Lactone-forming carboxylesterases, specifically catalyzing intramolecular transesterification, but not hydrolysis. Involved in the biosynthesis of tulipalins, defensive chemicals that show antimicrobial activities against a broad range of strains of bacteria and fungi. Substrates are 6-tuliposide A > 6-tuliposide B (By similarity). 6-tuliposide A = D-glucose + tulipalin A Homodimer. 6-tuliposide A and tuliposide A-converting enzyme, which are compartmentalized in the vacuoles and plastids respectively, come into contact with each other for the enzyme reaction releasing toxic tulipalin A upon cell disruption by pathogen infection or herbivore predation. Belongs to the AB hydrolase superfamily. No genomic clone corresponding to this cDNA could be found.