The same pheromones apparently initiate sexual development in all mucoraceous fungi. We isolated methyl trisporates and methyl 4-dihydrotrisporates as pheromones from (+) cultures of Blakeslea trispom and used Sephadex LH-20 chromatography with ethyl acetate for the purification. The pheromones stimulated the development of zygophores (sex cells) in bioassays with (-) cultures of Phycomyces blakesleeanus and Mucor rnucedo. Labeled methyl 4-dihydrotrisporate-C and methyl trisporate-C, prepared

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... emically from labeled trisporic acid-C, were incorporated into trisporic acids in (-), but not (+), cultures of P. blakesleeanus. Two other labeled compounds, Cpd85 and Cpd76, also were isolated from the incubation with methyl 4-dihydrotrisporate-C. Cpd85 and Cpd76 apparently were not precursors of trisporic acids, zygophore-stimulating pheromones, or zygotropic pheromones, but were procedural artifacts. Methyl 4-dihydrotrisporate-C dehydrated to Cpd85 and 4-dihydrotrisporate-C dehydrated to Cpd76 in slightly acidic solutions. Cpd85 was formed when Cpd76 was treated with diazomethane. W, IR, NMR, and mass spectra verified that Cpd85 was 1,3dimethyl-2-[3-(tetrahydro-5-methyl-2-furanyl)-2-b~tenylidene]-3-cyclohexene-l-carboxylic acid methyl ester. RF and E values are given for each compound studied. We conclude that the distinguishing feature of pheromones made by (+) and ( 2 ) mating types is the degree of oxidation of the pro-S methyl group on carbon atom 1 and propose that the (+) mating type has a mechanism for inactivating trisporate precursors which would self-stimulate the formation of zygophores. Phycomyces blakesleeanus is a single-celled, multinucleate organism which responds to a variety of external signals (1-3 ) . Sexual development, for example, requires the cooperation of cultures of opposite mating types ( 3 ) . Zygophores, sexually differentiated hyphae, develop on asexual hyphae prior to cell contact in crosses of (+) and (-) wild type cultures (4). Zygophores develop only on the carotene-deficient mutants in