Acetataktivierung in grünalgen: II. Bie bildung von acetylphosphat in Stichococcus bacillaris und anderen arter der chlorococcales

Abstract

1. 1. Resting cells of Stichococcus bacillaris rapidly metabolise acetate. In contrast to former experiments with Euglena gracilis there was no lag phase in O 3 -uptake. Immediately after addition of acetate to respiring cells O 2 -uptake rose to maximum level. Only about 50% of the added acetate is oxidises, the remainder is assimilated 2. 2. Although in crude cell-free preparations acethydroxamic acid formation occurred also after CoA had been removed, there was a small stimulative effect upon adding CoA to the mixture. In reaction mixtures, however, which had been heated for 20 min to 55°, CoA had no influence on the formation of hydroxamic acid. 3. 3. In short time experiments authentic acetyl phosphate will be metabolised by crude extracts only if ADP as a phosphate acceptor is present. Exact stoichimometric relations exist between the disappearance of acetyl phosphate and ADP and the synthesis of ATP. 4. 3. All experiments performed provide strong evidence, that in Stichococcus bacillaris and some other species of Chlorococcales acetate activation is initiated by acetyl phosphate formation. The enzyme responsible for this reaction, acetate-kinase (ATP: acetate phosphotransferase, EC 2.7.2.1), has been purified. The requirements for the reaction were studied, and the Michaelis constants determined.