Agriculture is dependent on biologically fixed nitrogen occurring between rhizobacteria and plants. Elevated levels of ethylene inhibit the association between plants and rhizobacteria preventing nitrogen fixation.  The enzyme 1-aminocyclopropane-1-carboxylate deaminase (ACCD) decreases the level of ethylene in plants by converting 1-aminocyclopropane-1-carboxylate (ACC), a precursor to ethylene, to a-ketobutyrate and ammonia. This study investigated ACCDs among 48 Sinorhizobium strains. Genomic analysis revealed proteins with a range of 33 to 100% identity to previously reported ACCDs. The ACCD homologs were analyzed using biochemical assays, sequence alignments and comparative 3D modeling of pyridoxal-5'-phosphate (PLP) active sites. Biochemical assays showed that only proteins with highly conserved amino acid sequences (>90%) catalyzed the conversion of ACC to a-ketobutyrate and ammonium. Sequence alignments and comparative 3D modeling of the PLP active sites suggest that enzymatic inactivity is due to the absence of a hydrogen bonding from a glycine residue to the nitrogen atom of PLP cofactor.

Biochemical characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminases from nitrogen-fixing bacteria

245th National Meeting (2013)

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