Transport of l-lysine in the fission yeast Schizosaccharomyces pombe

Abstract

Systems of l-lysine transport in Schizosaccharomyces pombe are not constitutive, as at no phase of growth in a rich medium is lysine taken up. Transport activity appears only after preincubation of harvested cells with glucose or another suitable source of energy. If cycloheximide is added during this preincubation no transport systems are synthesized. After removal of glucose, the activity of the transport system decays with a half-time of 13 min. The transport of l-lysine into S. pombe cells from thetionary phase of growth preincubated for 60 min with 1% d-glucose is mediated by at least two systems, the high-affinity one with a K t of 26 μmol/l and J max of 4.95 nmol/min per mg dry wt., the low-affinity one with a K T of 1.1 mmol/l and J max of 11.8 nmol/min per mg dry wt. The transport of lysine mediated by these two systems proceeds uphill. The high-affinity system has a pH optimum at 4.0–4.2, the accumulation ratio is highest at a cell density 2–5 mg dry wt. per ml and decreases with increasing lysine concentrations. Lysine accumulated by this system does not exit from cells. The only potent competitive inhibitors are l-arginine, l-histidine and d-lysine. The other amino acids tested do not behave as competitive inhibitors. Of the various metabolic inhibitors tested, the most potent were proton conductors and antimycin A.