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. 6-tuliposide A = D-glucose + tulipalin A kcat is 3200sec(-1) with 6-tuliposide A as substrate. kcat is 720 sec(-1) with 6-tuliposide B as substrate. Homodimer. Highly expressed in pistil and bulb scales. Lower expression in stem, and barely detected in root, leaf, petal and stamen. 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.