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The binding of substrates and inhibitors to the metal center of myoinositol monophosphatase
Author(s) -
Francis Kwok,
Jorge E. Churchich
Publication year - 1994
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(94)00506-0
Subject(s) - luminescence , chromophore , chemistry , substrate (aquarium) , metal , binding site , lanthanide , acceptor , phosphate , excited state , stereochemistry , ion , crystallography , photochemistry , biochemistry , materials science , organic chemistry , biology , ecology , physics , optoelectronics , nuclear physics , condensed matter physics
The synthetic substrate anthraniloyl‐β‐glycerol‐P binds to myoinositol monophosphatase with a K d = 5 μM at pH 7.5. The anthraniloyl chromophore, excited at 330 nm, sensitizes the long lived luminescence of bound Tb(III) at 490, 545, 585 and 620 nm. Assuming a mechanism of radiationless energy transfer, the actual distance of separation between the donor‐acceptor pair was calculated to be R = 10A˚. TB(III) binds to the monophosphatase with a K d = 2 μM, whereas Ca‐(II) displaces the lanthanide at concentrations above 0.1 mM. The binding studies support the notion that Tb(III), CA(II) and MG(II) interact with a common binding site on the protein. Phosphate ion, a strong competitive inhibitor, perturbs the luminescence of bound Tb(III), whereas the substrate β‐glycero‐P has no effect on the luminescence yield and long‐lived emission of bound Tb(III). It is suggested that the phosphate group of the substrate is not in direct contact with the metal ion coordinated to several amino acid residues of the enzyme.