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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 12
BKCSDE 21(12)
December 20, 2000 

Regulatory Mechanism of L-Alanine Dehydrogenase from Bacillus subtilis
Soo-Ja Kim, Yu Jin Kim, Mi Ran Seo, Bong Sook Jhun
L-alanine dehydrogenase from Bacillus subtilis exhibits allosteric kinetic properties in the presence of Zn2+ .Zn2+ induces the binding of substrate (L-alanine) to be cooperative at pH 8.0. The effect of pH variation between pH 7.0 and pH 10.0 on the inhibition by Zn2+ correlates with the pH effect on the Km values for L-alanine within these pH range indicating that Zn2+ and substrate compete for the same site. No such cooperativity is induced by Zn2+ when the reaction is carried out at pH 10. At this higher pH, Zn2+ binds with the enzyme with lower affinity and noncompetitive with respect to L-alanine. Inhibition of L-alanine dehydrogenase by Zn2+ depends on the ionic strength. Increase in KCl concentation reduced the inhibition, but allosteric property in Zn2+ binding is conserved. A model for the regulatory mechanism of L-alanine dehydrogenase as a noncooperative substrate-cooperative cofactor allosteric enzyme, which is compatible in both concerted and the sequential allosteric mechanism, is proposed.
1217 - 1221
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