INTERACTION OF VANADATE WITH HUMAN THROMBIN, SOME AMINO ACIDS AND ASCORBIC ACID AT PHYSIOLOGICAL pH

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Date
1994-12
Authors
ISMAILA, YAHAYA ABDULMUMIN
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Abstract
The interaction of vanadate with human thrombin some L-oc amino acids and L-ascorbic acid were studied at the physiological pH (7.40) using ultraviolet difference spectroscopy. It was concluded that thrombin specifically and reversibly binds 2 equivalents of vanadate at the metal-binding sites of the protein. The vanadium (V) - thrombin complex was formed, by addition of vanadate to thrombin. Reversibility experiments carried out using Fe(III) and Ga(III) showed displacement of bound vanadium following addition of these ions which exhibited greater interaction with thrombin compared to vanadium (V) as reflected by their higher values of molar absorptivities. The binding constant for the second equivalent of vanadate is 1048 in 0.02M phosphate buffer, pH 7.40 at 29.5°C. From these studies, vanadate binds on the metal binding sites of the thrombin as a cation analogue. The interaction of vanadate with some L-cc amino acids and L-ascorbic acid were studied at the physiological pH using pHmetric titration and ultraviolet charge transfer spectra. The most stable stoichiometric ratio of complexes formed as observed in the pH metric titrations were selected and their charge transfer spectra studied for possible binding modes. At the physiological pH, L-ascorbic acid formed a stable ML type complex with vanadate; L-histidine, L-proline and model ligands ethylamine and histamine all formed stable ML2 type complexes with the Vanadate system; L-alanine, L-aspartic acid and L-tyrosine and model ligands acetic acid and 2,3-diamino propaionic acid all formed stable ML3 type complexes with the Vanadate system; and L-threonine formed stable ML4 type complex with the vanadate system in 0.02M phosphate buffer, 0.02M ionic strength, at 29.5°C.
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A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL, AHMADU BELLO UNIVERSITY, ZARIA, IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF DEGREE OF MASTER OF SCIENCE IN CHEMISTRY (INORGANIC)
Keywords
INTERACTION, VANADAT, HUMAN, HUMAN, THROMBIN,, AMINO, ASCORBIC, ACID, PHYSIOLOGICAL, pH
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