-epithelium influx of SO₄ (J _me ^SO4 ) were determined under short-circuit conditions.J _me ^SO4 is inhibited by thiosulfate, but not by phosphate, methylsulfate, vanadate or taurocholate. Cl is weakly inhibitory. Uptake of SO₄ is poorly supported by Li, and is unaffected by K, indicating a specific dependence on Na. At low SO₄ concentration (0.22mm),J _me ^SO4 is a hyperbolic function of medium Na concentration; the corresponding Hill plot is linear with a slope of 1.0, suggesting a transport stoichiometry of 1 Na: 1 SO₄. At high SO₄ concentration (6.7mm), the Na-dependent SO₄ velocity curve is sigmoidal and yields a Hill plot which is again linear but has a slope of 1.56, suggesting transport of more than 1 Na per SO₄. SO₄ uptake in presence of Na exhibits a dependence on medium pH. At 0.22mm SO₄ and 140mm Na,J _me ^SO4 was doubled by lowering pH from 7.4 to 6.8. However, at 6.7mm SO₄ and 140mm Na, changing pH had no effect onJ _me ^SO4 over the range 6.8 to 8.5. The pH dependence ofJ _me ^SO4 at 6.7mm SO₄ was restored when medium Na was lowered to 3mm, suggesting that pH sensitivity is a function of the concentration of preformed NaSO ₄ ^– ion pair. The results suggest that SO₄ influx across the ileal brush border occurs by electroneutral Na⁺/NaSO ₄ ^– or Na⁺/H⁺/SO ₄ ^2– cotransport, the former being favored by high concentrations of Na and SO₄.     

Thiolated nucleotides in yeast transfer RNA

By culturing Saccharomyces cerevisiae in growth medium containing Mg³⁵SO₄, we have determined the extent and variation of tRNA thiolation in this yeast. We find that 5-methoxycarbonylmethyl-2-thiouridine (mcm⁵s²U)¹ is the major, if not only, thiolated derivative in S. cerevisiae tRNA. In addition, a comparison of the chromatographic mobility of mcm⁵s²Up on cellulose thin layers with those reported for unknown uridine derivatives found in purified yeast tRNA digests, leads to the conclusion that at least two of these tRNAs contain this modification.     

Computer-aided Diagnosis of Acute Abdominal Pain

This paper reports a controlled prospective unselected real-time comparison of human and computer-aided diagnosis in a series of 304 patients suffering from abdominal pain of acute onset.The computing system''s overall diagnostic accuracy (91·8%) was significantly higher than that of the most senior member of the clinical team to see each case (79·6%). It is suggested as a result of these studies that the provision of such a system to aid the clinician is both feasible in a real-time clinical setting, and likely to be of practical value, albeit in a small percentage of cases.     

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.     

Further observations on the effect of ethionine on the synthesis of β-galactosidase inEscherichia coli: Formation of an immunologically cross-reacting protein

It was found that ethionine partially inhibits the transport of the inducer (TMG) of β-galactosidase into the cells ofEscherichia coli ML-30. The synthesis of β-galactosidase-specific messenger RNA is not inhibited. Ethionine appears to be incorporated into proteins synthesized by the strains used. The incorporation of ethionine into the molecule of β-galactosidase results in the synthesis of an enzymically inactive, immunologically cross-reacting protein.     

Ultraviolet Inactivation and Photoproducts of Transforming DNA Irradiated at Low Temperatures

Solutions of Haemophilus influenzae transforming DNA were irradiated at temperatures ranging from 25°C to - 196°C. Temperature dependence of the formation of thymine-containing dimers was closely correlated with inactivation of transforming activity; in general, both dimerization and inactivation decreased with decreasing temperature. The fraction of nonphotoreactivable damage increased with increasing dose at low temperatures. The nonphotoreactivable spore-type photoproduct was formed at low temperatures with a maximum at - 100°C, a temperature at which the nonphotoreactivable biological inactivation was also a maximum. Intrastrand cross-linking, like dimer formation, decreased with decreasing irradiation temperature.     

The conversion of injected glucose into renal glycogen and mucopolysaccharides

Summary Tritiated glucose has been injected into rabbits in various states of hydration. The renal papilla of all animals showed an uptake of the label, converted into glycogen, and into mucopolysaccharides, in a manner dependent on the water balance of the animal.In papillae of control animals, the glycogen of the collecting duct epithelial cells and the mucopolysaccharides of the interstitium were labelled.In papillae of animals in an aqueous diuresis, the collecting duct glycogen was lightly labelled and there was no label over the interstitium.Antidiuretic hormone caused a diversion of label from the collecting ducts into interstitial mucopolysaccharides.The significance of these findings, with respect to renal concentrating ability, is discussed.The author wishes to thank Dr. M. K. S. Hathorn for help with the statistical analysis. Mr. K. Gamblin and Mr. P. L. Hyam gave valuable technical assistance. This research formed a part of the work approved for the degree of Ph. D. (London).