A small-molecule screen identifies L-kynurenine as a competitive inhibitor of TAA1/TAR activity in ethylene-directed auxin biosynthesis and root growth in Arabidopsis.
(9/15)
Disturbed local auxin homeostasis enhances cellular anisotropy and reveals alternative wiring of auxin-ethylene crosstalk in Brachypodium distachyon seminal roots.
(11/15)
Aromatic aminotransferase activity and indoleacetic acid production in Rhizobium meliloti.
(13/15)
Bacterial indoleacetic acid (IAA) production, which has been proposed to play a role in the Rhizobium-legume symbiosis, is a poorly understood process. Previous data have suggested that IAA biosynthesis in Rhizobium meliloti can occur through an indolepyruvate intermediate derived from tryptophan by an aminotransferase activity. To further examine this biosynthetic pathway, the aromatic aminotransferase (AAT) activity of Rhizobium meliloti 102F34 (F34) was characterized. At least four proteins were detected on nondenaturing gels of F34 protein extracts that exhibited AAT activity. All four of these AATs were constitutively produced and utilized the aromatic amino acids tryptophan, phenylalanine, and tyrosine as amino substrates. Two AATs were also capable of using aspartate. Plasmids from an F34 gene bank were identified that coded for the synthesis of at least three of these proteins, and the respective gene sequences were localized by transposon mutagenesis. Selected transposon insertions were recombined into the F34 genome to produce strains defective in two of these proteins (AAT1 and AAT2). Characterization of the mutants revealed that neither was essential for the biosynthesis of IAA in the absence of exogenous tryptophan, but that both contributed to IAA biosynthesis when high levels of exogenous tryptophan were present. AAT1 and AAT2 were also not required for the production of a minimal level of aromatic amino acids, but both were able to scavenge nitrogen from the aromatic amino acids during nitrogen deprivation. Neither AAT1 nor AAT2 was essential for symbiosis with alfalfa. (+info)
Tryptophan aminotransferase activity in rat liver.
(14/15)
By using an antiserum raised against rat liver tyrosine aminotransferase, it was shown that about 60% of tryptophan aminotransferase activity in rat liver extracts is catalysed by this enzyme. Induction of tryptophan aminotransferase activity by intraperitoneal injections of tryptophan or triamcinolone can be entirely attributed to the effects of these agents on tyrosine aminotransferase. The origin of the other 40% of tryptophan aminotransferase activity remains to be established. This activity increases after starvation for 48 h. It is unlikely that tryptophan transamination plays a quantitatively important role in the metabolism of tryptophan by the liver. (+info)
Peroxisomal localization and properties of tryptophan aminotransferase in plant leaves.
(15/15)
In spinach leaves, both tryptophan:glyoxylate aminotransferase and tryptophan:hydroxypyruvate aminotransferase activities were located only in the peroxisomes and in the soluble fraction. The two enzymes co-purified to homogeneity from both peroxisomal and soluble fractions of spinach leaves. The evidence indicates that the two activities are associated with the same protein. The peroxisomal and soluble enzyme preparations had nearly identical properties, suggesting that the soluble enzyme is from broken peroxisomes. The two enzyme preparations utilized various L-amino acids as amino donors in the following order of activity with glyoxylate as amino acceptor; serine greater than alanine greater than tryptophan greater than asparagine greater than 5-hydroxytryptophan. Other amino acids tested were all much less active. With L-tryptophan as amino donor, the effective amino acceptors were glyoxylate and hydroxypyruvate; other 2-oxo acids tested were all inactive. They had molecular weights of approximately 185,000 with four identical subunits, isoelectric points of 5.9, and pH optima between 8.0 and 8.5. (+info)