Abstract
Cell aggregation in Dictyostelium discoideum is mediated by chemotaxis to cyclic AMP. Aggregative cells of the simpler species D. lacteum are not attracted by this cyclic nucleotide. We describe how the cell aggregation-inducing factor, or acrasin, of D. lacteum was purified from aggregating amoebae and characterized. The acrasin, which is mainly secreted in the aggregative phase, is identified as a derivative of pterin. This identification is based on (i) its UV spectrum, (ii) the inhibition of the enzymatic degradation of acrasin by 6-methylpterin, (iii) the antagonistic effect of 6-aminopterin on chemotaxis towards both pterin and acrasin and not on the response towards folic acid or cyclic AMP, and (iv) the degradation of the acrasin to pterin. Its chromatographic properties show that the acrasin is an as yet unidentified pterin derivative. The acrasin is species specific and attracts cells at very low concentrations (0.1-0.01 microM). Also, several naturally occurring stereoisomers of 6-polyhydroxyalkylpterins attract aggregative cells at these low concentrations. Additionally, we identified a pterin deaminase, which converts pterin into 2-deamino-2-hydroxypterin (lumazin), as the acrasinase in D. lacteum.