Open Accessmyo ‐Inositol oxygenase from rat kidneys
Author(s) -
KOLLER Franz,
KOLLER Elisabeth
Publication year - 1990
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1990.tb19355.x
Subject(s) - dimer , monomer , enzyme , chemistry , dissociation constant , inositol , substrate (aquarium) , reaction rate constant , dissociation (chemistry) , oxygenase , molecular mass , specific activity , stereochemistry , biochemistry , kinetics , receptor , biology , organic chemistry , ecology , physics , quantum mechanics , polymer
myo ‐Inositol from rat kidneys, an oligomeric protein with apparent molecular mass of about 270 kDa can be dissociated under mild conditions to structured 16.8‐kDa monomers. This dissociation can be reversed at high protein concentrations at room temperature. The corresponding apparent dimerization constant K 2 app = 1.38 × 10 5 M −1 , the corresponding rate constant k 2 = 350 s −1 · M −1 , and the apparent constant for the association of dimers, K 4 app = 2.7 × 10 6 M −1 . Reassociation is significantly enhanced in the presence of the substrate and iron(II) ( K 2 app = 9.8 × 10 5 M −1 ; K 4 app = 3.75 × 10 6 M −1 , k 2 = 1750 s −1 · M −1 , at 20 mM myo ‐inositol and 0.5 mM FeSO4). Under these conditions almost 100% of the original enzymatic activity was reconstituted. Monomers, with or without bound ligands, lack catalytic activity, whereas the dimer is likely to be the elementary active enzyme‐building unit. The effects of myo ‐inositol on the dimerization lead to the conclusion that this step is both mediated and facilitated by the substrate.