METABOLISM OF ELEMENTAL SULFUR (S-DEGREES) DURING FUNGAL SPORE GERMINATION

S-35-labelled elemental sulphur (S-degrees) at nontoxic levels (3 muM) was incorporated into sulphur amino acids and glutathione by the spor es of the fungus Phomopsis viticola. Incorporation studies were perfor med with 3 muM S-35-degrees during the pregermination period of P. vit icola spores. The free sulphur amino acids and protein sulphur amino a cids were purified by column and thin-layer chromatography. During the first minutes of the pregermination process of the spores, the S-degr ees was essentially metabolized into free cysteine and glutathione. De tectable concentrations of methionine and homocysteine were measured a fter 1 h of incubation. Azide (2 mM final concentration), an inhibitor of the mitochondrial respiratory chain at the level of cytochrome oxi dase, strongly inhibited the incorporation of S-degrees. In contrast, the uncoupler 2,4-dinitrophenol (15 muM final concentration) and sulph ate did not affect the incorporation of S-degrees. The metabolism of S -35-degrees into the protein sulphur amino acids cysteine and methioni ne during the germination of spores of P. viticola and conidia of Neur ospora crassa is also discussed. It appears that S-degrees does not ne cessarily have to be oxidized to sulphate prior to its incorporation i nto sulphur amino acids, but could be directly reduced to sulphide at the level of the respiratory chain.