1. Eötvös Loránd University, Department of Theoretical Chemistry, H-1518, Budapest 112, P.O. Box 32, Hungary, Gedeon Richter Ltd., Department of Computer Assisted Drug Discovery, H-1475, Budapest, 10. P.O. Box . 27, Hungary, and Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, H-1518 Budapest, P.O. Box 7, Hungary