Specificity of papaya lipase in esterification with respect to the chemical structure of substrates

Esterification, catalyzed by papaya (Carica papaya) lipase (CPL), was studied with various alcohols and carboxylic acids under competitive conditions. Acids studied were straight-chain saturates of different chain lengths, with octanoic acid as the reference. Alcohols chosen were aliphatic straight-chain, branched, secondary, tertiary, terpene, and aromatic alcohols of different chain lengths, using 1-hexanol as the reference. The initial reaction rate increased with increasing chain length of the acid from C4:0 to C18:0, followed by a slight decrease with C20:0. In the case of alcohols, an optimum chain length of 8 carbon atoms was obtained for the straight-chain aliphatic group (C2 to C16). Ethanol, 1-propanol, and secondary and tertiary alcohols showed rather low reactivity. Branching of the alcohols was found not to affect the reactivity in esterification; among the terpenes, beta-citronellol [(2E)-3,7-dimethyl-6-octenol] and geraniol [(2E)-3,7-dimethylocta-2,6-dien-1-ol] were found to be more reactive than nerol [(2Z)-3,7-dimethylocta-2,6-dien-1-ol]. The highest reaction rate was found for the aromatic benzyl alcohol (phenylmethanol).