Agmatine putrescine formation

The first key step in the biosynthesis of tropane alkaloids is the formation of the intermediate putrescine. Polyamines and, therefore putrescine, are found in plant cells and are implicated in growth, root, fruit and flower development, and in different stress phenomena. It is well known that plants synthesize polyamines from ornithine and arginine, unlike other eukaryotes like mammals, which only synthesize polyamines from ornithine. In plants putrescine is synthesized directly from ornithine, a reaction catalysed by ornithine decarboxylase (ODC, EC 4.1.1.17) and indirectly from arginine via agmatine catalysed by arginine decarboxylase (ADC, EC 4.1.1.19), Fig. (1). In Arabidopsis, it is known that the adc gene is required for the production of polyamines that are essential for normal seed development [103]. 

The A-methyl-A -pyrrolinium cation is the last common intermediate in both tropane alkaloid and nicotine biosynthesis (Scheme 3). A-Methyl-A -pyrrolinium cation formation begins with the decarboxylation of ornithine and arginine by ornithine decarboxylase (ODC) and arginine decarboxylase (ADQ, respectively. Putresdne is formed directly from ornithine by ODC, whereas agmatine and A-carbamoylputresdne serve as intermediates when putrescine is formed via ADC. An ODC cDNA isolated from Datura stramonium showed similarity to ADCs and other ODCs 127). ADC cDNAs have been isolated from oat and tomato 128,129). Arginine appears to supply most of the putrescine for alkaloid biosynthesis (l30). 

Ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) are the first enzymes involved in the formation of tropane alkaloids (TPAs) snch as atropine and cocaine (Fig. 3). Decarboxylation of ornithine yields pntrescine, whereas arginine is converted to agmatine, which is metabolized to putrescine via a second rente. ADC is assnmed to play the primary role in TPA synthesis [18]. 

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