[Preparation of a novel targeted MR contrast agent Gd-DTPA-streptavidin and exploration of its reaction conditions].

OBJECTIVE: To explore the optimal reaction condition of DTPA-coupled streptavidin labeled with gadolinium ion. METHODS: The number streptavidin-coupled of gadolinium ions and maximum biotin-binding capacity of Gd-DTPA-SA complex were analyzed at different DTPA-to-SA molar ratios (1000, 500, 200, 100) and in buffer solutions of different pH values (pH 5, 6, 7, and 8, respectively). RESULTS: The number of streptavidin-coupled gadolinium ions increased with the pH value of the reaction system. When the DTPA-to-SA molar ratio was below 500, the number of gadolinium ions that SA-DTPA coupled increased with the DTPA-to-SA molar ratio, but tended to decrease when the ratio was 1,000. No significant difference in the maximum biotin-binding capacity of Gd-DTPA-SA complex was noted between the groups. CONCLUSIONS: The number of gadolinium ions that streptavidin coupled depends on the pH value of the reaction system and DTPA-to-SA molar ratio, but the maximum biotin-binding capacity of Gd-DTPA-SA complex is not affected by the reaction conditions.