A pantothenate derivative is covalently bound to mitochondrial proteins in Neurospora crassa

The presence of protein-bound pantothenate in Neurospora crassa was investigated by labelling a pantothenate auxotroph (pan-2) with [14C]pantothenate and examining mycelial homogenates on dodecyl sulfate/polyacrylamide gels. Five peaks of radioactivity were found, with apparent molecular masses of 200, 140, 22, 19, and 9 kDa. The 200-kDa peak was identified as fatty acid synthetase, based on its absence in a fatty acid synthetase mutant. The 22-kDa and 19-kDa peaks co-purified with mitochondrial markers on sucrose gradients. When purified mitochondria were fractionated, the 19-kDa protein was associated with the inner membrane and the 22-kDa protein was enriched in the soluble mitochondrial fraction. The label was quantitatively recovered from the mitochondrial proteins as 4'-phosphopantetheine after mild alkaline hydrolysis. Although the function of this post-translational modification of mitochondrial proteins is not known, several possibilities are discussed: the 4'-phosphopantetheine may act as a carrier group in an enzymatic reaction, or it may perform a regulatory function as part of an enzyme complex.