METABOLISM OF [N-15]ALANINE IN THE ECTOMYCORRHIZAL FUNGUS PAXILLUS-INVOLUTUS

Alanine metabolism in the ectomycorrhizal fungus Paxillus involutus wa s investigated using [N-15]alanine. Short-term exposure of mycelial di scs to [N-15]alanine showed that the greatest flow of N-15 was to glut amate and to aspartate. Levels of enrichment were as high as 15-20% fo r glutamate and 13-18% for aspartate, whereas that of alanine reached 30%. Label was also detected in the amino-N of glutamine and in serine and glycine, although at lower levels. Preincubation of mycelia with aminooxyacetate, an inhibitor of transamination reactions, resulted in complete inhibition of the flow of the label to glutamate, aspartate, and amino-N of glutamine, whereas [N-15]alanine rapidly accumulated. This evidence indicates the direct involvement of alanine aminotransfe rase for translocation of N-15 from alanine to glutamate. Alanine may be a convenient reservoir of both nitrogen and carbon. (C) 1995 Academ ic Press, Inc.