The Chemical Classes of Zoochrome

Abstract

The structural formulae of representative members of each of the fully characterised chemical classes of zoochrome are given in Fig. 3.1. The number of known classes is small and conforms to the general law of biochemical austerity (Lwoff, 1944; Florkin, 1960; Needham, 1965 b) which governs the exploitation of materials by living organisms. The melanins, fuscins and simple metalloproteins are not represented since the structure of their chromophors is still uncertain or unknown. In addition there may be representatives of further chemical classes among the many animal pigments not yet analysed. On the other hand some of those represented are interrelated, for instance the porphyrins and bilins and the purines, pterins and isoalloxazines. Plants have certain other classes and subclasses, as well as a greater variety within some classes; this variety has its parallel in other biochemical fields such as the alkaloids, the essential oils, etc. In general biochemical austerity is more evident in animals than in plants and microorganisms, though in one respect biochromes present an exception: there are more classes in animals than in plants. Austerity seems to be greatest in materials with a fundamentally important function and this criterion helps to decide the relative importance of the various classes of zoochrome.