Oligoamines and their metabolism in the cellular slime mould Dictyostelium discoideum

Abstract

Various aspects of oligoamine metabolism in the cellular slime mould Dtctyostelium discoideum are investigated. The levels of oligoamines in D. discoideum are determined at all stages of the life cycle, The amoebae contain high levels of putrescine and 1,3-diaminopropane whilst spermidine is present but at lower concentrations. Only trace amounts of spermine are present. During development the levels of oligoamines decrease concomitantly with RNA and protein levels. No significant increase in the oligoamine content of spores is detected during germination. The biosynthetic pathway to putrescine in P. discoideum is typical of eucaryotic organisms, via decarboxylation of ornithine. High levels of ornithine decarboxylase activity are detected in amoebal extracts. Variations in extracellular osmolality result in alterations in the levels of ornithine decarboxylase activity measured. Spermidine is synthesized from putrescine and low levels of S-adenosy1-L-methionine decarboxylase activity are found in amoebal extracts. This enzyme resembles that of Physarum polycephalum and Tetrahymena pyriformis in that it is activated by neither putrescine nor magnesium. During the developmental phase the level of activity of both enzymes decreases. Amoebae concentrate extracellular putrescine at a rapid rate by an energy dependent process. A model for putrescine uptake is proposed involving adsorptive pinocytosis at low putrescine concentrations and fluid phase pinocytosis at higher concentration.