On biochemical variability and innovation.

Examples of variability and apparent innovation presented in this paper are but a portion of the many examples in the literature. Thus, the notion of the "unity of biochemistry" has been advanced in an overly simplified form and reflects a primitive stage in the development of the discipline. Cells contain many more compounds and biosynthetic mechanisms than we had suspected or list in our texts. Accordingly, either early chemical evolution was far more extensive than we have postulated or an evolution of biochemical synthesis and function took place which was more extensive than has been postulated; perhaps both have occurred. The chemical choices available from the environment have been considerable rather than limited and the cells have chosen, adapted, improved upon a limited number of these, and in turn have themselves been selected. In the case of the naturally occurring antibiotic substances, biosynthetic mechanisms for compounds which do not fit within the cells' own nucleic acids and proteins to advantage have nevertheless been preserved since they contribute to survival. On the other hand, some of these compounds such as alpha-ribazole, are fitted to other metabolic uses. The existence of the large number of uncommon relatives of the common components of the nucleic acids and proteins in turn implies an enormous untapped area of potential knowledge concerning their paths of biosyntheses and the genetic and physiological controls for these same paths. That these compounds exist perhaps also indicates an expanded material basis for a continuing biochemical evolution.