[Substrate specificity of acylase I from pig kidney]

The substrate specificity of acylase I from pig kidney has been studied. For the N-acetyl derivatives of D,L-amino acids with an unbranched side chain the catalytic efficiency of enzymatic hydrolysis increases linearly with an increase of the substrate hydrophobicity. The tangent of the linear dependence of logarithm of the second order rate constant of enzymatic hydrolysis on the Hansch hydrophobicity constant is 0,7. This supports a simple "extraction" model of energy realization during the enzyme binding to the substrate in the course of the reaction. When the amino acids with a branched side chain are used, the efficiency of hydrolysis of N-acetyl derivatives decreases by one order of magnitude as compared to the amino acids with an unbranched side chain having the same number of carbon atoms. The N-acetyl derivatives of aromatic amino acids are hydrolyzed in a small degree. An analysis of the substrate specificity of pig kidney acylase I demonstrates that the enzyme has a narrow hydrophobic "cleft" with the length not less than four metrylene links.