1. Physics Department, City College of the City University of New York, New York, New York 10031, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, Department of Biochemistry and Cell Biology and The Institute of Biosciences and Bioengineering, Rice University, Houston, Texas 77005, and Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461