Uptake of amino acids by the marine centric diatom Cyclotella cryptica.

Abstract

The transport systems for all of the amino acids studied, with the exception of isoleucine, obey saturation kinetics. The strong inhibition of the process by cyanide and dinitrophenol provides evidence that energy is required. Additional evidence for the requirement of energy for amino acid transport is the strong temperature dependence (Q10 about 2) and the high concentration ratios measured for transported amino acids.Transport parameters (Ks and Vmax) for several amino acids were determined from data for two different concentration ranges. The results of the kinetic studies indicate the presence of two or more transport systems that become saturated at different substrate concentrations for each of the amino acids. The presence of a high affinity – high capacity transport system for arginine indicates that this amino acid may be utilized efficiently by the diatom when present at low concentrations in the natural environment.Interactions between pairs of amino acids suggest that several transport systems are available. There appears to be one system for ornithine and arginine, one for glutamate and aspartate, and several for neutral amino acids.Restriction of nitrogen in the growth medium produces a marked increase in the rate of amino acid uptake, indicating that amino acids are acquired more rapidly from the medium by nitrogen-limited cells.