No abstract

In the slime mold Dictyostelium discoideum polysioprenylphosphomannosides are substrates for membrane bound mannosyltransferases; the isolated and purified isoprenyl derivatives transfer mannose to protein in vitro in presence of membrane fractions. The biosynthesis of the mannolipids as well as the biosynthesis of a glucose containing cerebroside, which becomes synthesized in an early stage of the cell development proceeds under control of the cell differentiation. The isolation procedure and the properties of the glycolipids are described, and their functions for the cellular development are discussed.

Crude membrane fractions of Dictyostelium discoideum show the capacity to synthesize (1--3H)dolicholphosphate from (1--3H)dolichol. Formation of dolicholphosphate increased continuously over the first 15 min. The reaction rate was nearly linear with respect to the dolichol content up to 150 microM. The phosphate donor for the reaction is CTP. The optimum concentration of CTP is about 0,75 mM. The reaction is dependent on divalent metal ions, magnesium being more effective than calcium or manganese. The activity of the polyisoprenol kinase depends on the course of the early development. Maximum enzyme activities are present 4--6 h after the induction of the differentiation.

Mannosyltransferases in plasma membranes of Dictyostelium discoideum synthesize polyisoprenylphosphomannosides from exogenous polyisoprenylphosphates and GDP-mannose. The specificity of the enzymes depends on the chain length and the saturation of the polyisoprenols. Maximum activity is reached by a alpha-saturated C-55 polyisoprenylphosphate.

Struktur, spektrale Eigenschaften und Reaktivitat der am Redox-System des Thia-alloxazins 2 beteiligten Stufen RED, SEM und OX werden beschrieben. Ein-Elektronen-Oxidation von 2 fiihrt zu den Radikalen 4 und 5, deren weitere Oxidation bzw. Disproportionierung die Thiazoniumkationen 6 liefert. 6 ist nur in konz. Mineralsauren bestandig, in Anwesenheit Nucleophiler findet Addition an S(5) bzw. C(4a) statt. Hydrolyse von 6 ergibt in Abhangigkeit vom pH die Pseudobase 8a bzw. die Sulfoxide 7, die auch direkt durch HzOz-Oxidation erhalten werden konnen. Mit Alkoholen bilden sich die 4a-Addukte 8M, die auch durch 0-Alkylierung und Pummerer-Umlagerung aus 7b entstehen. Redox Reactions of l O H -~d o I 5 , 4 b ] [ l , 4 ] b e~o t~~~e sThe structure, spectral data and reactivity of the molecular species participating in the thia-alloxazine redox system are described. le-oxidation of 2 yields the radicals 4 and 5. By further oxidation or disproportionation the cation 6 is obtained, which is unstable except in concentrated acids. Addition of nucleophiles occurs in positions S(5) or C(4a). Hydrolysis of 6yields either the pseudobase 8a or the sulfoxides 7 depending on the pH. The sulfoxides 7 are obtained independently by H202 oxidation. Alcohols form 4a-adducts 8b-f, obtained also from 7b by 0-alkylation and Purnmerer rearrangement. Fur die Dihydrostufe (RED) des zweistufigen Redoxsystems 1 wurde in Reaktionen mit Elektrophilen einqualitativ ahnliches Verhalten nachgewie~en~-~). Wie fur das Thia-isoalloxazin (lb,R 5-Thia-alloxazin-RadikaleUrn die Bildung und die Reaktivitat der aus 2 und 3 (Schema 2) abgeleiteten Radikale SEM+. 4 und SEM, 5 zu untersuchen, wurden verschiedene Methoden herangezogen. Das