Chemical chemotypes

Williams takes the long view. He sees the random variation among species as an engine that drives how chemotypes are fully realized as a group. This is a very different emphasis from Stephen Jay Gould s Wonderful Life (1990), which emphasizes the random walk of speciation for individuals. These two descriptions may very weU be compatible, Gould s view from up close at the organism level, and WiUiams s view from afar, across eons of time, at the chemical/chemotype level. 

There are a number of practical problems involved with using polysaccharides as vaccines as there are frequently too many different chemotypes for it to be practicable to prepare a vaccine. In some cases a limited number of serotypes are the dominant cause of infection and it may then be possible to produce vaccines. A major problem is the poor immune response elicited by polysaccharide antigens, which may in some cases be improved by chemical modification. This is (fie case for vaccines for Haemophilus influenzae type b (a causative agent of meningitis), where the antigenicity of the polysaccharide can be increased by coupling to proteins. 

Studies of the essential oils of Thymus species have documented the existence of several chemotypes with greater or lesser geographical distinctions among them. In an examination of the essential oils of T. vulgaris L. native to France, Granger and Passet (1973) described six chemical phenotypes based upon the occurrence of a number... 

The authors discounted the existence of two chemotypes of L. dulcis on the grounds that no evidence appears to exist as to this level of plasticity in this species. Rather, they suggested that the problem likely arose in the source of the Mexican specimen, which consisted of plants collected in the vicinity of Tlayacapan (Morelos) and mixed with hierba dulce purchased in a market in Mexico City. Adulteration of the commercial product, not an uncommon practice, likely accounts for the striking chemical differences between the two specimens. 

Laurencia, which has also attracted a lot of attention because of its chemical constituents, is a comparatively large genus. In addition to examples of geographically distinct chemotypes, the examples below illustrate the considerable structural variety... 

Cyperus rotundus L. is a weedy species, native to India, but widely distributed in countries on the Pacific Rim and islands in the Pacific Basin. Commonly referred to as purple nut sedge, it has been known in the Hawaiian Islands since the middle of the nineteenth century. In addition to its weedy nature, the taxon has attracted attention because of the antifebrile activity of its rhizomes. Chemical studies have disclosed the presence of several sesquiterpene derivatives, some of which have been implicated in the plant s medicinal use (cyperene and cyperinerol) (Wagner et ah, 1990, p. 1399). Our interest in this species is the existence of several chemotypes with interesting patterns of occurrence involving Pacific Rim countries and several oceanic islands, including the Hawaiian Islands, islands in the southern Pacific, and the Philippines. 

Major Chemotypic Groups Novel Chemical Characterisation and Sub-groups... 

The above description provides a possible starting background for the description of the beginning of cellular chemotypes, prokaryotes, but even this is less complicated than the only cells for which we have evidence since they have at least two additional groups of more sophisticated chemicals - coenzymes (see Tables 5.3 and 5.4) and certain metal cofactors, which we presume were additions to the most primitive cells. After we have described them, we shall return to the problem of cellular (cytoplasmic) organisation. Note that coenzyme novelty is not in basic pathways but in control of rates and in energy management. 

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