Table 1.

Site-specific association equilibrium constants (K_a) measured for repaglinide at Sudlow sites I and II of normal or modified HSA^a

Type of HAS	Sudlow site I Ka (M−1)	Change vs. Normal HSA	Sudlow site II Ka (M−1)c	Change vs. Normal HSA
Normal HSA	4.2 (± 0.3) × 104	------	6.1 (± 0.2) × 104	------
GoHSA1	5.4 (± 0.5) × 104	↑ 1.29-fold	1.4 (± 0.1) × 105	↑ 2.30-fold
GoHSA2	7.2 (± 0.3) × 104	↑ 1.71-fold	2.1 (± 0.4) × 105	↑ 3.44-fold
MGoHSA1	3.8 (± 0.4) × 104	↓ 9.5% (N.S.)b	1.8 (± 0.2) × 105	↑ 2.95-fold
MGoHSA2	3.4 (± 0.4) × 104	↓ 19%	2.2 (± 0.2) × 105	↑ 3.61-fold

^aThese results were measured at 37 °C in pH 7.4, 0.067 M potassium phosphate buffer. The values in parentheses represent a range of ± 1 S. D. Except were indicated otherwise, all changes shown for modified HSA vs. normal HSA were significant at the 95% confidence level based on the Student’s t-test.

^bThe result for MGoHSA1 at Sudlow site I was not significantly different (N.S.) from normal HSA at the 95% confidence level but was significantly different at the 90% confidence level.

^cThe listed result for normal HSA is consistent with values obtained for several columns and batches of silica that contained this immobilized binding agent.