Polyproline (Poly-Pro) that is an amphiphilic polypeptide, or polytyrosine (Poly-Tyr) that is a hydrophobic polypeptide, were connected to the carboxy terminus of Pseudomonas sp. esterase by the recombinant DNA technique. The hydrophobicity of the esterase was enhanced by the introduction of Poly-Pro or Poly-Tyr, and also by increasing chain length of the polypeptides. Poly-Tyr increased the hydrophobicity of esterase more than Poly-Pro. Poly-Tyr induced significant conformational change of fusion esterase, but Poly-Pro did not. Consequently, the introduction of Poly-Tyr led to loss of activity of the fusion enzyme to a negligible level. On the other hand, the Poly-Pro-fusion-esterase retained enzymatic activity and the hydrolytic activity (k(cat)/K-m) of the fusion esterase carrying 40 proline residues (esterase-Pro40) relative to that of the wild-type esterase with the substrates p-nitrophenyl-propionate, -pentanoate, and -hexanoate was 1.76, 1.95, and 4.7, respectively. The results could be explained in terms of easier access of long-chain carboxylate to the fusion esterase compared to the wild-type esterase in aqueous solution. (C) 1998 Elsevier Science B.V. All rights reserved.