Purification and Characterization of Cutinase fromVenturia inaequalis

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Abstract
Venturia inaequlais was grown in a culture medium containing purified apple cutin as the sole carbon source. After 8 wk of growth an esterase was isolated from the culture fluid and purified to apparent homogeneity. The enzyme hydrolyzed tritiated cutin and thus was identified as cutinase. The purified cutinase is a glycoprotein with a molecular mass of 21-23 kg/mol, as determined by various procedures. Remarkable structural features are a high content of glycine, a high content of nonpolar amino acids, two disulifide bridges, and a high degree of hydrophobicity. Cutin hydrolysis by cutinase from V. inaequalis is optimal at a pH of 6 thus different from the alkaline pH-optimum reported for other purified cutinases. The hydrolysis of the model ester p-nitrophenyl butyrate was less affected by the pH. The esterase activity was strongly inhibited by diisopropyl fluorophosphate, and the phosphorylation of one serine was sufficient for complete inhibition. Thus, cutinase from V. inaequalis belongs to the class of serine hydrolases, a characteristics shared with other fungal cutinases.