1. For a more comprehensive review see: Hinterding, K.; Alonso-Diáz, D.; Waldmann, H. Angew. Chem. 1998, 110, 716; Angew. Chem. Int. Ed. Engl. 1998, 37, 688.
2. (a) Rodbell, M. Angew. Chem. 1995, 107, 1549; Angew. Chem. Int. Ed. Engl. 1995, 34, 1420,
3. (b) Gilman, A. G. ibid. 1995, 107, 1533 and 1995, 34, 1406.
4. For a comprehensive presentation, see: (a) Lodish, H.; Baltimore, D.; Berk, A.; Zipursky, S. L.; Matsudeira, P.; Darnell, J. Molekulare Zellbiologie, 2nd edition; Walter de Gruyter: Berlin, 1996, Chapter 20,
5. (b) Krauss, G. Biochemie der Regulation und Signaltransduktion, Wiley-VCH, 1997.