Dihydrodipicolinate synthase in opaque and floury maize mutants

Dihydrodipicolinate synthase (DHDPS, EC 4.2.1.52) was isolated and studied in four high-lysine maize mutants (Oh43o1, Oh43o2, Oh43fl1 and Oh43fl2). The activity of DHDPS was analyzed at 16, 20, and 24 DAP and characterized in the presence of the amino acids, lysine, S-(2-aminoethyl)-l-cysteine (AEC), S-adenosylmethionine (SAM) and calcium. The results indicated that DHDPS was strongly inhibited by lysine, and that there was little variation between the mutants, indicating that lysine accumulation in these mutants may be more dependent on other enzymes involved in lysine metabolism. The higher concentrations of lysine observed in the seeds of the mutants at maturity may be explained by the accumulation of soluble lysine caused by a reduction in lysine degradation, or by changes in the distribution of high lysine containing storage proteins.