1. State Key Laboratory of Phytochemistry and Plant Resources in West China; Kunming Institute of Botany, Chinese Academy of Sciences; Kunming Yunnan 650201 China
2. National Magnetic Resonance Facility at Madison, Department of Biochemistry; University of Wisconsin-Madison; Madison WI 53706 USA
3. School of Molecular Biosciences, College of Veterinary Medicine; Washington State University; Pullman WA 99164 USA
4. Department of Biochemistry; Virginia Polytechnic Institute and State University; Blacksburg VA 24061 USA