A 5 Transformation and Degradation of Secondary Products

For a long time metabolic stability was thought to be a characteristic of secondary products. Recent experiments, however, have demonstrated that many secondary substances are transformed or are even degraded to compounds of primary metabolism. Three types of secondary compounds may be distinguished with respect to metabolic stability (a) the truely metabolically inert end products, (b) the products stable at a given physiological or developmental state, and (c) the substances undergoing continuous turnover. 

Many secondary products are in one way or another metabolic intermediates. Of importance in further transformation are  

In several instances polymeric substances arise during the transformation of secondary products, such as polymeric carbohydrates (D 1.4.1), humic acid-like polyphenols (D 3.3.1), rubber (D 6), sporopoUenins (D 6.5), polymeric products derived from 3-hydroxyanthranilic acid (D 8.4.1), melanins (D 22.1.3), lignins (D 22.2.3), and muramin (D 23.4). Many of these compounds are formed by oxidative polymerization catalyzed by phenoloxidases (C 2.3.1) and peroxidase 

As shown in Fig. 10 after administration of the precursor C-phenylalanine the specific activity of chlorogenic acid first increases rapidly and then decreases with a half-life of less than 20 h in spite of a slight increase in its absolute amount. This indicates on the one hand steady synthesis of the new unlabeled compound and on the other hand its continuous degradation. 

Group of substances Individual compounds Half-life Organism/organ 

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