Cytosolic iron superoxide dismutase is a part of the triacylglycerol biosynthetic complex in oleaginous yeast

A novel multienzyme complex for the biosynthesis of triacylglycerol in oleaginous yeast has been identified recently in the cytosol and characterized [Gangar, Karande and Rajasekharan (2001) J. Biol. Chem. 276, 10290-10298]. Screening the library of Rhodotorula glutinis with an oligonucleotide probe derived from the N-terminal sequence of one of the protein components in the complex (21 kDa protein) resulted in the isolation of a 0.7 kb cDNA. Nucleotide sequence analysis revealed that the isolated gene codes for superoxide dismutase (SOD). Atomic absorption spectroscopy and inhibition assays showed that this cytosolic SOD utilizes Fe as its cofactor. Enzymic assays, immunoprecipitation and cross-linking experiments revealed that SOD is a part of the triacylglycerol biosynthetic complex, which could protect the substrate and the complex from oxidative damages. These results indicate for the first time the presence of iron-containing SOD in a soluble form in yeast.