Role of Lysine in Carnitine Biosynthesis in Neurospora crassa

Abstract Neurospora crassa lysine auxotroph strain 33933 was grown on a carnitine-free synthetic medium with either dl-[6-14C]lysine (Experiment 1), or dl-[1-14C]lysine (Experiment 2) together with 0.2 mm dl-lysine sufficient for ample growth. Carnitine was then purified from mycelial extracts of the mold by ion exchange chromatography and examined for radioactivity. In Experiment 1, radioactivity derived from [6-14C]lysine was incorporated into carnitine without dilution; and the radioactivity in such carnitine could not be dissociated from carnitine following thin layer chromatography. In contrast, radioactivity from dl-[1-14C]lysine, Experiment 2, was not detected in biosynthesized carnitine. These data thus provide evidence for the direct involvement of a portion of the lysine molecule in carnitine biosynthesis in N. crassa. A rationale for a lysine:carnitine-precursor:product relationship is offered in terms of recently discovered e-N-methyl lysine derivatives.