1. L. B. Townsend, Chem. Rev. 67, 533 (1967).
2. L. B. Townsend and G. R. Revankar, Chem. Rev. 70, 389 (1970).
3. J. M. Buchanan and S.C. Hartman, Adv. Enzymol. 21, 199 (1959).
4. A. L. Lehninger, Biochemistry, 2nd ed., p. 706, Worth, New York (1975).
5. R. W. Schayer, Physiol. Rev. 39, 116 (1959).