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 spores of the fungus Phomopsis viticola. Incorporation studies were performed with 3 muM S-35-degrees during the pregermination period of P. viticola spores. The free sulphur amino acids and protein sulphur amino acids were purified by column and thin-layer chromatography. During the first minutes of the pregermination process of the spores, the S-degrees was essentially metabolized into free cysteine and glutathione. Detectable concentrations of methionine and homocysteine were measured after 1 h of incubation. Azide (2 mM final concentration), an inhibitor of the mitochondrial respiratory chain at the level of cytochrome oxidase, strongly inhibited the incorporation of S-degrees. In contrast, the uncoupler 2,4-dinitrophenol (15 muM final concentration) and sulphate did not affect the incorporation of S-degrees. The metabolism of S-35-degrees into the protein sulphur amino acids cysteine and methionine during the germination of spores of P. viticola and conidia of Neurospora crassa is also discussed. It appears that S-degrees does not necessarily have to be oxidized to sulphate prior to its incorporation into sulphur amino acids, but could be directly reduced to sulphide at the level of the respiratory chain.