Wheat lysine synthesis

Humans can synthesize only 10 of the 20 amino acids needed for protein synthesis. The remaining 10, called essential amino acids, must be obtained from the diet and consumed on a regular, almost daily basis. Diets that include animal products readily supply all the needed amino acids. Because no one plant source has sufficient amounts of all the essential amino acids, vegetarian diets must be carefully balanced. Grains—wheat, rice, and corn—are low in lysine, and legumes— beans, peas, and peanuts— are low in methionine, but a combination of these foods provides all the needed amino acids. Thus, a diet of corn tortillas and beans, or rice and tofu, provides all essential amino acids. A peanut butter sandwich on wheat bread does, too. 

This protein has been found to be methylated immediately after its synthesis in fungi and higher plants (for a review see Paik, Polastro, and Kim, 1980). The products of the reaction are trimethyllysine residues at positions 72 and 86. The enzyme specific for methylation of lysine-72 has been purified from wheat germ (DiMaria, Kim, and Paik, 1982). Differences between the behavior of methylated and unmethylated cytochrome c suggest that methylation may lead to enhanced mitochondrial import and binding to the mitochondrial inner membrane (Park, Frost, Tuck, Ho, Kim, and Paik, 1987). 

USE Pood enrichment. Supplementation of wheat-based foods with lysine improves their protein quality and results in improved growth and tissue synthesis Peldberg. Hetzel, Food Technol. 12, 496 (1958). Method of incorporation Hause, Todd. U.S. pat. 3,015,567 (1962 to du Pont). THERap cat Nutrient. 

Seven enzyme catalyzed reactions are required for the synthesis of lysine from pyruvate and aspartate semialdehyde as illustrated in Fig. 3. However, enzymes catalyzing only the first and last of these reactions have been isolated from plants. Dihydropicolinate synthase facilitates the condensation of the precursors during a reaction which presumably proceeds in two steps. A double bond between the C-4 of the semialdehyde and the methyl carbon of pyruvate would be formed, with the loss of water, followed by spontaneous ring closure and the loss of a second molecule of water. Catalysis of this reaction in plant extracts was first demonstrated by Cheshire and Miflin (1975) using maize seedlings as the source of the enzyme. Mazelis et al. (1977) detected the enzyme in extracts obtained from six different taxonomic families of plants and partially purified the enzyme from wheat germ. Only the L isomer of aspartate semialdehyde was active as a substrate of this enzyme and strong cooperativity was noted when the concentration of pyruvate was varied. A dihydropicolinate synthase has also been isolated from carrot cells (Matthews and Widholm, 1978). 

Amino acids that the body cannot synthesise must be obtained entirely from food. These amino acids are called essential amino adds. Essential amino acids are routine constituents of most protein-based foods or dietary proteins and are fairly readily available in a reasonably well-balanced diet. However, there are some amino acids that are present in lower concentrations than the same amino acid in a high quality protein (e.g. lysine in wheat and eggs). These amino acids are called limiting amino adds, because if a person s diet is deficient in one of them, this amino acid will limit the usefulness of the others (and will limit the extent of protein synthesis in the body), even if the others are present in what would otherwise be large enough quantities. Limiting amino acids are distinct from non-essential amino acids that the body can synthesise and are therefore sometimes used for food and animal feed enrichment. 

Lysine is an essential amino acid that is mainly provided by meat products and is therefore limited in diets where wheat is the primary protein source. Lysine is also the first rate-limiting amino acid in milk-fed newborns for growth and protein synthesis. Lysine is catabolized to glutamate and acetyl-CoA and is also the precursor for the synthesis of carnitine, which is needed for mitochondrial oxidation of long-chain fatty acids. 

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