Substrate Specificity of Chlorophyllase

Abstract

Apparent Km and V_max values were obtained for hydrolysis of methyl and ethyl chlorophyllides a, methyl and ethyl pheophorbide a, and 9-hydroxymethyl pheophorbide a by chlorophyllase from Ailanthus altissima. Analysis of substrate specificity data for chlorophyllase indicates that the presence of a 9-keto group and a methyl alcohol group esterified at the 7-position in chlorophyll derivatives results in maximum binding affinity for substrates. Data on maximum reaction rates indicate that the rate-controlling step of hydrolysis occurs after release of the alcohol from the ester. Probable high affinity chlorophyllase inhibitors can be predicted on the basis of these specificity studies.