Bioelectrochemistty and Bioenergetics, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE 10 (1983) 289-300 A section of J. Electroanal. Chem., and constituting Vol. 155 (1983) Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands 289 zyxwvutsrqpo 572-BINDING OF OXOVANADIUM(V) ANION TO BOVINE SERUM ALBUMIN, HUMAN SERUM ALBUMIN AND BOVINE PANCREATIC TRYPSIN J.P.S. ARORA, R.P. SINGH, D. SOAM, S.P. SINGH and R. KUMAR Chemistry Department, D.A. V. (P. G.) College, Muzaffarnagar - 251001 (India) (Manuscript received January 20th 1983) SUMMARY The binding of vanadium(V) to bovine serum albumin (BSA), human serum albumin (HSA), and bovine pancreatic trypsin in the absence and presence of urea has been studied at different pH values and temperatures by spectrophotometric and equilibrium dialysis methods. The binding data were found to be pH and temperature dependent. The binding data at pH 5.57, studied by the absorbance method, were found approximately identical with those obtained from the equilibrium dialysis method at this pH. The enthalpy change at pH 5.57 for vanadium(V)-protein was - 368.4 cal Mole-’ for BSA, - 328.8 cal Mole-’ for HSA and - 1372 cal Mole-’ for trypsin respectively. The association constants and the number of binding sites were calculated from Scatchard plots and found to be at maximum at lower pH and at lower temperature. The free energy of the combining sites was lowest at higher pH and highest at low pH. Therefore, a lower temperature and a lower pH offered more sites in the protein molecule for interaction with vanadium(V) ions. Statistical effects seem to be more significant at lower vanadium(V) ion concentrations, and electrostatic effects more significant at higher concentrations. INTRODUCTION The biological significance of vanadium in its different oxidation states is well established [l-4]. Although in the form of vanadium(II1) it forms an integral part of haemovanadin [5,6], and as vanadium(IV) reacts with several physiologically active compounds [7-lo] as well as with metal binding sites of many proteins [ 1 l- 151, its interaction in the oxidation state (V) with macromolecules has not so far been extensively investigated, presumably due to its complicated concentration and pH-dependent equilibrium [ 16,171. In order to show that vanadate ion can occupy the same reactive sites as other anions on a protein molecule [18-211, a comparison was made of its interaction with bovine serum albumin (BSA), and bovine pan- creatic trypsin (BPT) using a polarographic method described in an earlier paper [22]. In this communication the binding results of oxovanadium(V) anion with human serum albumin (HSA), BSA and BPT are discussed using spectrophotometric and equilibrium dialysis methods. 0302-4598/ 83/ $03.00 0 1983 Elsevier Sequoia S.A.