Oxalate binding protein from the kidney of rat and human mitochondria: studies on properties

The oxalate binding protein of rat and human kidney mitochondria were extracted by Triton X-100 and purified on Sephadex G-200 column followed by HPLC. Their molecular masses were found to be 62 kD and 58 kD respectively, rich with arginine and acidic amino acids, 7% of carbohydrates and 1% of inorganic ions. Antibodies raised to the rat protein inhibited the oxalate binding and cross-reacted to the human protein as well as rat liver protein. The binding of oxalate to the protein was rapid, reversible, dependent on concentration of oxalate, temperature sensitive and inhibited by oxalate analogues. The saturation reached at 175 nM oxalate for rat protein with a Kd of 33.3 nM and Bmax of 21 nmoles while for human protein the saturation reached at 183 nM oxalate and had a Kd of 41 nM and Bmax of 14 n moles. The half-saturation concentration of inhibitor (IC50) of oxalate was 0.25 microM for rat protein and 0.225 microM for human protein while the structural analogues of oxalate had higher IC50 values. Proteoliposomes showed accumulation of oxalate confirming transport function of the protein. The rat protein promoted calcium oxalate crystallization in vitro better than that of human protein and antibody inhibited the crystal growth in vitro.