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The Role of Vitamin B 12 Binding In the Uptake of the Vitamin By Euglena Gracilis
Author(s) -
SARHAN F.,
HOUDE M.,
CHENEVAL J. P.
Publication year - 1980
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1980.tb04688.x
Subject(s) - euglena gracilis , euglena , chloroplast , biochemistry , saturation vapor curve , kinetics , biology , binding site , vitamin , chemistry , biophysics , enzyme , gene , physics , quantum mechanics
The uptake of [ 57 Co]B 13 (cyanocobalamin) by Euglena gracilis strain Z (ATCC 12716) occurred in 2 distinct phases‐an initial rapid phase followed by a slower secondary phase. This secondary phase appeared after the saturation of the binding sites involved in the initial rapid phase and was energy‐dependent and completely inhibited by 2,4‐dinitrophenot, KCN and sodium azide. the subcellular localization of labeled cyanocobalamin taken up by the cell was mostly contained in the chloroplast fraction. the time course and the saturation kinetics of B 12 uptake by purified chloroplast fraction indicated that this fraction and the intact cell had a similar affinity for the vitamin B 12 . This suggested that the chloroplasts contained the binding sites for vitamin 12 and might regulate the uptake process in the intact cell. the kinetic properties of the overall 12 uptake mechanism suggested that the initial phase represent the binding of vitamin 12 to the available sites on the chloroplast. the secondary phase may represent the de novo synthesis of new binding sites.