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ARS Home » Research » Publications at this Location » Publication #103285


item LU, J
item Stipanovic, Robert - Bob

Submitted to: Biochemistry and Molecular Biology Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: We have studied the cyclization of farnesyl diphosphate (FDP) and nerolidyl diphosphate (NDP) to delta-cadinene (CAD) by a purified recombinant cotton CAD synthase expressed by E. coli. The Km for FDP was 10.4 micro M and the Km for NDP was 13.8 micro M. The labeling pattern of deuterated CAD from (1-RS)-[1-2H]-E,E)-FDP or [4,4,13,13,13-2H5]-NDP indicate the conversion of fFDP and NDP to a cisoid allylic cation-pyrophosphate anion pair, cyclization to a cis-germacradienyl cation, 1,3-hydride shift, cyclization to a cadinanyl cation and deprotonation to CAD. The products formed from the cyclization of NDP were 46.8% CAD, 18.6% beta-bisabolene and 28% alpha- bisabolol side products, and 1.3%, 2.0%, 3.3% unknowns. The formation of beta-bisabolene from NDP involves conversion to a cisoid allylic cation- pyrophosphate anion pair, cyclization to a bisabolyl cation, and deprotonation. The products formed from the cyclization of FDP were 92.1% CAD and 7.9% gamma-cadinene. No other products were detected. The product differences demonstrate that FDP is not converted to NDP prior to cyclization to CAD. The primary structures of cotton CAD synthase and tobacco epi-aristolochene synthase (TEAS) show 48% identify suggesting similar 3D-structures. We used the SWISS-MODEL and the crystal structure of TEAS to model the structure of CAD synthase. Several amino acids in the primary structures of CAD synthase and TEAS superimpose. Other amino acids having catalytic roles in TEAS are substituted in the CAD synthase and may be related to differences in catalysis. (Supported by a grant from Cotton, Inc., USDA, and the Texas Agricultural Experiment Station.)