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KINETICS OF THE UPTAKE OF SOME NEUTRAL AMINO ACIDS BY SPIRODELA POLYRHIZA
Author(s) -
Borstlap A. C.
Publication year - 1977
Publication title -
acta botanica neerlandica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0044-5983
DOI - 10.1111/j.1438-8677.1977.tb01105.x
Subject(s) - valine , amino acid , leucine , efflux , glycine , alanine , kinetics , lemna gibba , biology , lemna , biochemistry , michaelis–menten kinetics , isoleucine , chemistry , botany , aquatic plant , enzyme , enzyme assay , ecology , physics , quantum mechanics , macrophyte
SUMMARY Uptake of glycine, L‐alanine, L‐leucine, L‐isoleucine, L‐valine, and D‐valine by intact fronds of the duckweed Spirodela polyrhiza was investigated.The time‐course of amino acid uptake showed that the uptake rate (= net influx) was apparently not affected by accumulation of amino acid in the fronds, suggesting that there was no trans‐inhibition of the influx, and that the efflux was negligible. Efflux was measured from fronds preloaded with L‐( 14 C)leucine. When the external and internal concentration were both about 2.5 mM the efflux was ≤ 1% of the influx. Uptake rates were measured over a wide concentration range, 1 μM to 10 mM. For each amino acid the relation between uptake rate and external concentration could be described as the sum of two Michaelis‐Menten processes. It is suggested that the duckweed possesses two transport systems common to the neutral amino acids tested: a low Km, low capacity system (system 1), and a high Km, high capacity system (system 2).