Quality Protein Maize:  A Biochemical Study of Enzymes Involved in Lysine Metabolism

• Published in: Journal of agricultural and food chemistry Vol. 47; no. 3; pp. 1268 - 1275
• Main Authors: Gaziola, S. A, Alessi, E. S, Guimaraes, P. E. O, Damerval, C, Azevedo, R. A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-03-1999
• Subjects: Agronomy. Soil science and plant productions; Aspartate Kinase - metabolism; Biological and medical sciences; Food engineering; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; Homoserine Dehydrogenase - metabolism; Life Sciences; Lysine - metabolism; Saccharopine Dehydrogenases - metabolism; Varietal selection. Specialized plant breeding, plant breeding aims; Yield, quality, earliness, varia; Zea mays - enzymology; Zea mays - genetics; Zea mays - growth & development; Monocotyledones; Storage protein; Biosynthesis; Genetic determinism; Cereal crop; Enzymatic activity; Gramineae; Quality; Angiospermae; Endosperm; Zein; Homoserine dehydrogenase; Biochemical analysis; Zea mays; Saccharopine dehydrogenase (NADP; Enzyme; Transferases; Nutritive value; Saccharopine dehydrogenase (NAD; Lysine; Aminoacid; Genetic improvement; L-lysine-forming; Spermatophyta; Oxidoreductases; Mutation; Aspartate kinase; L-glutamate-forming; ESSENTIAL AMINO ACIDS; Protein content
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf980940r

Quality protein maize (QPM) varieties have been produced by the introduction of opaque-2 modifier genes. Two QPM varieties, BR451 and BR473, a wild type and an opaque-2 variety, have been used to study key enzymes controlling lysine metabolism in the endosperm during development. Aspartate kinase and homoserine dehydrogenase enzymes, which are involved in lysine and threonine biosynthesis, respectively, exhibited identical activity patterns during endosperm development, with a maximum specific activity at 16 days after pollination. The QPM varieties exhibited higher levels of aspartate kinase activity in the endosperm, suggesting an increased rate of lysine biosynthesis when compared to the opaque-2 and wild-type genotypes. Similar results were observed for the lysine ketoglutarate reductase and saccharopine dehydrogenase enzymes, which form a single bifunctional polypetide involved in endosperm lysine degradation. Both enzyme activities were strongly reduced in the opaque-2 maize variety when compared to the wild-type maize, whereas the QPM varieties exhibited even lower levels of lysine ketoglutarate reductase−saccharopine dehydrogenase activities when compared to the opaque-2 variety. The developmental pattern of enzyme activity showed a different profile when compared to the enzymes involved in lysine biosynthesis, with activity being detected only 12−16 days after pollination (DAP) and maximum activities ∼24 DAP. These results also suggest that the modifier genes have intensified the effect of the opaque-2 mutation on lysine ketoglutarate reductase−saccharopine dehydrogenase. These alterations lead to an increase in soluble lysine in the endosperm of the QPM varieties when compared to the opaque-2 and wild type. Keywords: Quality protein maize; aspartate kinase; homoserine dehydrogenase; lysine ketoglutarate reductase−saccharopine dehydrogenase; opaque-2