Uptake of 45Ca by mitochondria of Trigonella foenum-graecum as influenced by selenium and mimosine--detailed kinetic analyses.
Mitochondria from Trigonella foenum-graecum seedlings grown independently in the presence of either selenium (0.75 ppm) or mimosine (0.1 mM) exhibited respiration-stimulated energy-dependent uptake of Ca2+. Uptake studies were carried out independently at a series of Ca2+ concentrations at two different levels: (1) 1-20 MM and (2) 25-1,500 microM. Levels of uptake were 50-100% higher in the mitochondria of seedlings of both the Se and mimosine groups. Detailed kinetic analyses revealed negative cooperative effects operative during uptake of Ca2+ at 25-1,500 microM given in the medium. Hill coefficients for Ca2+ uptake by the mitochondria of different groups remained unchanged (nH, 0.75). Biphasic Scatchard plots were concave upward, suggestive of two classes of binding sites. High-affinity binding sites were estimated to be 16 nmol/mg protein with dissociation constant (KCa) of 2.5 x 10(9) L/mol. In contrast, graphical analyses of the uptake of Ca2+ in the range 1-20 microM in the medium revealed cooperative effects of positive nature. The present study demonstrates mixed cooperative effects during Ca2+ uptake by mitochondria from seedlings of T. foenum-graecum.
Sreekala
M
M
Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Lalitha
K
K
D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D007700:Kinetics; D008898:Mimosine / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D012643:Selenium / Q000494:pharmacology*; D029910:Trigonella / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism*
D002132:Calcium Radioisotopes; D008898:Mimosine; D012643:Selenium; D002118:Calcium