Function of the delipidated beta-adrenergic receptor appears to require a fatty acid or a neutral lipid in addition to phospholipids

Detergent-solubilized preparations of the beta-adrenergic receptor (R) and of the guanyl nucleotide binding proteins (Gs) were extensively treated to remove phospholipids and cholesterol. Reconstitution of an R-Gs system was subsequently performed in the presence of a mixture of natural phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine or the synthetic dioleoyl derivatives of the same phospholipids. In both cases, an additional lipid was required for the agonist-dependent activation of Gs. The requirement could be fulfilled by alpha-tocopherol, or by unsaturated fatty acids such as oleic acid. Inclusion of this non-phosphorylated lipid in the reconstituted system enhanced the isoproterenol-dependent activation of Gs by guanosine 5'-O-[gamma-thio]triphosphate 16-33-fold. The rate of activation was largely dependent on the addition of the agonist. Efficient functional reconstitution of R-Gs was thus achieved in a totally defined lipid system. Additional studies of the reconstituted system and of the native membrane led to the notion that the non-phosphorylated lipid plays a role in the function of the hormone-R complex.     

Effect of the phase state of lipids on their interaction with cobra cytotoxin

Interaction between cytotoxin of the Central Asia cobra venom and dimiristoylphosphatidylcholine bilayer depending on its phase state was studied by ESR with spin label. A conclusion can be drawn that the efficiency of cytotoxin effect on the membranes depends on their phase state. Cytotoxin molecules are incorporated into myophile region of the bilayer, only if the latter is in the liquid crystal state. The interaction between cytotoxins and lipids of the bilayer in a gel state is in the main conditioned by electrostatic forces.     

3-Hydroxyanthranilic acid metabolism. IV. Spectrophotometric evidence for the formation of an intermediate

Evidence has been presented for the formation of an intermediate compound in the metabolism of 3-hydroxyanthranilic acid to quinolinic acid by 3-hydroxyanthranilase from rat liver preparations. The production of the intermediate was demonstrated by spectrophotometric analyses and quinolinic acid measurements of incubation mixtures in which small amounts of acetone powder extracts of rat liver were used as the enzyme source. The calculated extinction coefficient of the compound was more than double that of the substrate or of the final product, quinolinic acid.The intermediate was shown to be an oxidation product of 3-hydroxyanthranilate as indicated by Thunberg experiments. The data obtained indicate that the intermediate may be a quinone-type compound.     

Über die Ursachen der Osmotoleranz bei Hefen

Zusammenfassung Mit Untersuchungen über die Abhängigkeit des Zellvolumens vom osmotischen Wert und über die Konzentration der Zellinhaltsstoffe wird versucht, zur Kenntnis der Ursachen der Osmotoleranz bei Hefen beizutragen. In konzentrierten Lösungen verringern alle untersuchten Hefen ihr Volumen, die osmotoleranten Hefen aber weniger als die nichtosmotoleranten. Der Beginn einer meßbaren Volumenverringerung tritt bei osmotoleranten Hefen bei höheren Konzentrationen ein als bei nichtosmotoleranten. Eine Abhängigkeit der Zellgröße vom osmotischen Wert kann nur in einem bestimmten Konzentrationsbereich (zwischen 0,7–2% und 10% NaCl) festgestellt werden. Darunter fehlt eine osmotische Reaktion, und darüber bleibt die Zellgröße gleich. In Nährlösungen mit erhöhtem osmotischen Wert vermehren sich Zellen beider Typen in ihrer normalen Größe. Der osmotische Wert ihres Zellinhaltes ist annähernd gleich groß. Eine veränderte Struktur des Zellplasmas bzw. ein dadurch bedingter höherer Gehalt an fest gebundenem Hydratationswasser wird als Ursache der Osmotoleranz bei Hefen angesehen.

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About the causes of osmotolerance in yeasts

Summary The question, if the yeast cell volume depends on the osmotic pressure and on the solutes of the cell, has been investigated. In concentrated solutions all yeasts investigated reduced their volume. A smaller reduction was found in osmotolerant yeasts. Osmotolerant yeasts begin to reduce their volume at higher osmotic pressures than non-osmotolerant ones. In concentrated nutrient media the cells of osmotolerant and non-osmotolerant yeasts grow in their normal size. The cell size depends only in the range between 0.7 to 2% and 10% NaCl approximately on the osmotic pressure of the surrounding medium. Beneath 2% there is no osmotic reaction and above 10% the cell size remains unchanged. The osmotic value in the cells of both yeast types is about the same. Causes of osmotolerance in yeasts may be a modified structure of cytoplasm and an increased content of bound water.

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(Prof. Dr. S. Windisch)