Diaminopimelate Decarboxylase of Sporulating Bacteria

Abstract

The meso -diaminopimelate (DAP) decarboxylase of Bacillus licheniformis , a pyridoxal phosphate-requiring enzyme, was stabilized in vitro by 0.15 m sodium phosphate buffer ( p H 7.0) containing 1 m m 2,3-dimercaptopropan-1-ol, 100 μg of pyridoxal phosphate per ml, and 3 m m DAP. When the meso -DAP concentration was varied, the enzyme in cell-free extracts of B. licheniformis exhibited Michaelis-Menten kinetics. Pyridoxal phosphate was the only pyridoxine derivative which acted as a cofactor. The enzyme was subject to both inhibition and repression by l -lysine. The inhibitory effect of lysine was on the K m ( meso -DAP). A maximum repression of about 20% was obtained. No significant inhibition or activation was produced by cadaverine, dipicolinic acid, phenylalanine, pyruvate, ethylenediamine-tetraacetate, adenosine triphosphate, adenosine diphosphate, or adenosine monophosphate. When B. licheniformis was grown in an ammonium lactate-glucose-salts medium, an increase in DAP decarboxylase specific activity occurred during cellular growth with a maximal specific activity at the end of the exponential phase. As soon as growth ceased, the specific activity of the enzyme decreased to approximately one-half of the maximal specific activity and remained at this level thereafter. When B. cereus was grown in complex media, there was an increase in DAP decarboxylase specific activity up to the end of the exponential phase. Thereafter, the specific activity decreased to a nondetectable level in 4 hr. Dipicolinic acid synthesis was first detected 15 min later and was essentially complete after an additional 2.5 hr. The significance of the disappearance of DAP decarboxylase in B. cereus was discussed with regard to control of dipicolinic acid and spore mucopeptide biosynthesis.