[1] UNIV TEXAS, CLAYTON FDN BIOCHEM INST, DEPT CHEM, AUSTIN, TX 78712 USA
[2] UNIV CALIF SAN FRANCISCO, DEPT BIOCHEM & BIOPHYS, SAN FRANCISCO, CA 94143 USA
[3] UNIV CALIF SAN DIEGO, DEPT PHYS, LA JOLLA, CA 92093 USA
[4] AGOURON INST, LA JOLLA, CA 92037 USA