A new flavin enzyme catalyzing the reduction of dihydrodipicolinate in sporulating Bacillus subtilis. II. Kinetics and regulatory function.

Dihydrodipicolinate reductase in Bacillus subtilis PCI 219 had FMN as a prosthetic group, and the hydrogen transfer pathway is considered to be NADPH yields FMN yields dihydrodipicolinate. Linewaver-Burk plots of the reciprocal of the activity against the reciprocal of the concentration of either of the two substrates, dihydrodipocolinate and NADPH, are consistent with a reaction mechanism involving interconversion of two free forms of the enzyme by the two substrates. The Km values obtained from the secondary plots are 0.77 mM for dihydrodipicolinate and 72 muM for NADPH. Inhibition by dipicolinate is competitive with NADPH and noncompetitive with dihydrodipicolinate, and shows positive cooperativity. The possible metabolic role of the reductase in sporulating Bacillus subtilis is discussed in connection with regulation of the biosyntheses of dipicolinate and diaminopimelate.