Biochemical analyses of ppGpp effect on adenylosuccinate synthetases, key enzymes in purine biosynthesis in rice.

The ppGpp-signaling system functions in plant chloroplasts. In bacteria, a negative effect of ppGpp on adenylosuccinate synthetase (AdSS) has been suggested. Our biochemical analysis also revealed rice AdSS homologs are apparently sensitive to ppGpp. However, further investigation clarified that this phenomenon is cancelled by the high substrate affinity to the enzymes, leading to a limited effect of ppGpp on adenylosuccinate synthesis.