Abstract:A simple method for the preparation of heterocysts from blue-green alga Anabaena variabilis was described. The vegetative cells were disrupted by vibration at 30℃ in a buffer solution containing digitonin plus mannitol (0.3% digitonin, 0.7 M mannitol, 10 mM EDTA-Na and 10mM TES pH 7.8) for 50 min. In combination with differential centrifugation, isolated heterocysts of 90% purity were obtained. The isolated heterocysts reduced acetylene in darkness when ATP and Na2S2O4 were supplied. The activity was linear under dark for more than 4 hours and reached a maximum of 5.31n mol C2H2/106 heterocysts per hour which was 10% of the activity of the intact algae filaments on the basis of their heterocysts. Under light with H2 supply, the light dependent acetylene reduction activity was not detectable. Fluorescence spectrum from the isolated heterocysts was studied at 77˚K (exciting beam at wavelength near 430 nm). The results show that the heterocysts contain PSⅠ but Lack in PSⅡ. The DCIP+ascorbate→methyl viologen activity of this isolated heterocysts was 360 μ mol O2 consumed/mg Chl. h. The above results indicate that isolated heterocysts by this method possess an activity of PS Ⅰ of DCIPH2→MV photosynthetic electron transport.