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A transitory increase in ornithine decarboxylase activity has been observed soon after food removal from Dictyostelium discoideumamoeba. This increase can be prevented by supplementation of the differentiation buffer with the 11 amino acids known for their ability to retard the development of this slime mold. Lysine can replace the amino acid mixture with an apparent inhibition constant of 50 micromolar. This inhibition by lysine, which was only observed in vivo, took place within 5 min and was readily reversed upon lysine removal.

Pretreatment of proliferating D. discoideum amoebae with 10 mM butyrate for at least 8 h (one duplicating time) induced a reversible and dose dependent premature expression of several developmental parameters when the cells were starved in the absence of the fatty acid. The aggregative phase of the morphogenetic cycle was reduced in 2 h and the appearance of mature fruiting bodies and spores took place 4 h earlier as a result of butyrate pretreatment. Some developmentally regulated proteins, such as contact-sites A, cell surface lectins and cyclic AMP phosphodiesterase were also expressed 2 h earlier in butyrate pretreated cells than in controls. The level of extracellular cyclic AMP was reduced in butyrate pretreated cells, while other parameters of cyclic AMP metabolism were not affected. Butyrate also caused a partial inhibition of growth and the hyperacetylation of histone H4 in growing amoeba. These results suggest that butyrate acts as an inducer of differentiation in D. discoideum and can therefore be used as an experimental tool in order to explore regulatory mechanisms operating in slime mold differentiation.