1. Loomis WF (1988) Four billion years, an essay on the evolution of genes and organisms. Sinauer Associates, Sunderland, p 286
2. Mortlock RP (ed) (1992) The evolution of metabolic function. CRC Press, Boca Raton, p 330
3. Horowitz NH (1945) Proc Natl Acad Sci U S A 31:153–157
4. Horowitz NH (1965) In: Bryson V, Vogel HJ (eds) Evolving genes and proteins. Academic, New York, pp 16–23
5. Jensen RA (1976) Ann Rev Microbiol 30:409–425