Sedimentation Equilibrium Analysis of Protein Interactions with Global Implicit Mass Conservation Constraints and Systematic Noise Decomposition Jennifer Vistica a , Julie Dam b , Andrea Balbo a , Emine Yikilmaz c , Roy A. Mariuzza b , Tracey A. Rouault c , and Peter Schuck a * a Protein Biophysics Resource, Division of Bioengineering & Physical Science, ORS, OD, National Institutes of Health, Bethesda, Maryland, USA, b Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland, USA, c Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, USA Running Title: SEDIMENTATION EQUILIBRIUM Keywords: protein interactions, heterogeneous association, protein complexes, analytical ultracentrifugation, molar mass distribution Category: Physical Techniques * Corresponding Author: Dr. Peter Schuck National Institutes of Health Bldg. 13, Rm. 3N17 13 South Drive Bethesda, MD 20892-5766,USA Phone: 301 435-1950 Fax: 301 480-1242 Email: pschuck@helix.nih.gov