Secondary compounds metabolic characteristics

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. 

Phytotoxins are classical secondary metabolites and as such possess all the characteristics one would expect of such compounds. They are a) structurally heterogeneous, b) contain a variety of functional groups, c) produced by a restricted number of microorganisms, d) produced at specific phases in the growth cycle, e) highly dependent on nutritional and environmental conditions for synthesis and f) not readily metabolized. 

A characteristic feature of plants is their capacity to synthesize and store a wide variety of low molecular weight compounds, the so-called secondary metabolites (SMs) or natural products. The number of described structures exceeds 100000 the real number in nature is certainly much higher because only 20-30% of plants have been investigated in phytochemistry so far. In contrasf fo primary mefabolites, which are essential for the life of every plant, the individual types of SMs usually occur in a limited number of plants, indicating that they are not essential for primary metabolism, i.e. anabolism or catabolism. 

Polyphenols are a heterogeneous group of natural compounds, particularly known for their beneficial effects on human health. In nature, polyphenols are produced by the secondary metabolism of plants, where, in relation to their various chemical characteristics have different roles ... 

The chief function of testosterone and other androgens is to promote the normal growth of the male reproductive organs (the primary sex characteristics) and the development of the male s characteristic deep voice, pattern of body and facial hair, and musculature (secondary sex characteristics). Although testosterone produces these effects, it is not active when taken oraUy because it is metabolized in the liver to an inactive steroid. A number of oral anabolic steroids have been developed for use in rehabilitation medicine, particularly when muscle atrophy occurs during recovery from an injury. Examples include the following compounds ... 

In addition to the primary metabolic reactions which are similar in all groups of living organisms (formation and breakdown of nucleic acids and proteins and their precursors, of most carbohydrates, of some carboxylic acids, etc., cf. Table 6), a vast number of metabolic pathways lead to the formation of pecuhar chemical compounds, the so-caUed secondary products . The most characteristic features of these substances are... 

Microbial trophophase cells and embryogenic cells of higher plants and animals resemble each other in several respects. Their metabolism is well balanced and produces with optimum speed the compounds necessary for cell multiplication. Intracellular or extracellular signals, however, may cause cell division to slow down and already existing cells to specialize by forming of new cytological characteristics and synthesizing new compounds, e.g., secondary products. 

This intricate web of vital biochemical reactions is referred to as primary metabolism. It is often displayed usefully in chart form [4], and to the eye appears very much like an advanced model railway layout, not least because of the way primary metabolism proceeds in cycles (e.g. the citric acid cycle). The organic compounds of primary metabolism are the stations on the main lines of this railway, the compounds of secondary metabolism the termini of branch lines. Secondary metabolites are distinguished more precisely from primary metabolites by the following criteria they have a restricted distribution being found mostly in plants and micro-organisms, and are often characteristic of individual genera, species, or strains they are... 

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