PubMed · 14631784
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Tomoyuki Yamaya. 2003. [Nitrogen remobilization].. https://pubmed.ncbi.nlm.nih.gov/14631784/
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The active site and substrate-binding mode of MD-ACO1 (Malus domestica Borkh. 1-aminocyclopropane-1-carboxylate oxidase) have been determined using site-directed mutagenesis and comparative modelling methods. The MD-ACO1 protein folds into a compact jelly-roll motif comprised of eight a-helices, 12 b-strands and several long loops. The active site is well defined as a wide cleft near the C-terminus. The co-substrate ascorbate is located in cofactor Fe2+-binding pocket, the so-called '2-His-1-carboxylate facial triad'. In addition, our results reveal that Arg244 and Ser246 are involved in generating the reaction product during enzyme catalysis. The structure agrees well with the biochemical and site-directed mutagenesis results. The three-dimensional structure together with the steady-state kinetics of both the wild-type and mutant MD-ACO1 proteins reveal how the substrate specificity of MD-ACO1 is involved in the catalytic mechanism, providing insights into understanding the fruit ripening process at atomic resolution.
In this paper are presented structural analysis and expression studies of one genomic clone encoding a 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) from papaya. Using RT-PCR amplification of ACC oxidase cDNAs from ripe papaya, a product of 800 bp was obtained, which after sequence analysis was found to code for a protein highly homologous to ACC oxidase proteins. This PCR product was used as a probe for screening a genomic library, and two different groups of clones were obtained as indicated by restriction mapping. One clone (CPACCO-1) was selected for further study and fully sequenced. Comparison of this sequence with the PCR product and other cloned ACC oxidase genes revealed that CPACCO-1 encoded the transcript in four exons interrupted by three introns. Southern blot analysis showed one or two major bands hybridized to the PCR probe, suggesting that the ACC oxidase gene is present in one or two copies in the papaya genome. By northern blot analysis it was found that the ACC oxidase transcripts appear in the pulp earlier than in the peel, suggesting a developmental regulation. A wounding experiment revealed the highest expression of this gene by 2 h. Transcriptional regulation by ethylene could be due to the presence of a putative GCC box in the promoter region.
The Gly decarboxylase complex (GDC) is abundant in mitochondria of C3 leaves and functions in photorespiratory carbon recovery. However, expression of GDC component proteins has generally been less evident in non-green tissues. Here we report an aspen (Populus tremuloides Michx.) PtgdcH1 gene, encoding a GDC subunit H-protein that is phylogenetically distinct from previously characterized photorespiratory H-proteins. Strong expression of PtgdcH1 in root tips and developing xylem suggests that GDC supports a very active C1 metabolism in non-photosynthetic tissues of aspen.