1. Nutrient Requirements and Functions Laboratory, Beltsville Human Nutrition Research Center, USDA, ARS, Bldg 307C, Rm 223, Beltsville, Maryland 20705-2350, Nuclear Magnetic Resonance Laboratory, ARS, USDA, Beltsville, Maryland 20705-2350, Food Composition Laboratory, Beltsville Human Nutrition Research Center, USDA, ARS, Beltsville, Maryland 20705-2350, and Department of Molecular Cellular and Developmental Biology, University of California, Santa Barbara, California 93106-9610