We inadvertently neglected to request permission for Figure 7 (Volume 8, Number 6, 1999, pp. 1166–1180), but we have received permission. The original figure is reprinted from the book Transition States of Biochemical Processes. It actually comes from Chapter 3 (Figure 1) of the book. The complete reference is: “Quantum Mechanical Approaches to the Study of Enzymatic Transition States and Reaction Paths.” Gerald A. Maggiora and Ralph E. Christoffersen, Transition States of Biochemical Processes, Edited by Richard D. Gandour and Richard L. Schowen, Plenum Press, New York, 1978, pp. 119–163 (Chapter 3).