Legumes homoserine

Asparagine and glutamine are the major transport compounds found in plants, with arginine frequently being present particularly in perennials (e.g., trees). Nonprotein amino acids, homoserine, canavanine, and y-methy-leneglutamine are utilized in specific plants. The ureides allantoin and allantoic acid are frequently found in nodulated tropical legumes. 

The seed canavanine is rapidly metabolized on germination to canaline and urea [Eq. (1), Fig. 7] by the enzyme arginase which is able to catalyze the hydrolysis of both arginine and canavanine. Urea is further hydrolyzed to ammonia and CO2, the N is presumably utilized for protein amino acid biosynthesis (Rosenthal, 1970 Whiteside and Thurman, 1971). An analysis of a large number of canavanine-containing legumes showed that there was a correlation between canavanine content and urease activity (Rosenthal, 1974). There is limited evidence that canaline is further broken down to homoserine and ammonia. 

Similarities between the mechanisms by which the products of proteolysis of the endosperms of castor bean and of maize are processed and transported are evident. The involvement of homoserine may be peculiar to mobilization from the cotyledons of Pisum (or perhaps legumes) since little or no homoserine has been reported in other plants, and the full significance of this interesting digression from the norm is not yet understood. 

Various legumes (seeds of plants of the Fabaceae family) are rich sources of free aliphatic hydroxyamino acids. Common amino acids such as 4-hydroxyleucine, 4-hydroxynorvahne and 5-hydroxynorleucine are hydroxyderivatives of branched chain amino acids, L-leucine (2-4), L-isoleucine (2-4), L-norvahne (2-24) and L-norleucine (2-25). Another common amino acidinlegumes is L-homoserine (2-26), which is derived from 2-aminobutyric acid, the intermediate in the biosynthesis of threonine from aspartic acid. Frequently O-acyl- and O-amino derivatives of homoserine are seen. An example of an O-aminoderivative of homoserine is a toxic amino acid known as canaUne (see Section 2.2.1.2.4). The most common source of this amino acid is the jack bean Canavalia ensiformis). 

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