1. Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Kita-15, Nishi-7, Kita-ku, Sapporo, 060-8638 Japan, and Laboratory for Bio-Macromolecular Chemistry, Division of Biological Sciences, Graduate School of Science, Frontier Reasearch Center for the Post-Genomic Science and Technology, Hokkaido University, Kita-21, Nishi-11, Kita-ku, Sapporo, 001-0021 Japan.