Microcalorimetric studies on the complex formation between cellobiohydrolase I (CBH I) from Trichoderma reesei and the (R)- and (S)-enantiomers of the beta-receptor blocking agent alprenolol

The thermodynamic quantities for the complex formation between the enantiom ers of the beta-blocking drug alprenolol and cellobiohydrolase I (CBH I), t hat earlier has been used as a chiral selector for aminoalcohols, revealed positive Delta H-0 - values in all cases implying an entropy driven process . Association constants (K-a) for cellulase and the (R)- and (S)-enantiomer s of alprenolol were determined by isothermal titration microcalorimetry an d the inhibition constants (Ki) by enzyme inhibition experiments. Both inhi bition experiments and microcalorimetry revealed that the affinity between the enantiomers of alprenolol and CBH I was higher in sodium phosphate buff er than in potassium phosphate buffer. This result was in agreement with pr eviously reported liquid chromatographic separations of enantiomers using a chiral stationary phase based on CBH I immobilized to silica particles. Th e best fit of the isothermal titration data corresponded to a 1:1 binding i sotherm. (C) 2000 Elsevier Science B.V. All rights reserved.