In the previous papers, we reported the isolation, purification and some nature of a potent spore germination inhibitor from the cellular slime mold, Dictyostelium discoideum, 1 and subsequently presented the partial structure consisting of 6-(3-methyl-2-butenylamino)purine moiety and an unknown α-amino acid residue which was most possibly substituted at the N-3 position of the purine ring. 2 Recently we have developed an improved isolation procedure described herein for structure determination. In this paper, we wish to present the structure of the inhibitor which we name discadenine, as 3-(3-amino-3-carboxypropyl)-6-(3-methyl-2-butenylamino)purine(I). Discadenine is the first natural purine derivative possessing a α-amino acid residue on the 3-position of the purine ring. Besides its pronounced spore germination inhibitory activity, discadenine exhibits significant cytokinin activity (approximately two-thirds level of kinetin at 2.3 x 10^-7 M) in the standard tobacco pith test.