02601naa a2200325 a 450000100080000000500110000800800410001910000190006024501120007926000090019152017510020065000120195165000110196365000110197465000110198565000100199665000140200665000140202065000130203465300120204765300130205965300120207265300080208465300120209270000180210470000240212270000170214670000190216377300930218214851832018-06-07       1999    bl uuuu     u00u1 u    #d1 aGAZIOLA, S. A.  aQuality protein maizeba biochemical study of enzymes involved in lysine metabolism.h[electronic resource]  c1999  aQuality 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 beeen 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 activity 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 ensyme 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.  aenzymes  alysine  aEnzima  aLisina  aMilho  aProteína  aQualidade  aZea Mays  aOpaco-2  aOpaque-2  aProtein  aQPM  aQuality1 aALESSI, E. S.1 aGUIMARAES, P. E. O.1 aDAMERVAL, C.1 aAZEVEDO, R. A.  tJournal of Agricultural and Food Chemistry, Washingtongv. 47, n. 3, p. 1268-1275, 1999.