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Uptake of l ‐Phenylalanine in Synchronous Chlorella fusca. Characterization of the Uptake System
Author(s) -
PEDERSEN ÅSE GRAN,
KNUTSEN GJERT
Publication year - 1974
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1974.tb03138.x
Subject(s) - phenylalanine , amino acid , chlorella , membrane filter , kinetics , biochemistry , chemistry , chromatography , biology , membrane , botany , algae , physics , quantum mechanics
Phenylalanine uptake in Chlorella fusca was measured, using the membrane filter technique. The cells were synchronized, and harvested at specific points of the life cycle. Experiments with autospores showed that the uptake followed saturation kinetics, with a K m = 5 μ M . V max , was 0.1 nmol/min × 10 7 cells. The optimum temperature for the uptake was 40°C, and the activation energy was 1700 J/mol. The uptake showed a high specificity towards l ‐phenylalanine; presence of the unlabelled stereoisomer did not inhibit the uptake. Uptake of l ‐phenylalanine was inhibited in the presence of other analogues or other amino acids, but only if they were present in concentrations considerably higher than that of L‐phenylalanine. Variations in the ratio of Na4 + to K + in the external solution during uptake experiments did not have any influence upon the uptake rate of l ‐phenylalanine. The cells were able to take up the amino acid against a concentration gradient. At pool maximum the ratio between internal and external amino acid concentration was 1000/1. 2,4‐Dinitro‐phenol inhibited the uptake completely. Exchange between internal and external l ‐phenylalanine could not be demonstrated. The K m value did not change during the life cycle of the cells. The uptake rate reached a maximum at the end of the light period, and fell to a minimum just before sporulation started. It is concluded that Chlorella fusca cells have a highly specific, active uptake system for l ‐phenylalanine. The system is constitutive, independent on the K or Na concentration, and the mechanism of uptake does not change during the life cycle of the cells.