Crystal structure of the indole-3-acetic acid-catabolizing enzyme DAO1 from Arabidopsis thaliana.

Indole-3-acetic acid (IAA), the major form of the plant hormone auxin, regulates almost every aspect of plant growth and development. Therefore, auxin homeostasis is an essential process in plants. Different metabolic routes are involved in auxin homeostasis, but the catabolic pathway has remained elusive until recent studies identified DIOXYGENASE FOR AUXIN OXIDATION (DAO) from rice and Arabidopsis thaliana.

Structural and mutational analyses of the bifunctional arginine dihydrolase and ornithine cyclodeaminase AgrE from the cyanobacterium .

In cyanobacteria, metabolic pathways that use the nitrogen-rich amino acid arginine play a pivotal role in nitrogen storage and mobilization. The N-terminal domains of two recently identified bacterial enzymes: ArgZ from and AgrE from , have been found to contain an arginine dihydrolase. This enzyme provides catabolic activity that converts arginine to ornithine, resulting in concomitant release of CO and ammonia.

Crystal structure and mutational analyses of ribokinase from Arabidopsis thaliana.

Nitrogen remobilization is a key issue in plants. Recent studies in Arabidopsis thaliana have revealed that nucleoside catabolism supplies xanthine, a nitrogen-rich compound, to the purine ring catabolic pathway, which liberates ammonia from xanthine for reassimilation into amino acids. Similarly, pyrimidine nuclosides are degraded and the pyrimidine bases are fully catabolized.