UPTAKE AND ASSIMILATION OF AMINO ACIDS BY PLATYMONAS. II. INCREASED UPTAKE IN NITROGEN-DEFICIENT CELLS

¹ Department of Developmental and Cell Biology, University of California, Irvine, California 92664

The marine phytoplankter, Platymonas, increases rates of amino acid uptake when grown on a restricted nitrogen supply. Uptake of glycine, arginine, and glutamate increases as much as 10-fold when cells are deprived of nitrogen during growth. In a given culture, arginine uptake is always faster than glycine, and glutamate accumulation is always slowest. Nitrogen-deprivation also stimulates accumulation of non-metabolizable amino acid analogues. Kinetic studies suggest that V_max increases and K₈remains unchanged in N-deprived cells. When low concentrations of glycine or arginine are supplied to cells grown on restricted nitrogen, uptake rates are sufficient to fulfill the nitrogen requirement in Platymonas. High concentrations of nitrate or ammonia do not interfere with amino acid uptake. Thus amino acids in the ocean may be an important nitrogen source for some phytoplankters.